Network Working Group D. Farinacci Internet-Draft V. Fuller Intended status: Experimental D. Oran Expires: April 13, 2009 D. Meyer S. Brim cisco Systems October 10, 2008 Locator/ID Separation Protocol (LISP) draft-farinacci-lisp-09.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 13, 2009. Copyright Notice Copyright (C) The IETF Trust (2008). Farinacci, et al. Expires April 13, 2009 [Page 1] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 Abstract This draft describes a simple, incremental, network-based protocol to implement separation of Internet addresses into Endpoint Identifiers (EIDs) and Routing Locators (RLOCs). This mechanism requires no changes to host stacks and no major changes to existing database infrastructures. The proposed protocol can be implemented in a relatively small number of routers. This proposal was stimulated by the problem statement effort at the Amsterdam IAB Routing and Addressing Workshop (RAWS), which took place in October 2006. Farinacci, et al. Expires April 13, 2009 [Page 2] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 Table of Contents 1. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 8 4. Basic Overview . . . . . . . . . . . . . . . . . . . . . . . . 12 4.1. Packet Flow Sequence . . . . . . . . . . . . . . . . . . . 13 5. Tunneling Details . . . . . . . . . . . . . . . . . . . . . . 16 5.1. LISP IPv4-in-IPv4 Header Format . . . . . . . . . . . . . 17 5.2. LISP IPv6-in-IPv6 Header Format . . . . . . . . . . . . . 18 5.3. Tunnel Header Field Descriptions . . . . . . . . . . . . . 19 5.4. Dealing with Large Encapsulated Packets . . . . . . . . . 20 6. EID-to-RLOC Mapping . . . . . . . . . . . . . . . . . . . . . 22 6.1. Control Plane Packet Format . . . . . . . . . . . . . . . 22 6.1.1. LISP Packet Type Allocations . . . . . . . . . . . . . 24 6.1.2. Map-Request Message Format . . . . . . . . . . . . . . 24 6.1.3. EID-to-RLOC UDP Map-Request Message . . . . . . . . . 26 6.1.4. Map-Reply Message Format . . . . . . . . . . . . . . . 26 6.1.5. EID-to-RLOC UDP Map-Reply Message . . . . . . . . . . 29 6.2. Routing Locator Selection . . . . . . . . . . . . . . . . 29 6.3. Routing Locator Reachability . . . . . . . . . . . . . . . 30 6.4. Routing Locator Hashing . . . . . . . . . . . . . . . . . 32 6.5. Changing the Contents of EID-to-RLOC Mappings . . . . . . 33 6.5.1. Clock Sweep . . . . . . . . . . . . . . . . . . . . . 34 6.5.2. Solicit-Map-Request (SMR) . . . . . . . . . . . . . . 34 7. Router Performance Considerations . . . . . . . . . . . . . . 36 8. Deployment Scenarios . . . . . . . . . . . . . . . . . . . . . 37 8.1. First-hop/Last-hop Tunnel Routers . . . . . . . . . . . . 38 8.2. Border/Edge Tunnel Routers . . . . . . . . . . . . . . . . 38 8.3. ISP Provider-Edge (PE) Tunnel Routers . . . . . . . . . . 39 9. Mobility Considerations . . . . . . . . . . . . . . . . . . . 40 9.1. Site Mobility . . . . . . . . . . . . . . . . . . . . . . 40 9.2. Slow Endpoint Mobility . . . . . . . . . . . . . . . . . . 40 9.3. Fast Endpoint Mobility . . . . . . . . . . . . . . . . . . 40 9.4. Fast Network Mobility . . . . . . . . . . . . . . . . . . 42 10. Multicast Considerations . . . . . . . . . . . . . . . . . . . 43 11. Security Considerations . . . . . . . . . . . . . . . . . . . 44 12. Prototype Plans and Status . . . . . . . . . . . . . . . . . . 45 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 47 13.1. Normative References . . . . . . . . . . . . . . . . . . . 47 13.2. Informative References . . . . . . . . . . . . . . . . . . 47 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 50 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 51 Intellectual Property and Copyright Statements . . . . . . . . . . 52 Farinacci, et al. Expires April 13, 2009 [Page 3] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 1. Requirements Notation The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Farinacci, et al. Expires April 13, 2009 [Page 4] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 2. Introduction Many years of discussion about the current IP routing and addressing architecture have noted that its use of a single numbering space (the "IP address") for both host transport session identification and network routing creates scaling issues (see [CHIAPPA] and [RFC1498]). A number of scaling benefits would be realized by separating the current IP address into separate spaces for Endpoint Identifiers (EIDs) and Routing Locators (RLOCs); among them are: 1. Reduction of routing table size in the "default-free zone" (DFZ). Use of a separate numbering space for RLOCs will allow them to be assigned topologically (in today's Internet, RLOCs would be assigned by providers at client network attachment points), greatly improving aggregation and reducing the number of globally-visible, routable prefixes. 2. Easing of renumbering burden when clients change providers. Because host EIDs are numbered from a separate, non-provider- assigned and non-topologically-bound space, they do not need to be renumbered when a client site changes its attachment points to the network. 3. Traffic engineering capabilities that can be performed by network elements and do not depend on injecting additional state into the routing system. This will fall out of the mechanism that is used to implement the EID/RLOC split (see Section 4). 4. Mobility without address changing. Existing mobility mechanisms will be able to work in a locator/ID separation scenario. It will be possible for a host (or a collection of hosts) to move to a different point in the network topology either retaining its home-based address or acquiring a new address based on the new network location. A new network location could be a physically different point in the network topology or the same physical point of the topology with a different provider. This draft describes protocol mechanisms to achieve the desired functional separation. For flexibility, the document decouples the mechanism used for forwarding packets from that used to determine EID to RLOC mappings. This work is in response to and intended to address the problem statement that came out of the RAWS effort [RFC4984]. The Routing and Addressing problem statement can be found in [RADIR]. This draft focuses on a router-based solution. Building the solution into the network should facilitate incremental deployment of the Farinacci, et al. Expires April 13, 2009 [Page 5] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 technology on the Internet. Note that while the detailed protocol specification and examples in this document assume IP version 4 (IPv4), there is nothing in the design that precludes use of the same techniques and mechanisms for IPv6. It should be possible for IPv4 packets to use IPv6 RLOCs and for IPv6 EIDs to be mapped to IPv4 RLOCs. Related work on host-based solutions is described in Shim6 [SHIM6] and HIP [RFC4423]. Related work on a router-based solution is described in [GSE]. This draft attempts to not compete or overlap with such solutions and the proposed protocol changes are expected to complement a host-based mechanism when Traffic Engineering functionality is desired. Some of the design goals of this proposal include: 1. Minimize required changes to Internet infrastructure. 2. Require no hardware or software changes to end-systems (hosts). 3. Be incrementally deployable. 4. Require no router hardware changes. 5. Minimize router software changes. 6. Avoid or minimize packet loss when EID-to-RLOC mappings need to be performed. There are 4 variants of LISP, which differ along a spectrum of strong to weak dependence on the topological nature and possible need for routability of EIDs. The variants are: LISP 1: uses EIDs that are routable through the RLOC topology for bootstrapping EID-to-RLOC mappings. [LISP1] This was intended as a prototyping mechanism for early protocol implementation. It is now deprecated and should not be deployed. LISP 1.5: uses EIDs that are routable for bootstrapping EID-to-RLOC mappings; such routing is via a separate topology. LISP 2: uses EIDS that are not routable and EID-to-RLOC mappings are implemented within the DNS. [LISP2] LISP 3: uses non-routable EIDs that are used as lookup keys for a new EID-to-RLOC mapping database. Use of Distributed Hash Tables [DHTs] [LISPDHT] to implement such a database would be an area to explore. Other examples of new mapping database services are Farinacci, et al. Expires April 13, 2009 [Page 6] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 [CONS], [ALT], [RPMD], [NERD], and [APT]. This document will focus on LISP 1 and LISP 1.5, both of which rely on a router-based distributed cache and database for EID-to-RLOC mappings. The LISP 2 and LISP 3 mechanisms, which require separate EID-to-RLOC infrastructure, will be documented elsewhere. Farinacci, et al. Expires April 13, 2009 [Page 7] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 3. Definition of Terms Provider Independent (PI) Addresses: an address block assigned from a pool that is not associated with any service provider and is therefore not topologically-aggregatable in the routing system. Provider Assigned (PA) Addresses: a block of IP addresses that are assigned to a site by each service provider to which a site connects. Typically, each block is sub-block of a service provider CIDR block and is aggregated into the larger block before being advertised into the global Internet. Traditionally, IP multihoming has been implemented by each multi-homed site acquiring its own, globally-visible prefix. LISP uses only topologically-assigned and aggregatable address blocks for RLOCs, eliminating this demonstrably non-scalable practice. Routing Locator (RLOC): the IPv4 or IPv6 address of an egress tunnel router (ETR). It is the output of a EID-to-RLOC mapping lookup. An EID maps to one or more RLOCs. Typically, RLOCs are numbered from topologically-aggregatable blocks that are assigned to a site at each point to which it attaches to the global Internet; where the topology is defined by the connectivity of provider networks, RLOCs can be thought of as PA addresses. Multiple RLOCs can be assigned to the same ETR device or to multiple ETR devices at a site. Endpoint ID (EID): a 32-bit (for IPv4) or 128-bit (for IPv6) value used in the source and destination address fields of the first (most inner) LISP header of a packet. The host obtains a destination EID the same way it obtains an destination address today, for example through a DNS lookup or SIP exchange. The source EID is obtained via existing mechanisms used to set a host's "local" IP address. An EID is allocated to a host from an EID-prefix block associated with the site where the host is located. An EID can be used by a host to refer to other hosts. EIDs MUST NOT be used as LISP RLOCs. Note that EID blocks may be assigned in a hierarchical manner, independent of the network topology, to facilitate scaling of the mapping database. In addition, an EID block assigned to a site may have site-local structure (subnetting) for routing within the site; this structure is not visible to the global routing system. EID-prefix: A power-of-2 block of EIDs which are allocated to a site by an address allocation authority. EID-prefixes are associated with a set of RLOC addresses which make up a "database mapping". EID-prefix allocations can be broken up into smaller blocks when an RLOC set is to be associated with the smaller EID- prefix. A globally routed address block (whether PI or PA) is not Farinacci, et al. Expires April 13, 2009 [Page 8] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 an EID-prefix. However, a globally routed address block may be removed from global routing and reused as an EID-prefix. A site that receives an explicitly allocated EID-prefix may not use that EID-prefix as a globally routed prefix assigned to RLOCs. End-system: is an IPv4 or IPv6 device that originates packets with a single IPv4 or IPv6 header. The end-system supplies an EID value for the destination address field of the IP header when communicating globally (i.e. outside of it's routing domain). An end-system can be a host computer, a switch or router device, or any network appliance. Ingress Tunnel Router (ITR): a router which accepts an IP packet with a single IP header (more precisely, an IP packet that does not contain a LISP header). The router treats this "inner" IP destination address as an EID and performs an EID-to-RLOC mapping lookup. The router then prepends an "outer" IP header with one of its globally-routable RLOCs in the source address field and the result of the mapping lookup in the destination address field. Note that this destination RLOC may be an intermediate, proxy device that has better knowledge of the EID-to-RLOC mapping closer to the destination EID. In general, an ITR receives IP packets from site end-systems on one side and sends LISP-encapsulated IP packets toward the Internet on the other side. Specifically, when a service provider prepends a LISP header for Traffic Engineering purposes, the router that does this is also regarded as an ITR. The outer RLOC the ISP ITR uses can be based on the outer destination address (the originating ITR's supplied RLOC) or the inner destination address (the originating hosts supplied EID). TE-ITR: is an ITR that is deployed in a service provider network that prepends an additional LISP header for Traffic Engineering purposes. Egress Tunnel Router (ETR): a router that accepts an IP packet where the destination address in the "outer" IP header is one of its own RLOCs. The router strips the "outer" header and forwards the packet based on the next IP header found. In general, an ETR receives LISP-encapsulated IP packets from the Internet on one side and sends decapsulated IP packets to site end-systems on the other side. ETR functionality does not have to be limited to a router device. A server host can be the endpoint of a LISP tunnel as well. Farinacci, et al. Expires April 13, 2009 [Page 9] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 TE-ETR: is an ETR that is deployed in a service provider network that strips an outer LISP header for Traffic Engineering purposes. xTR: is a reference to an ITR or ETR when direction of data flow is not part of the context description. xTR refers to the router that is the tunnel endpoint. Used synonymously with the term "Tunnel Router". For example, "An xTR can be located at the Customer Edge (CE) router", meaning both ITR and ETR functionality is at the CE router. EID-to-RLOC Cache: a short-lived, on-demand database in an ITR that stores, tracks, and is responsible for timing-out and otherwise validating EID-to-RLOC mappings. This cache is distinct from the "database", the cache is dynamic, local, and relatively small while the database is distributed, relatively static, and much more global in scope. EID-to-RLOC Database: a global distributed database that contains all known EID-prefix to RLOC mappings. Each potential ETR typically contains a small piece of the database: the EID-to-RLOC mappings for the EID prefixes "behind" the router. These map to one of the router's own, globally-visible, IP addresses. Recursive Tunneling: when a packet has more than one LISP IP header. Additional layers of tunneling may be employed to implement traffic engineering or other re-routing as needed. When this is done, an additional "outer" LISP header is added and the original RLOCs are preserved in the "inner" header. Any references to tunnels in this specification refers to dynamic encapsulating tunnels and never are they staticly configured. Reencapsulating Tunnels: when a packet has no more than one LISP IP header (two IP headers total) and when it needs to be diverted to new RLOC, an ETR can decapsulate the packet (remove the LISP header) and prepend a new tunnel header, with new RLOC, on to the packet. Doing this allows a packet to be re-routed by the re- encapsulating router without adding the overhead of additional tunnel headers. Any references to tunnels in this specification refers to dynamic encapsulating tunnels and never are they staticly configured. LISP Header: a term used in this document to refer to the outer IPv4 or IPv6 header, a UDP header, and a LISP header, an ITR prepends or an ETR strips. Farinacci, et al. Expires April 13, 2009 [Page 10] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 Address Family Indicator (AFI): a term used to describe an address encoding in a packet. An address family currently pertains to an IPv4 or IPv6 address. See [AFI] for details. Negative Mapping Entry: also known as a negative cache entry, is an EID-to-RLOC entry where an EID-prefix is advertised or stored with no RLOCs. That is, the locator-set for the EID-to-RLOC entry is empty or has an encoded locator count of 0. This type of entry could be used to describe a prefix from a non-LISP site, which is explicitly not in the mapping database. Data Probe: a LISP-encapsulated data packet where the inner header destination address equals the outer header destination address used to trigger a Map-Reply by a decapsulating ETR. In addition, the original packet is decapsulated and delivered to the destination host. A Data Probe is used in some of the mapping database designs to "probe" or request a Map-Reply from an ETR; in other cases, Map-Requests are used. See each mapping database design for details. Farinacci, et al. Expires April 13, 2009 [Page 11] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 4. Basic Overview One key concept of LISP is that end-systems (hosts) operate the same way they do today. The IP addresses that hosts use for tracking sockets, connections, and for sending and receiving packets do not change. In LISP terminology, these IP addresses are called Endpoint Identifiers (EIDs). Routers continue to forward packets based on IP destination addresses. These addresses are referred to as Routing Locators (RLOCs). Most routers along a path between two hosts will not change; they continue to perform routing/forwarding lookups on addresses (RLOCs) in the IP header. This design introduces "Tunnel Routers", which prepend LISP headers on host-originated packets and strip them prior to final delivery to their destination. The IP addresses in this "outer header" are RLOCs. During end-to-end packet exchange between two Internet hosts, an ITR prepends a new LISP header to each packet and an egress tunnel router strips the new header. The ITR performs EID-to-RLOC lookups to determine the routing path to the the ETR, which has the RLOC as one of its IP addresses. Some basic rules governing LISP are: o End-systems (hosts) only send to addresses which are EIDs. They don't know addresses are EIDs versus RLOCs but assume packets get to LISP routers, which in turn, deliver packets to the destination the end-system has specified. o EIDs are always IP addresses assigned to hosts. o LISP routers mostly deal with Routing Locator addresses. See details later in Section 4.1 to clarify what is meant by "mostly". o RLOCs are always IP addresses assigned to routers; preferably, topologically-oriented addresses from provider CIDR blocks. o When a router originates packets it may use as a source address either an EID or RLOC. When acting as a host (e.g. when terminating a transport session such as SSH, TELNET, or SNMP), it may use an EID that is explicitly assigned for that purpose. An EID that identifies the router as a host MUST NOT be used as an RLOC. Keep in mind that an EID is only routable within the scope of a site. A typical BGP configuration might demonstrate this "hybrid" EID/RLOC usage where a router could use its "host-like" EID to terminate iBGP sessions to other routers in a site while at the same time using RLOCs to terminate eBGP sessions to routers Farinacci, et al. Expires April 13, 2009 [Page 12] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 outside the site. o EIDs are not expected to be usable for global end-to-end communication in the absence of an EID-to-RLOC mapping operation. They are expected to be used locally for intra-site communication. o EID prefixes are likely to be hierarchically assigned in a manner which is optimized for administrative convenience and to facilitate scaling of the EID-to-RLOC mapping database. The hierarchy is based on a address allocation hierarchy which is not dependent on the network topology. o EIDs may also be structured (subnetted) in a manner suitable for local routing within an autonomous system. An additional LISP header may be pre-pended to packets by a transit router (i.e. TE-ITR) when re-routing of the end-to-end path for a packet is desired. An obvious instance of this would be an ISP router that needs to perform traffic engineering for packets in flow through its network. In such a situation, termed Recursive Tunneling, an ISP transit acts as an additional ingress tunnel router and the RLOC it uses for the new prepended header would be either an TE-ETR within the ISP (along intra-ISP traffic engineered path) or in an TE-ETR within another ISP (an inter-ISP traffic engineered path, where an agreement to build such a path exists). This specification mandates that no more than two LISP headers get prepended to a packet. This avoids excessive packet overhead as well as possible encapsulation loops. It is believed two headers is sufficient, where the first prepended header is used at a site for Locator/ID separation and second prepended header is used inside a service provider for Traffic Engineering purposes. Tunnel Routers can be placed fairly flexibly in a multi-AS topology. For example, the ITR for a particular end-to-end packet exchange might be the first-hop or default router within a site for the source host. Similarly, the egress tunnel router might be the last-hop router directly-connected to the destination host. Another example, perhaps for a VPN service out-sourced to an ISP by a site, the ITR could be the site's border router at the service provider attachment point. Mixing and matching of site-operated, ISP-operated, and other tunnel routers is allowed for maximum flexibility. See Section 8 for more details. 4.1. Packet Flow Sequence This section provides an example of the unicast packet flow with the following parameters: Farinacci, et al. Expires April 13, 2009 [Page 13] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 o Source host "host1.abc.com" is sending a packet to "host2.xyz.com", exactly what host1 would do if the site was not using LISP. o Each site is multi-homed, so each tunnel router has an address (RLOC) assigned from each of the site's attached service provider address blocks. o The ITR and ETR are directly connected to the source and destination, respectively. Client host1.abc.com wants to communicate with server host2.xyz.com: 1. host1.abc.com wants to open a TCP connection to host2.xyz.com. It does a DNS lookup on host2.xyz.com. An A/AAAA record is returned. This address is used as the destination EID and the locally-assigned address of host1.abc.com is used as the source EID. An IP/IPv6 packet is built using the EIDs in the IP/IPv6 header and sent to the default router. 2. The default router is configured as an ITR. The ITR must be able to map the EID destination to an RLOC of the ETR at the destination site. The ITR prepends a LISP header to the packet, with one of its RLOCs as the source IP/IPv6 address. The destination EID from the original packet header is used as the destination IP/IPv6 in the prepended LISP header. Subsequent packets will be sent using the same LISP header until EID-to-RLOC mapping is learned. 3. In LISP 1, the packet is routed through the Internet as it is today. In LISP 1.5, the packet is routed on a different topology which may have EID prefixes distributed and advertised in an aggregatable fashion. In either case, the packet arrives at the ETR. The router is configured to "punt" the packet to the router's processor. See Section 7 for more details. 4. The LISP header is stripped so that the packet can be forwarded by the router control plane. The router looks up the destination EID in the router's EID-to-RLOC database (not the cache, but the configured data structure of RLOCs). An EID-to-RLOC Map-Reply message is originated by the egress router and is addressed to the source RLOC from the LISP header of the original packet (this is the ITR). The source RLOC in the IP header of the UDP message is one of the ETR's RLOCs (one of the RLOCs that is embedded in the UDP payload). 5. The ITR receives the UDP Map-Reply message, parses the message (to check for format validity) and stores the EID-to-RLOC Farinacci, et al. Expires April 13, 2009 [Page 14] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 information from the packet. This information is put in the ITR's EID-to-RLOC mapping cache (this is the on-demand cache, the cache where entries time out due to inactivity). 6. Subsequent packets from host1.abc.com to host2.xyz.com will have a LISP header prepended by the ITR using the appropriate RLOC as the LISP header destination address learned from the ETR. Note, the packet may be sent to a different ETR than the one which returned the UDP Map-Reply. 7. The ETR receives these packets directly (since the destination address is one of its assigned IP addresses), strips the LISP header and forwards the packets to the attached destination host. In order to eliminate the need for a mapping lookup in the reverse direction, an ETR MAY create a cache entry that maps the source EID (inner header source IP address) to the source RLOC (outer header source IP address) in a received LISP packet. Such a cache entry is termed a "gleaned" mapping and only contains a single RLOC for the EID in question. More complete information about additional RLOCs SHOULD be verified by sending a LISP Map-Request for that EID. Both ITR and the ETR may also influence the decision the other makes in selecting an RLOC. See Section 6 for more details. Farinacci, et al. Expires April 13, 2009 [Page 15] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 5. Tunneling Details This section describes the LISP Data Message which defines the tunneling header used to encapsulate IPv4 and IPv6 packets which contain EID addresses. Even though the following formats illustrate IPv4-in-IPv4 and IPv6-in-IPv6 encapsulations, the other 2 combinations are supported as well. Since additional tunnel headers are prepended, the packet becomes larger and in theory can exceed the MTU of any link traversed from the ITR to the ETR. It is recommended, in IPv4 that packets do not get fragmented as they are encapsulated by the ITR. Instead, the packet is dropped and an ICMP Too Big message is returned to the source. Based on informal surveys of large ISP traffic patterns, it appears that most transit paths can accommodate a path MTU of at least 4470 bytes. The exceptions, in terms of data rate, number of hosts affected, or any other metric are expected to be vanishingly small. To address MTU concerns, mainly raised on the RRG mailing list, the LISP deployment process will include collecting data during its pilot phase to either verify or refute the assumption about minimum available MTU. If the assumption proves true and transit networks with links limited to 1500 byte MTUs are corner cases, it would seem more cost-effective to either upgrade or modify the equipment in those transit networks to support larger MTUs or to use existing mechanisms for accommodating packets that are too large. For this reason, there is currently no plan for LISP to add an additional, complex mechanism for implementing fragmentation and reassembly in the face of limited-MTU transit links. If analysis during LISP pilot deployment reveals that the assumption of essentially ubiquitous, 4470+ byte transit path MTUs, is incorrect, then LISP can be modified prior to protocol standardization to add support for one of the proposed fragmentation and reassembly schemes. Note that one simple scheme is detailed in Section 5.4. Farinacci, et al. Expires April 13, 2009 [Page 16] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 5.1. LISP IPv4-in-IPv4 Header Format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / |Version| IHL |Type of Service| Total Length | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / | Identification |Flags| Fragment Offset | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ OH | Time to Live | Protocol = 17 | Header Checksum | \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ | Source Routing Locator | \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ | Destination Routing Locator | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / | Source Port = xxxx | Dest Port = 4341 | UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ | UDP Length | UDP Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / |S|M| Locator Reach Bits | LISP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ | Nonce | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / |Version| IHL |Type of Service| Total Length | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / | Identification |Flags| Fragment Offset | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IH | Time to Live | Protocol | Header Checksum | \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ | Source EID | \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ | Destination EID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Farinacci, et al. Expires April 13, 2009 [Page 17] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 5.2. LISP IPv6-in-IPv6 Header Format +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / |Version| Traffic Class | Flow Label | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / | Payload Length | Next Header=17| Hop Limit | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | O + + u | | t + Source Routing Locator + e | | r + + | | H +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ d | | r + + | | \ + Destination Routing Locator + \ | | \ + + \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / | Source Port = xxxx | Dest Port = 4341 | UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ | UDP Length | UDP Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / |S|M| Locator Reach Bits | LISP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ | Nonce | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / |Version| Traffic Class | Flow Label | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / | Payload Length | Next Header | Hop Limit | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | I + + n | | n + Source EID + e | | r + + | | H +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ d | | r + + | | Farinacci, et al. Expires April 13, 2009 [Page 18] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 \ + Destination EID + \ | | \ + + \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 5.3. Tunnel Header Field Descriptions IH Header: is the inner header, preserved from the datagram received from the originating host. The source and destination IP addresses are EIDs. OH Header: is the outer header prepended by an ITR. The address fields contain RLOCs obtained from the ingress router's EID-to- RLOC cache. The IP protocol number is "UDP (17)" from [RFC0768]. UDP Header: contains a random source port allocated by the ITR when encapsulating a packet. Alternatively, see Section 6.4 for a suggested hash algorithm to select a source port based on the 5-tuple of the inner header. The destination port MUST be set to the well-known IANA assigned port value 4341. UDP Checksum: this field field MUST be transmitted as 0 and ignored on receipt by the ETR. Note, even when the UDP checksum is transmitted as 0 an intervening NAT device can recalculate the checksum and rewrite the UDP checksum field to non-zero. For performance reasons, the ETR MUST ignore the checksum and MUST not do a checksum computation. UDP Length: for an IPv4 encapsulated packet, the inner header Total Length plus the UDP and LISP header lengths are used. For an IPv6 encapsulated packet, the inner header Payload Length plus the size of the IPv6 header (40 bytes) plus the size of the UDP and LISP headers are used. The UDP header length is 8 bytes. The LISP header length is 8 bytes when no loc-reach-bit header extensions are used. S: this is the SMR bit. See Section 6.5.2 for details. LISP Locator Reach Bits: in the LISP header are set by an ITR to indicate to an ETR the reachability of the Locators in the source site. Each RLOC in a Map-Reply is assigned an ordinal value from 0 to n-1 (when there are n RLOCs in a mapping entry). The Locator Reach Bits are numbered from 0 to n-1 from the right significant bit of the 30-bit field. When a bit is set to 1, the ITR is indicating to the ETR the RLOC associated with the bit ordinal is reachable. See Section 6.3 for details on how an ITR can Farinacci, et al. Expires April 13, 2009 [Page 19] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 determine other ITRs at the site are reachable. When a site has multiple EID-prefixes which result in multiple mappings (where each could have a different locator-set), the Locator Reach Bits setting in an encapsulated packet MUST reflect the mapping for the EID-prefix that the inner-header source EID address matches. When the M bit is set, an additional 32-bit locator reachability field follows, which contains an M-bit field and 31 locator reachability bits. The M-bit may be set for further extension (and so on). This extension mechanism allows an EID to be mapped to an arbitrary number of RLOCs, subject only to the maximum number of 32-bit fields that can fit into the response packet. For practical purposes, a future version of this specification will likely set a limit on the number of these fields. LISP Nonce: is a 32-bit value that is randomly generated by an ITR. It is used to test route-returnability when xTRs exchange encapsulated data packets with the SMR bit set, Data-Probe, Map- Request, or Map-Reply messages. When doing Recursive Tunneling: o The OH header Time to Live field (or Hop Limit field, in case of IPv6) MUST be copied from the IH header Time to Live field. o The OH header Type of Service field (or the Traffic Class field, in the case of IPv6) SHOULD be copied from the IH header Type of Service field. When doing Re-encapsulated Tunneling: o The new OH header Time to Live field SHOULD be copied from the stripped OH header Time to Live field. o The new OH header Type of Service field SHOULD be copied from the stripped OH header Type of Service field. Copying the TTL serves two purposes: first, it preserves the distance the host intended the packet to travel; second, and more importantly, it provides for suppression of looping packets in the event there is a loop of concatenated tunnels due to misconfiguration. 5.4. Dealing with Large Encapsulated Packets In the event that the MTU issues mentioned above prove to be more serious than expected, this section proposes a simple and stateless mechanism to deal with large packets. The mechanism is described as follows: Farinacci, et al. Expires April 13, 2009 [Page 20] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 1. Define an architectural constant S for the maximum size of a packet, in bytes, an ITR would receive from a source inside of its site. 2. Define L to be the maximum size, in bytes, a packet of size S would be after the ITR prepends the LISP header, UDP header, and outer network layer header of size H. 3. Calculate: S + H = L. When an ITR receives a packet from a site-facing interface and adds H bytes worth of encapsulation to yield a packet size of L bytes, it resolves the MTU issue by first splitting the original packet into 2 equal-sized fragments. A LISP header is then pre-pended to each fragment. This will ensure that the new, encapsulated packets are of size (S/2 + H), which is always below the effective tunnel MTU. When an ETR receives encapsulated fragments, it treats them as two individually encapsulated packets. It strips the LISP headers then forwards each fragment to the destination host of the destination site. The two fragments are reassembled at the destination host into the single IP datagram that was originated by the source host. This behavior is performed by the ITR when the source host originates a packet with the DF field of the IP header is set to 0. When the DF field of the IP header is set to 1, or the packet is an IPv6 packet originated by the source host, the ITR will drop the packet when the size is greater than L, and sends an ICMP Too Big message to the source with a value of S, where S is (L - H). This specification recommends that L be defined as 1500. Farinacci, et al. Expires April 13, 2009 [Page 21] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 6. EID-to-RLOC Mapping 6.1. Control Plane Packet Format When LISP 1 or LISP 1.5 is used, new UDP packet types encode the EID- to-RLOC mappings: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version| IHL |Type of Service| Total Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Identification |Flags| Fragment Offset | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Time to Live | Protocol = 17 | Header Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Routing Locator | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Destination Routing Locator | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / | Source Port | Dest Port | UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ | UDP Length | UDP Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | LISP Message | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version| Traffic Class | Flow Label | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Payload Length | Next Header=17| Hop Limit | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Source Routing Locator + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Destination Routing Locator + Farinacci, et al. Expires April 13, 2009 [Page 22] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / | Source Port | Dest Port | UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ | UDP Length | UDP Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | LISP Message | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The LISP UDP-based messages are the Map-Request and Map-Reply messages. When a UDP Map-Request is sent, the UDP source port is chosen by the sender and the destination UDP port number is set to 4342. When a UDP Map-Reply is sent, the source UDP port number is set to 4342 and the destination UDP port number is copied from the source port of either the Map-Request or the invoking data packet. The UDP Length field will reflect the length of the UDP header and the LISP Message payload. The UDP Checksum is computed and set to non-zero for Map-Request and Map-Reply messages. It MUST be checked on receipt and if the checksum fails, the packet MUST be dropped. LISP-CONS [CONS] use TCP to send LISP control messages. The format of control messages includes the UDP header so the checksum and length fields can be used to protect and delimit message boundaries. This main LISP specification is the authoritative source for message format definitions for the Map-Request and Map-Reply messages. Farinacci, et al. Expires April 13, 2009 [Page 23] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 6.1.1. LISP Packet Type Allocations This section will be the authoritative source for allocating LISP Type values. Current allocations are: Reserved: 0 b'0000' LISP Map-Request: 1 b'0001' LISP Map-Reply: 2 b'0010' LISP-CONS Open Message: 8 b'1000' LISP-CONS Push-Add Message: 9 b'1001' LISP-CONS Push-Delete Message: 10 b'1010' LISP-CONS Uneachable Message: 11 b'1011' 6.1.2. Map-Request Message Format +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |S|M| Locator Reach Bits | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Nonce | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Type=1 |A|R| Reserved | Record Count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source-EID-AFI | ITR-AFI | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source EID Address ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Originating ITR RLOC Address ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / | Reserved | EID mask-len | EID-prefix-AFI | Rec < +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ | EID-prefix ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Map-Reply Record ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Mapping Protocol Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Packet field descriptions: Farinacci, et al. Expires April 13, 2009 [Page 24] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 S: This is the SMR bit. See Section 6.5.2 for details. Locator Reach Bits: Refer to Section 5.3. Nonce: A 4-byte random value created by the sender of the Map- Request. Type: 1 (Map-Request) A: This is an authoritative bit, which is set to 0 for UDP-based Map- Requests sent by an ITR. See other control-specific documents [CONS] for TCP-based Map-Requests. R: When set, it indicates a Map-Reply Record segment is included in the Map-Request. Reserved: Set to 0 on transmission and ignored on receipt. Record Count: The number of records in this request message. A record is comprised of the portion of the packet is labeled 'Rec" above and occurs the number of times equal to Record count. Source-EID-AFI: Address family of the "Source EID Address" field. ITR-AFI: Address family of the "Originating ITR RLOC Address" field. Source EID Address: This is the EID of the source host which originated the packet which is invoking this Map-Request. Originating ITR RLOC Address: Used to give the ETR the option to return a Map-Reply in the address-family of this locator. EID mask-len: Mask length for EID prefix. EID-AFI: Address family of EID-prefix according to [RFC2434] EID-prefix: 4 bytes if an IPv4 address-family, 16 bytes if an IPv6 address-family. Map-Reply Record When the R bit is set, this field is the size of the "Record" field in the Map-Reply format. This Map-Reply record contains the EID-to-RLOC mapping entry associated with the Source EID. This allows the ETR which will receive this Map-Request to cache the data if it chooses to do so. Farinacci, et al. Expires April 13, 2009 [Page 25] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 Mapping Protocol Data: See [CONS] or [ALT] for details. 6.1.3. EID-to-RLOC UDP Map-Request Message A Map-Request is sent from an ITR when it needs a mapping for an EID, wants to test an RLOC for reachability, or wants to refresh a mapping before TTL expiration. This is performed by using the RLOC as the destination address for Map-Request message with a randomly allocated source UDP port number and the well-known destination port number 4342. A successful Map-Reply updates the cached set of RLOCs associated with the EID prefix range. Map-Requests MUST be rate-limited. It is recommended that a Map- Request for the same EID-prefix be sent no more than once per second. 6.1.4. Map-Reply Message Format +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |x|M| Locator Reach Bits | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Nonce | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Type=2 | Reserved | Record Count | +----> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Record TTL | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ R | Locator Count | EID mask-len |A| Reserved | e +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ c | Reserved | EID-AFI | o +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ r | EID-prefix | d +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | /| Priority | Weight | M Priority | M Weight | | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Loc | Unused Flags |R| Loc-AFI | | \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | \| Locator | +---> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Mapping Protocol Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Packet field descriptions: Farinacci, et al. Expires April 13, 2009 [Page 26] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 x: Set to 0 on transmission and ignored on receipt. Locator Reach Bits: Refer to Section 5.3. When there are multiple records in the Map-Reply message, this field is set to 0 and the R-bit for each Locator record within each mapping record is used to determine the locator reachability. Nonce: A 4-byte value set in a Data-Probe packet or a Map-Request that is echoed here in the Map-Reply. Type: 2 (Map-Reply) Reserved: Set to 0 on transmission and ignored on receipt. Record Count: The number of records in this reply message. A record is comprised of that portion of the packet labeled 'Record' above and occurs the number of times equal to Record count. If the record count is not 1 then the Locator Reach Bits field MUST be 0. Record TTL: The time in minutes the recipient of the Map-Reply will store the mapping. If the TTL is 0, the entry should be removed from the cache immediately. If the value is 0xffffffff, the recipient can decide locally how long to store the mapping. Locator Count: The number of Locator entries. A locator entry comprises what is labeled above as 'Loc'. The locator count can be 0 indicating there are no locators for the EID-prefix. EID mask-len: Mask length for EID prefix. A: The Authoritative bit, when sent by a UDP-based message is always set by the ETR. See [CONS] for TCP-based Map-Replies. EID-AFI: Address family of EID-prefix according to [RFC2434]. EID-prefix: 4 bytes if an IPv4 address-family, 16 bytes if an IPv6 address-family. Priority: each RLOC is assigned a unicast priority. Lower values are more preferable. When multiple RLOCs have the same priority, they may be used in a load-split fashion. A value of 255 means the RLOC MUST NOT be used for unicast forwarding. Weight: when priorities are the same for multiple RLOCs, the weight indicates how to balance unicast traffic between them. Weight is encoded as a percentage of total unicast packets that match the mapping entry. If a non-zero weight value is used for any RLOC, then all RLOCs must use a non-zero weight value and then the sum Farinacci, et al. Expires April 13, 2009 [Page 27] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 of all weight values MUST equal 100. If a zero value is used for any RLOC weight, then all weights MUST be zero and the receiver of the Map-Reply will decide how to load-split traffic. See Section 6.4 for a suggested hash algorithm to distribute load across locators with same priority and equal weight values. M Priority: each RLOC is assigned a multicast priority used by an ETR in a receiver multicast site to select an ITR in a source multicast site for building multicast distribution trees. A value of 255 means the RLOC MUST NOT be used for joining a multicast distribution tree. M Weight: when priorities are the same for multiple RLOCs, the weight indicates how to balance building multicast distribution trees across multiple ITRs. The weight is encoded as a percentage of total number of trees build to the source site identified by the EID-prefix. If a non-zero weight value is used for any RLOC, then all RLOCs must use a non-zero weight value and then the sum of all weight values MUST equal 100. If a zero value is used for any RLOC weight, then all weights MUST be zero and the receiver of the Map-Reply will decide how to distribute multicast state across ITRs. Unused Flags: set to 0 when sending and ignored on receipt. R: when this bit is set, the locator is known to be reachable from the Map-Reply sender's perspective. When there is a single mapping record in the message, the R-bit for each locator must have a consistent setting with the bitfield setting of the 'Loc Reach Bits' field in the early part of the header. When there are multiple mapping records in the message, the 'Loc Reach Bits' field is set to 0. Locator: an IPv4 or IPv6 address (as encoded by the 'Loc-AFI' field) assigned to an ETR or router acting as a proxy replier for the EID-prefix. Note that the destination RLOC address MAY be an anycast address. A source RLOC can be an anycast address as well. The source or destination RLOC MUST NOT be the broadcast address (255.255.255.255 or any subnet broadcast address known to the router), and MUST NOT be a link-local multicast address. The source RLOC MUST NOT be a multicast address. The destination RLOC SHOULD be a multicast address if it is being mapped from a multicast destination EID. Mapping Protocol Data: See [CONS] or [ALT] for details. Farinacci, et al. Expires April 13, 2009 [Page 28] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 6.1.5. EID-to-RLOC UDP Map-Reply Message When a Data Probe packet or a Map-Request triggers a Map-Reply to be sent, the RLOCs associated with the EID-prefix matched by the EID in the original packet destination IP address field will be returned. The RLOCs in the Map-Reply are the globally-routable IP addresses of the ETR but are not necessarily reachable; separate testing of reachability is required. Note that a Map-Reply may contain different EID-prefix granularity (prefix + length) than the Map-Request which triggers it. This might occur if a Map-Request were for a prefix that had been returned by an earlier Map-Reply. In such a case, the requester updates its cache with the new prefix information and granularity. For example, a requester with two cached EID-prefixes that are covered by a Map- Reply containing one, less-specific prefix, replaces the entry with the less-specific EID-prefix. Note that the reverse, replacement of one less-specific prefix with multiple more-specific prefixes, can also occur but not by removing the less-specific prefix rather by adding the more-specific prefixes which during a lookup will override the less-specific prefix. Replies SHOULD be sent for an EID-prefix no more often than once per second to the same requesting router. For scalability, it is expected that aggregation of EID addresses into EID-prefixes will allow one Map-Reply to satisfy a mapping for the EID addresses in the prefix range thereby reducing the number of Map-Request messages. The addresses for a encapsulated data packets or Map-Request message are swapped and used for sending the Map-Reply. The UDP source and destination ports are swapped as well. That is, the source port in the UDP header for the Map-Reply is set to the well-known UDP port number 4342. 6.2. Routing Locator Selection Both client-side and server-side may need control over the selection of RLOCs for conversations between them. This control is achieved by manipulating the Priority and Weight fields in EID-to-RLOC Map-Reply messages. Alternatively, RLOC information may be gleaned from received tunneled packets or EID-to-RLOC Map-Request messages. The following enumerates different scenarios for choosing RLOCs and the controls that are available: o Server-side returns one RLOC. Client-side can only use one RLOC. Server-side has complete control of the selection. Farinacci, et al. Expires April 13, 2009 [Page 29] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 o Server-side returns a list of RLOC where a subset of the list has the same best priority. Client can only use the subset list according to the weighting assigned by the server-side. In this case, the server-side controls both the subset list and load- splitting across its members. The client-side can use RLOCs outside of the subset list if it determines that the subset list is unreachable (unless RLOCs are set to a Priority of 255). Some sharing of control exists: the server-side determines the destination RLOC list and load distribution while the client-side has the option of using alternatives to this list if RLOCs in the list are unreachable. o Server-side sets weight of 0 for the RLOC subset list. In this case, the client-side can choose how the traffic load is spread across the subset list. Control is shared by the server-side determining the list and the client determining load distribution. Again, the client can use alternative RLOCs if the server-provided list of RLOCs are unreachable. o Either side (more likely on the server-side ETR) decides not to send a Map-Request. For example, if the server-side ETR does not send Map-Requests, it gleans RLOCs from the client-side ITR, giving the client-side ITR responsibility for bidirectional RLOC reachability and preferability. Server-side ETR gleaning of the client-side ITR RLOC is done by caching the inner header source EID and the outer header source RLOC of received packets. The client-side ITR controls how traffic is returned and can alternate using an outer header source RLOC, which then can be added to the list the server-side ETR uses to return traffic. Since no Priority or Weights are provided using this method, the server- side ETR must assume each client-side ITR RLOC uses the same best Priority with a Weight of zero. In addition, since EID-prefix encoding cannot be conveyed in data packets, the EID-to-RLOC cache on tunnel routers can grow to be very large. RLOCs that appear in EID-to-RLOC Map-Reply messages are considered reachable. The Map-Reply and the database mapping service does not provide any reachability status for Locators. This is done outside of the mapping service. See next section for details. 6.3. Routing Locator Reachability There are 4 methods for determining when a Locator is either reachable or has become unreachable: 1. Locator reachability is determined by an ETR by examining the Loc-Reach-Bits from a LISP header of a encapsulated data packet which is provided by an ITR when an ITR encapsulates data. Farinacci, et al. Expires April 13, 2009 [Page 30] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 2. Locator unreachability is determined by an ITR by receiving ICMP Network or Host Unreachable messages. 3. ETR unreachability is determined when a host sends an ICMP Port Unreachable message. 4. Locator reachability is determined by receiving a Map-Reply message from a ETR's Locator address in response to a previously sent Map-Request. When determining Locator reachability by examining the Loc-Reach-Bits from the LISP encapsulate data packet, an ETR will receive up to date status from the ITR closest to the Locators at the source site. The ITRs at the source site can determine reachability when running their IGP at the site. When the ITRs are deployed on CE routers, typically a default route is injected into the site's IGP from each of the ITRs. If an ITR goes down, the CE-PE link goes down, or the PE router goes down, the CE router withdraws the default route. This allows the other ITRs at the site to determine one of the Locators has gone unreachable. The Locators listed in a Map-Reply are numbered with ordinals 0 to n-1. The Loc-Reach-Bits in a LISP Data Message are numbered from 0 to n-1 starting with the least significant bit numbered as 0. So, for example, if the ITR with locator listed as the 3rd Locator position in the Map-Reply goes down, all other ITRs at the site will have the 3rd bit from the right cleared (the bit that corresponds to ordinal 2). When an ETR decapsulates a packet, it will look for a change in the Loc-Reach-Bits value. When a bit goes from 1 to 0, the ETR will refrain from encapsulating packets to the Locator that has just gone unreachable. It can start using the Locator again when the bit that corresponds to the Locator goes from 0 to 1. Loc-Reach-Bits are associated with a locator-set per EID-prefix. Therefore, when a locator becomes unreachable, the loc-reach-bit that corresponds to that locator's position in the list returned by the last Map-Reply will be set to zero for that particular EID-prefix. When ITRs at the site are not deployed in CE routers, the IGP can still be used to determine the reachability of Locators provided they are injected a stub links into the IGP. This is typically done when a /32 address is configured on a loopback interface. When ITRs receive ICMP Network or Host Unreachable messages as a method to determine unreachability, they will refrain from using Locators which are described in Locator lists of Map-Replies. However, using this approach is unreliable because many network Farinacci, et al. Expires April 13, 2009 [Page 31] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 operators turn off generation of ICMP Unreachable messages. If an ITR does receive an ICMP Network or Host Unreachable message, it MAY originate its own ICMP Unreachable message destined for the host that originated the data packet the ITR encapsulated. Optionally, an ITR can send a Map-Request to a Locator and if a Map- Reply is returned, reachability of the Locator has been determined. Obviously, sending such probes increases the number of control messages originated by tunnel routers for active flows, so Locators are assumed to be reachable when they are advertised. This assumption does create a dependency: Locator unreachability is detected by the receipt of ICMP Host Unreachable messages. When an Locator has been determined to be unreachable, it is not used for active traffic; this is the same as if it were listed in a Map-Reply with priority 255. The ITR can test the reachability of the unreachable Locator by sending periodic Requests. Both Requests and Replies MUST be rate- limited. Locator reachability testing is never done with data packets since that increases the risk of packet loss for end-to-end sessions. 6.4. Routing Locator Hashing When an ETR provides an EID-to-RLOC mapping in a Map-Reply message to a requesting ITR, the locator-set for the EID-prefix may contain different priority values for each locator address. When more than one best priority locator exists, the ITR can decide how to load share traffic against the corresponding locators. The following hash algorithm may be used by an ITR to select a locator for a packet destined to an EID for the EID-to-RLOC mapping: 1. Either a source and destination address hash can be used or the traditional 5-tuple hash which includes the source and destination addresses, source and destination TCP or UDP port numbers and the IP protocol number field or IPv6 next-protocol fields of a packet a host originates from within a LISP site. 2. Take the hash value and divide it by the number of locators stored in the locator-set for the EID-to-RLOC mapping. 3. The remainder will be yield a value of 0 to "number of locators minus 1". Use the remainder to select the locator in the locator-set. Farinacci, et al. Expires April 13, 2009 [Page 32] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 Note that when a packet is LISP encapsulated, the source port number in the outer UDP header needs to be set. Selecting a random value allows core routers which are attached to Link Aggregation Groups (LAGs) to load-split the encapsulated packets across member links of such LAGs. Otherwise, core routers would see a single flow, since packets have a source address of the ITR, for packets which are originated by different EIDs at the source site. A suggested setting for the source port number computed by an ITR is a 5-tuple hash function on the inner header, as described above. 6.5. Changing the Contents of EID-to-RLOC Mappings Since the LISP architecture uses a caching scheme to retrieve and store EID-to-RLOC mappings, the only way an ITR can get a more up-to- date mapping is to re-request the mapping. However, the ITRs do not know when the mappings change and the ETRs do not keep track of who requested its mappings. For scalability reasons, we want to maintain this approach but need to provide a way for ETRs change their mappings and inform the sites that are currently communicating with the ETR site using such mappings. When a locator record is added to the end of a locator-set, it is easy to update mappings. We assume new mappings will maintain the same locator ordering as the old mapping but just have new locators appended to the end of the list. So some ITRs can have a new mapping while other ITRs have only an old mapping that is used until they time out. When an ITR has only an old mapping but detects bits set in the loc-reach-bits that correspond to locators beyond the list it has cached, it simply ignores them. When a locator record is removed from a locator-set, ITRs that have the mapping cached will not use the removed locator because the xTRs will set the loc-reach-bit to 0. So even if the locator is in the list, it will not be used. For new mapping requests, the xTRs can set the locator address to 0 as well as setting the corresponding loc-reach-bit to 0. This forces ITRs with old or new mappings to avoid using the removed locator. If many changes occur to a mapping over a long period of time, one will find empty record slots in the middle of the locator-set and new records appended to the locator-set. At some point, it would be useful to compact the locator-set so the loc-reach-bit settings can be efficiently packed. We propose here two approaches for locator-set compaction, one operational and the other a protocol mechanism. The operational approach uses a clock sweep method. The protocol approach uses the concept of Solicit-Map-Requests. Farinacci, et al. Expires April 13, 2009 [Page 33] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 6.5.1. Clock Sweep The clock sweep approach uses planning in advance and the use of count-down TTLs to time out mappings that have already been cached. The default setting for an EID-to-RLOC mapping TTL is 24 hours. So there is a 24 hour window to time out old mappings. The following clock sweep procedure is used: 1. 24 hours before a mapping change is to take effect, a network administrator configures the ETRs at a site to start the clock sweep window. 2. During the clock sweep window, ETRs continue to send Map-Reply messages with the current (unchanged) mapping records. The TTL for these mappings is set to 1 hour. 3. 24 hours later, all previous cache entries will have timed out, and any active cache entries will time out within 1 hour. During this 1 hour window the ETRs continue to send Map-Reply messages with the current (unchanged) mapping records with the TTL set to 1 minute. 4. At the end of the 1 hour window, the ETRs will send Map-Reply messages with the new (changed) mapping records. So any active caches can get the new mapping contents right away if not cached, or in 1 minute if they had the mapping cached. 6.5.2. Solicit-Map-Request (SMR) Soliciting a Map-Request is a selective way for xTRs, at the site where mappings change, to control the rate they receive requests for Map-Reply messages. SMRs are also used to tell remote ITRs to update the mappings they have cached. Since the xTRs don't keep track of remote ITRs that have cached their mappings, they can not tell exactly who needs the new mapping entries. So an xTR will solicit Map-Requests from sites it is currently sending encapsulated data to, and only from those sites. The xTRs can locally decide the algorithm for how often and to how many sites it sends SMR messages. An SMR message is simply a bit set in an encapsulated data packet (and a Map-Request message). When an ETR at a remote site decapsulates a data packet that has the SMR bit set, it can tell that a new Map-Request message is being solicited. Both the xTR that sends the SMR message and the site that acts on the SMR message MUST be rate-limited. Farinacci, et al. Expires April 13, 2009 [Page 34] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 The following procedure shows how a SMR exchange occurs when a site is doing locator-set compaction for an EID-to-RLOC mapping: 1. When the database mappings in an ETR change, the ITRs at the site begin to set the SMR bit in packets they encapsulate to the sites they communicate with. 2. A remote xTR which decapsulates a packet with the SMR bit set will schedule sending a Map-Request message to the source locator address of the encapsulated packet. The nonce in the Map-Request is copied from the nonce in the encapsulated data packet that has the SMR bit set. 3. The remote xTR retransmits the Map-Request slowly until it gets a Map-Reply while continuing to use the cached mapping. 4. The ETRs at the site with the changed mapping will reply to the Map-Request with a Map-Reply message provided the Map-Request nonce matches the nonce from the SMR. The Map-Reply messages SHOULD be rate limited. This is important to avoid Map-Reply implosion. 5. The ETRs, at the site with the changed mapping, records the fact that the site that sent the Map-Request has received the new mapping data in the mapping cache entry for the remote site so the loc-reach-bits are reflective of the new mapping for packets going to the remote site. Farinacci, et al. Expires April 13, 2009 [Page 35] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 7. Router Performance Considerations LISP is designed to be very hardware-based forwarding friendly. By doing tunnel header prepending [RFC1955] and stripping instead of re- writing addresses, existing hardware can support the forwarding model with little or no modification. Where modifications are required, they should be limited to re-programming existing hardware rather than requiring expensive design changes to hard-coded algorithms in silicon. A few implementation techniques can be used to incrementally implement LISP: o When a tunnel encapsulated packet is received by an ETR, the outer destination address may not be the address of the router. This makes it challenging for the control plane to get packets from the hardware. This may be mitigated by creating special FIB entries for the EID-prefixes of EIDs served by the ETR (those for which the router provides an RLOC translation). These FIB entries are marked with a flag indicating that control plane processing should be performed. The forwarding logic of testing for particular IP protocol number value is not necessary. No changes to existing, deployed hardware should be needed to support this. o On an ITR, prepending a new IP header is as simple as adding more bytes to a MAC rewrite string and prepending the string as part of the outgoing encapsulation procedure. Many routers that support GRE tunneling [RFC2784] or 6to4 tunneling [RFC3056] can already support this action. o When a received packet's outer destination address contains an EID which is not intended to be forwarded on the routable topology (i.e. LISP 1.5), the source address of a data packet or the router interface with which the source is associated (the interface from which it was received) can be associated with a VRF (Virtual Routing/Forwarding), in which a different (i.e. non- congruent) topology can be used to find EID-to-RLOC mappings. Farinacci, et al. Expires April 13, 2009 [Page 36] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 8. Deployment Scenarios This section will explore how and where ITRs and ETRs can be deployed and will discuss the pros and cons of each deployment scenario. There are two basic deployment trade-offs to consider: centralized versus distributed caches and flat, recursive, or re-encapsulating tunneling. When deciding on centralized versus distributed caching, the following issues should be considered: o Are the tunnel routers spread out so that the caches are spread across all the memories of each router? o Should management "touch points" be minimized by choosing few tunnel routers, just enough for redundancy? o In general, using more ITRs doesn't increase management load, since caches are built and stored dynamically. On the other hand, more ETRs does require more management since EID-prefix-to-RLOC mappings need to be explicitly configured. When deciding on flat, recursive, or re-encapsulation tunneling, the following issues should be considered: o Flat tunneling implements a single tunnel between source site and destination site. This generally offers better paths between sources and destinations with a single tunnel path. o Recursive tunneling is when tunneled traffic is again further encapsulated in another tunnel, either to implement VPNs or to perform Traffic Engineering. When doing VPN-based tunneling, the site has some control since the site is prepending a new tunnel header. In the case of TE-based tunneling, the site may have control if it is prepending a new tunnel header, but if the site's ISP is doing the TE, then the site has no control. Recursive tunneling generally will result in suboptimal paths but at the benefit of steering traffic to resource available parts of the network. o The technique of re-encapsulation ensures that packets only require one tunnel header. So if a packet needs to be rerouted, it is first decapsulated by the ETR and then re-encapsulated with a new tunnel header using a new RLOC. The next sub-sections will describe where tunnel routers can reside in the network. Farinacci, et al. Expires April 13, 2009 [Page 37] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 8.1. First-hop/Last-hop Tunnel Routers By locating tunnel routers close to hosts, the EID-prefix set is at the granularity of an IP subnet. So at the expense of more EID- prefix-to-RLOC sets for the site, the caches in each tunnel router can remain relatively small. But caches always depend on the number of non-aggregated EID destination flows active through these tunnel routers. With more tunnel routers doing encapsulation, the increase in control traffic grows as well: since the EID-granularity is greater, more Map-Requests and Map-Replies are traveling between more routers. The advantage of placing the caches and databases at these stub routers is that the products deployed in this part of the network have better price-memory ratios then their core router counterparts. Memory is typically less expensive in these devices and fewer routes are stored (only IGP routes). These devices tend to have excess capacity, both for forwarding and routing state. LISP functionality can also be deployed in edge switches. These devices generally have layer-2 ports facing hosts and layer-3 ports facing the Internet. Spare capacity is also often available in these devices as well. 8.2. Border/Edge Tunnel Routers Using customer-edge (CE) routers for tunnel endpoints allows the EID space associated with a site to be reachable via a small set of RLOCs assigned to the CE routers for that site. This offers the opposite benefit of the first-hop/last-hop tunnel router scenario: the number of mapping entries and network management touch points are reduced, allowing better scaling. One disadvantage is that less of the network's resources are used to reach host endpoints thereby centralizing the point-of-failure domain and creating network choke points at the CE router. Note that more than one CE router at a site can be configured with the same IP address. In this case an RLOC is an anycast address. This allows resilience between the CE routers. That is, if a CE router fails, traffic is automatically routed to the other routers using the same anycast address. However, this comes with the disadvantage where the site cannot control the entrance point when the anycast route is advertised out from all border routers. Farinacci, et al. Expires April 13, 2009 [Page 38] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 8.3. ISP Provider-Edge (PE) Tunnel Routers Use of ISP PE routers as tunnel endpoint routers gives an ISP control over the location of the egress tunnel endpoints. That is, the ISP can decide if the tunnel endpoints are in the destination site (in either CE routers or last-hop routers within a site) or at other PE edges. The advantage of this case is that two or more tunnel headers can be avoided. By having the PE be the first router on the path to encapsulate, it can choose a TE path first, and the ETR can decapsulate and re-encapsulate for a tunnel to the destination end site. An obvious disadvantage is that the end site has no control over where its packets flow or the RLOCs used. As mentioned in earlier sections a combination of these scenarios is possible at the expense of extra packet header overhead, if both site and provider want control, then recursive or re-encapsulating tunnels are used. Farinacci, et al. Expires April 13, 2009 [Page 39] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 9. Mobility Considerations There are several kinds of mobility of which only some might be of concern to LISP. Essentially they are as follows. 9.1. Site Mobility A site wishes to change its attachment points to the Internet, and its LISP Tunnel Routers will have new RLOCs when it changes upstream providers. Changes in EID-RLOC mappings for sites are expected to be handled by configuration, outside of the LISP protocol. 9.2. Slow Endpoint Mobility An individual endpoint wishes to move, but is not concerned about maintaining session continuity. Renumbering is involved. LISP can help with the issues surrounding renumbering [RFC4192] [LISA96] by decoupling the address space used by a site from the address spaces used by its ISPs. [RFC4984] 9.3. Fast Endpoint Mobility Fast endpoint mobility occurs when an endpoint moves relatively rapidly, changing its IP layer network attachment point. Maintenance of session continuity is a goal. This is where the Mobile IPv4 [RFC3344bis] and Mobile IPv6 [RFC3775] [RFC4866] mechanisms are used, and primarily where interactions with LISP need to be explored. The problem is that as an endpoint moves, it may require changes to the mapping between its EID and a set of RLOCs for its new network location. When this is added to the overhead of mobile IP binding updates, some packets might be delayed or dropped. In IPv4 mobility, when an endpoint is away from home, packets to it are encapsulated and forwarded via a home agent which resides in the home area the endpoint's address belongs to. The home agent will encapsulate and forward packets either directly to the endpoint or to a foreign agent which resides where the endpoint has moved to. Packets from the endpoint may be sent directly to the correspondent node, may be sent via the foreign agent, or may be reverse-tunneled back to the home agent for delivery to the mobile node. As the mobile node's EID or available RLOC changes, LISP EID-to-RLOC mappings are required for communication between the mobile node and the home agent, whether via foreign agent or not. As a mobile endpoint changes networks, up to three LISP mapping changes may be required: Farinacci, et al. Expires April 13, 2009 [Page 40] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 o The mobile node moves from an old location to a new visited network location and notifies its home agent that it has done so. The Mobile IPv4 control packets the mobile node sends pass through one of the new visited network's ITRs, which needs a EID-RLOC mapping for the home agent. o The home agent might not have the EID-RLOC mappings for the mobile node's "care-of" address or its foreign agent in the new visited network, in which case it will need to acquire them. o When packets are sent directly to the correspondent node, it may be that no traffic has been sent from the new visited network to the correspondent node's network, and the new visited network's ITR will need to obtain an EID-RLOC mapping for the correspondent node's site. In addition, if the IPv4 endpoint is sending packets from the new visited network using its original EID, then LISP will need to perform a route-returnability check on the new EID-RLOC mapping for that EID. In IPv6 mobility, packets can flow directly between the mobile node and the correspondent node in either direction. The mobile node uses its "care-of" address (EID). In this case, the route-returnability check would not be needed but one more LISP mapping lookup may be required instead: o As above, three mapping changes may be needed for the mobile node to communicate with its home agent and to send packets to the correspondent node. o In addition, another mapping will be needed in the correspondent node's ITR, in order for the correspondent node to send packets to the mobile node's "care-of" address (EID) at the new network location. When both endpoints are mobile the number of potential mapping lookups increases accordingly. As a mobile node moves there are not only mobility state changes in the mobile node, correspondent node, and home agent, but also state changes in the ITRs and ETRs for at least some EID-prefixes. The goal is to support rapid adaptation, with little delay or packet loss for the entire system. Heuristics can be added to LISP to reduce the number of mapping changes required and to reduce the delay per mapping change. Also IP mobility can be modified to require fewer mapping changes. In order to increase overall system Farinacci, et al. Expires April 13, 2009 [Page 41] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 performance, there may be a need to reduce the optimization of one area in order to place fewer demands on another. In LISP, one possibility is to "glean" information. When a packet arrives, the ETR could examine the EID-RLOC mapping and use that mapping for all outgoing traffic to that EID. It can do this after performing a route-returnability check, to ensure that the new network location does have a internal route to that endpoint. However, this does not cover the case where an ITR (the node assigned the RLOC) at the mobile-node location has been compromised. Mobile IP packet exchange is designed for an environment in which all routing information is disseminated before packets can be forwarded. In order to allow the Internet to grow to support expected future use, we are moving to an environment where some information may have to be obtained after packets are in flight. Modifications to IP mobility should be considered in order to optimize the behavior of the overall system. Anything which decreases the number of new EID- RLOC mappings needed when a node moves, or maintains the validity of an EID-RLOC mapping for a longer time, is useful. 9.4. Fast Network Mobility In addition to endpoints, a network can be mobile, possibly changing xTRs. A "network" can be as small as a single router and as large as a whole site. This is different from site mobility in that it is fast and possibly short-lived, but different from endpoint mobility in that a whole prefix is changing RLOCs. However, the mechanisms are the same and there is no new overhead in LISP. A map request for any endpoint will return a binding for the entire mobile prefix. If mobile networks become a more common occurrence, it may be useful to revisit the design of the mapping service and allow for dynamic updates of the database. The issue of interactions between mobility and LISP needs to be explored further. Specific improvements to the entire system will depend on the details of mapping mechanisms. Mapping mechanisms should be evaluated on how well they support session continuity for mobile nodes. Farinacci, et al. Expires April 13, 2009 [Page 42] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 10. Multicast Considerations A multicast group address, as defined in the original Internet architecture is an identifier of a grouping of topologically independent receiver host locations. The address encoding itself does not determine the location of the receiver(s). The multicast routing protocol, and the network-based state the protocol creates, determines where the receivers are located. In the context of LISP, a multicast group address is both an EID and a Routing Locator. Therefore, no specific semantic or action needs to be taken for a destination address, as it would appear in an IP header. Therefore, a group address that appears in an inner IP header built by a source host will be used as the destination EID. The outer IP header (the destination Routing Locator address), prepended by a LISP router, will use the same group address as the destination Routing Locator. Having said that, only the source EID and source Routing Locator needs to be dealt with. Therefore, an ITR merely needs to put its own IP address in the source Routing Locator field when prepending the outer IP header. This source Routing Locator address, like any other Routing Locator address MUST be globally routable. Therefore, an EID-to-RLOC mapping does not need to be performed by an ITR when a received data packet is a multicast data packet or when processing a source-specific Join (either by IGMPv3 or PIM). But the source Routing Locator is decided by the multicast routing protocol in a receiver site. That is, an EID to Routing Locator translation is done at control-time. Another approach is to have the ITR not encapsulate a multicast packet and allow the the host built packet to flow into the core even if the source address is allocated out of the EID namespace. If the RPF-Vector TLV [RPFV] is used by PIM in the core, then core routers can RPF to the ITR (the Locator address which is injected into core routing) rather than the host source address (the EID address which is not injected into core routing). To avoid any EID-based multicast state in the network core, the first approach is chosen for LISP-Multicast. Details for LISP-Multicast and Interworking with non-LISP sites is described in specification [MLISP]. Farinacci, et al. Expires April 13, 2009 [Page 43] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 11. Security Considerations It is believed that most of the security mechanisms will be part of the mapping database service when using control plane procedures for obtaining EID-to-RLOC mappings. For data plane triggered mappings, as described in this specification, protection is provided against ETR spoofing by using Return- Routability mechanisms evidenced by the use of a 4-byte Nonce field in the LISP encapsulation header. The nonce, coupled with the ITR accepting only solicited Map-Replies goes a long way toward providing decent authentication. LISP does not rely on a PKI infrastructure or a more heavy weight authentication system. These systems challenge the scalability of LISP which was a primary design goal. DoS attack prevention will depend on implementations rate-limiting Map-Requests and Map-Replies to the control plane as well as rate- limiting the number of data-triggered Map-Replies. Farinacci, et al. Expires April 13, 2009 [Page 44] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 12. Prototype Plans and Status The operator community has requested that the IETF take a practical approach to solving the scaling problems associated with global routing state growth. This document offers a simple solution which is intended for use in a pilot program to gain experience in working on this problem. The authors hope that publishing this specification will allow the rapid implementation of multiple vendor prototypes and deployment on a small scale. Doing this will help the community: o Decide whether a new EID-to-RLOC mapping database infrastructure is needed or if a simple, UDP-based, data-triggered approach is flexible and robust enough. o Experiment with provider-independent assignment of EIDs while at the same time decreasing the size of DFZ routing tables through the use of topologically-aligned, provider-based RLOCs. o Determine whether multiple levels of tunneling can be used by ISPs to achieve their Traffic Engineering goals while simultaneously removing the more specific routes currently injected into the global routing system for this purpose. o Experiment with mobility to determine if both acceptable convergence and session continuity properties can be scalably implemented to support both individual device roaming and site service provider changes. Here is a rough set of milestones: 1. This draft will be the draft for interoperable implementations to code against. Interoperable implementations will be ready Fall of 2008. 2. Continue pilot deployment summer of 2008 using LISP-ALT as the database mapping mechanism. 3. Continue prototyping other database lookup schemes, be it DNS, DHTs, CONS, ALT, NERD, or other mechanisms. 4. Implement the LISP Multicast draft [MLISP]. 5. Research more on how policy affects what gets returned in a Map- Reply from an ETR. Farinacci, et al. Expires April 13, 2009 [Page 45] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 6. Continue to experiment with mixed locator-sets to understand how LISP can help the IPv4 to IPv6 transition. As of this writing the following accomplishments have been achieved: 1. A unit- and system-tested software switching implementation has been completed on cisco NX-OS for this draft for both IPv4 and IPv6 EIDs using a mixed locator-set of IPv4 and IPv6 locators. 2. A unit- and system-tested software switching implementation on cisco NX-OS has been completed for draft for [ALT]. 3. A unit- and system-tested software switching implementation on cisco NX-OS has been completed for draft [INTERWORK]. Support for IPv4 translation is provided and PTR support for IPv4 and IPv6 is provided. 4. The cisco NX-OS implementation supports an experimental mechanism for slow mobility. 5. Dave Meyer, Vince Fuller, Darrel Lewis, Greg Shepherd, and Andrew Partan continue to test all the features described above on a dual-stack infrastructure. 6. Darrel Lewis and Dave Meyer have deployed both LISP translation and LISP PTR support in the pilot network. Point your browser to http://www.lisp4.net to see translation happening in action so your non-LISP site can access a web server in a LISP site. 7. Soon http://www.lisp6.net will work where your IPv6 LISP site can talk to a IPv6 web server in a LISP site by using mixed address- family based locators. 8. An public domain implementation of LISP is underway. See [OPENLISP] for details. 9. A cisco IOS implementation is underway which currently supports IPv4 encapsulation and decapsulation features. If interested in writing a LISP implementation, testing any of the LISP implementations, or want to be part of the LISP pilot program, please contact: lisp-interest@lists.civil-tongue.net Farinacci, et al. Expires April 13, 2009 [Page 46] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 13. References 13.1. Normative References [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August 1980. [RFC1498] Saltzer, J., "On the Naming and Binding of Network Destinations", RFC 1498, August 1993. [RFC1955] Hinden, R., "New Scheme for Internet Routing and Addressing (ENCAPS) for IPNG", RFC 1955, June 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, March 2000. [RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains via IPv4 Clouds", RFC 3056, February 2001. [RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004. [RFC4423] Moskowitz, R. and P. Nikander, "Host Identity Protocol (HIP) Architecture", RFC 4423, May 2006. [RFC4866] Arkko, J., Vogt, C., and W. Haddad, "Enhanced Route Optimization for Mobile IPv6", RFC 4866, May 2007. [RFC4984] Meyer, D., Zhang, L., and K. Fall, "Report from the IAB Workshop on Routing and Addressing", RFC 4984, September 2007. 13.2. Informative References [AFI] IANA, "Address Family Indicators (AFIs)", ADDRESS FAMILY NUMBERS http://www.iana.org/numbers.html, Febuary 2007. [ALT] Farinacci, D., Fuller, V., and D. Meyer, "LISP Alternative Topology (LISP-ALT)", draft-fuller-lisp-alt-03.txt (work in progress), April 2008. Farinacci, et al. Expires April 13, 2009 [Page 47] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 [APT] Jen, D., Meisel, M., Massey, D., Wang, L., Zhang, B., and L. Zhang, "APT: A Practical Transit Mapping Service", draft-jen-apt-00.txt (work in progress), July 2007. [CHIAPPA] Chiappa, J., "Endpoints and Endpoint names: A Proposed Enhancement to the Internet Architecture", Internet- Draft http://www.chiappa.net/~jnc/tech/endpoints.txt, 1999. [CONS] Farinacci, D., Fuller, V., and D. Meyer, "LISP-CONS: A Content distribution Overlay Network Service for LISP", draft-meyer-lisp-cons-03.txt (work in progress), November 2007. [DHTs] Ratnasamy, S., Shenker, S., and I. Stoica, "Routing Algorithms for DHTs: Some Open Questions", PDF file http://www.cs.rice.edu/Conferences/IPTPS02/174.pdf. [GSE] "GSE - An Alternate Addressing Architecture for IPv6", draft-ietf-ipngwg-gseaddr-00.txt (work in progress), 1997. [INTERWORK] Lewis, D., Meyer, D., and D. Farinacci, "Interworking LISP with IPv4 and IPv6", draft-lewis-lisp-interworking-01.txt (work in progress), July 2008. [LISA96] Lear, E., Katinsky, J., Coffin, J., and D. Tharp, "Renumbering: Threat or Menace?", Usenix , September 1996. [LISP1] Farinacci, D., Oran, D., Fuller, V., and J. Schiller, "Locator/ID Separation Protocol (LISP1) [Routable ID Version]", Slide-set http://www.dinof.net/~dino/ietf/lisp1.ppt, October 2006. [LISP2] Farinacci, D., Oran, D., Fuller, V., and J. Schiller, "Locator/ID Separation Protocol (LISP2) [DNS-based Version]", Slide-set http://www.dinof.net/~dino/ietf/lisp2.ppt, November 2006. [LISPDHT] Mathy, L., Iannone, L., and O. Bonaventure, "LISP-DHT: Towards a DHT to map identifiers onto locators", draft-mathy-lisp-dht-00.txt (work in progress), February 2008. [MLISP] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, "LISP for Multicast Environments", Farinacci, et al. Expires April 13, 2009 [Page 48] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 draft-farinacci-lisp-multicast-00.txt (work in progress), April 2008. [NERD] Lear, E., "NERD: A Not-so-novel EID to RLOC Database", draft-lear-lisp-nerd-02.txt (work in progress), January 2008. [OPENLISP] Iannone, L. and O. Bonaventure, "OpenLISP Implementation Report", draft-iannone-openlisp-implementation-00.txt (work in progress), February 2008. [RADIR] Narten, T., "Routing and Addressing Problem Statement", draft-narten-radir-problem-statement-00.txt (work in progress), July 2007. [RFC3344bis] Perkins, C., "IP Mobility Support for IPv4, revised", draft-ietf-mip4-rfc3344bis-05 (work in progress), July 2007. [RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for Renumbering an IPv6 Network without a Flag Day", RFC 4192, September 2005. [RPFV] Wijnands, IJ., Boers, A., and E. Rosen, "The RPF Vector TLV", draft-ietf-pim-rpf-vector-03.txt (work in progress), October 2006. [RPMD] Handley, M., Huici, F., and A. Greenhalgh, "RPMD: Protocol for Routing Protocol Meta-data Dissemination", draft-handley-p2ppush-unpublished-2007726.txt (work in progress), July 2007. [SHIM6] Nordmark, E. and M. Bagnulo, "Level 3 multihoming shim protocol", draft-ietf-shim6-proto-06.txt (work in progress), October 2006. Farinacci, et al. Expires April 13, 2009 [Page 49] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 Appendix A. Acknowledgments The authors would like to gratefully acknowledge many people who have contributed discussion and ideas to the making of this proposal. They include Jason Schiller, Lixia Zhang, Dorian Kim, Peter Schoenmaker, Darrel Lewis, Vijay Gill, Geoff Huston, David Conrad, Mark Handley, Ron Bonica, Ted Seely, Mark Townsley, Chris Morrow, Brian Weis, Dave McGrew, Peter Lothberg, Dave Thaler, Eliot Lear, Shane Amante, Ved Kafle, Olivier Bonaventure, Luigi Iannone, Robin Whittle, Brian Carpenter, Joel Halpern, Roger Jorgensen, John Zwiebel, Ran Atkinson, Stig Venaas, Iljitsch van Beijnum, Roland Bless, Andrew Partan, Dana Blair, Bill Lynch, Marc Woolward, Damien Saucez, and Damian Lezama. In particular, we would like to thank Dave Meyer for his clever suggestion for the name "LISP". ;-) Farinacci, et al. Expires April 13, 2009 [Page 50] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 Authors' Addresses Dino Farinacci cisco Systems Tasman Drive San Jose, CA 95134 USA Email: dino@cisco.com Vince Fuller cisco Systems Tasman Drive San Jose, CA 95134 USA Email: vaf@cisco.com Dave Oran cisco Systems 7 Ladyslipper Lane Acton, MA USA Email: oran@cisco.com Dave Meyer cisco Systems 170 Tasman Drive San Jose, CA USA Email: dmm@cisco.com Scott Brim cisco Systems 170 Tasman Drive San Jose, CA USA Email: sbrim@cisco.com Farinacci, et al. Expires April 13, 2009 [Page 51] Internet-Draft Locator/ID Separation Protocol (LISP) October 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Farinacci, et al. Expires April 13, 2009 [Page 52]