


dhcrelay(8)                                           dhcrelay(8)


NAME
       dhcrelay - Dynamic Host Configuration Protocol Relay Agent

SYNOPSIS
       dhcrelay [ -p port ] [ -d ] [ -q ] [ -i if0 [ ...  -i  ifN
       ] ] server0 [ ...serverN ]

DESCRIPTION
       The  Internet Software Consortium DHCP Relay Agent, dhcre-
       lay, provides a means for relaying DHCP and BOOTP requests
       from  a  subnet  to  which no DHCP server is directly con-
       nected to one or more DHCP servers on other subnets.

OPERATION
       The DHCP Relay Agent listens  for  DHCP  requests  on  all
       interfaces  attached  to a host, unless one or more inter-
       faces are specified on the command line with the -i  flag.

       When a query is received, dhcrelay forwards it to the list
       of DHCP servers specified on the command  line.    When  a
       reply  is received, it is broadcast or unicast on the net-
       work from whence the original request came.

       It is possible to specify a set  of  interfaces  on  which
       dhcrelay  will  listen,  so  that if dhcrelay is connected
       through one interface to a network on which  there  is  no
       DHCP  server,  but  is connected on another interface to a
       network on which there is a DHCP server, it will not relay
       DHCP  and  BOOTP  requests  from  the network on which the
       server exists to that server.   This is an imperfect solu-
       tion.

COMMAND LINE
       The  names  of the network interfaces that dhcrelay should
       attempt to configure may be specified on the command  line
       using  the -i option.  If no interface names are specified
       on the command line dhcrelay  will  identify  all  network
       interfaces, elimininating non-broadcast interfaces if pos-
       sible, and attempt to configure each interface.

       If dhcrelay should listen and transmit  on  a  port  other
       than  the  standard  (port  67), the -p flag may used.  It
       should be followed by the udp port  number  that  dhcrelay
       should use.  This is mostly useful for debugging purposes.
       If the -p flag is specified, the relay agent will transmit
       responses  to clients at a port number that is one greater
       than the one specified - i.e., if you specify -p 67,  then
       the  relay  agent  will  listen on port 67 and transmit to
       port 68.   Transmissions to servers will be  sent  to  the
       same port number that it specified in the -p flag.

       Dhcrelay  will normally run in the foreground until it has
       configured an interface, and then will revert  to  running
       in the background.  To run force dhcrelay to always run as



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dhcrelay(8)                                           dhcrelay(8)


       a foreground process, the -d  flag  should  be  specified.
       This  is useful when running dhcrelay under a debugger, or
       when running it out of inittab on System V systems.

       Dhcrelay will normally print its network configuration  on
       startup.   This can be annoying in a system startup script
       - to disable this behaviour, specify the -q flag.

       The name of at least one DHCP server  to  which  DHCP  and
       BOOTP  requests should be relayed must be specified on the
       command line.


SEE ALSO
       dhclient(8), dhcpd(8), RFC2132, RFC2131.

BUGS
       Relayed DHCP traffic could actually safely be protected by
       IPsec, but like dhcpd(8) and dhclient(8), dhcrelay(8) will
       bypass IPsec for all its traffic.

AUTHOR
       dhcrelay(8) has been written  for  the  Internet  Software
       Consortium  by Ted Lemon <mellon@fugue.com> in cooperation
       with Vixie Enterprises.  To learn more about the  Internet
       Software Consortium, see http://www.vix.com/isc.  To learn
       more about Vixie Enterprises, see http://www.vix.com.






























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