dhcrelay - Dynamic Host Configuration Protocol Relay Agent

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

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

The DHCP Relay Agent listens for DHCP requests on all interfaces attached to a host, unless one or more interfaces 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 network 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 solution.

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, eliminating non-broadcast interfaces if possible, 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 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.

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

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.