Dynamic Host Configuration Protocol
(DHCP) relay agent
dhcrelay utility 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.
dhcrelay listens for DHCP requests on a
given interface. When a query is received,
forwards it to the list of DHCP destinations specified on the command line.
When a reply is received, it is broadcast or unicast on the network from
whence the original request came.
The server might be a name, address or interface.
dhcrelay will operate in layer 2 mode when the
specified servers are interfaces, otherwise it will operate in layer 3
The name of at least one DHCP server to which DHCP and BOOTP
requests should be relayed, as well as the name of the network interface
dhcrelay should attempt to configure, must be
specified on the command line.
dhcrelay supports relaying of DHCP traffic
to configure IPsec tunnel mode clients when listening on the
using layer 3 mode only. The DHCP server has to support RFC 3046 to echo
back the relay agent information to allow stateless DHCP reply to IPsec
The options are as follows:
- The circuit-id relay agent information sub-option
dhcrelayshould append on relayed packets. If this option is not specified, it will use the interface number by default.
- Do not daemonize. If this option is specified,
dhcrelaywill run in the foreground and log to stderr.
- The name of the network interface that
dhcrelayshould attempt to configure. For layer 3 mode at least one IPv4 address has to be configured on this interface.
- Add the relay agent information option. By default, this is only enabled for the enc(4) interface.
- The remote-id relay agent information sub-option
dhcrelayshould append on relayed packets. If this option is not specified, it will use the destination address by default.
- Replace incoming Relay Agent Information with the one configured.
R. Droms, Dynamic Host Configuration Protocol, RFC 2131, March 1997.
S. Alexander and R. Droms, DHCP Options and BOOTP Vendor Extensions, RFC 2132, March 1997.
M. Patrick, DHCP Relay Agent Information Option, RFC 3046, January 2001.
B. Patel, B. Aboba, S. Kelly, and V. Gupta, Dynamic Host Configuration Protocol (DHCPv4) Configuration of IPsec Tunnel Mode, RFC 3456, January 2003.
dhcrelay was written by
The current implementation was reworked by Henning Brauer <firstname.lastname@example.org>.
Relayed DHCP traffic could actually safely be protected by IPsec
but, like dhcpd(8) and dhclient(8),
dhcrelay will bypass
IPsec for all its traffic.