Chapter 20 Configuring Dhcp Relay - Juniper JUNOSE 11.1.X - BROADBAND ACCESS CONFIGURATION GUIDE 6-4-2010 Configuration Manual

Chapter 20
Configuring DHCP Relay
Configuring DHCP Relay and BOOTP Relay
The Dynamic Host Configuration Protocol (DHCP) provides a mechanism through
which computers using Transmission Control Protocol/IP (TCP/IP) can obtain protocol
configuration parameters automatically from a DHCP server on the network.
The following sections describe how to configure your E Series router to provide
DHCP support:
Configuring DHCP Relay and BOOTP Relay on page 495
Configuring DHCP Relay Proxy on page 518
The DHCP relay feature relays a request from a remote client to a DHCP server for
an IP address. When the router receives a DHCP request from an IP client, it forwards
the request to the DHCP server and passes the response back to the IP client.
Configuring DHCP relay also enables bootstrap protocol (BOOTP) relay. The router
relays any BOOTP requests it receives to the same set of servers that you configured
for DHCP relay. A DHCP server can respond to the BOOTP request only if it is also
a BOOTP server. The router relays any BOOTP responses it receives to the originator
of the BOOTP request. If you do not configure DHCP relay, then BOOTP relay is
disabled.
The router must wait for an acknowledgment from the DHCP server that the assigned
address has been accepted. The IP client must accept an IP address from one of the
servers. When the DHCP server sends an acknowledgment message back to the
DHCP client via the router, the router updates its routing table with the IP address
of the client.
If a DHCP relay request is received on an unnumbered interface, the router determines
the loopback address for that interface and passes that IP address to the server.
DHCP carries other important configuration parameters, such as the subnet mask,
default router, and DNS server. You can also use the DHCP relay agent information
option (option 82) to add information to the DHCP packets sent to DHCP servers the
additional information, in the form of suboptions to the option 82 value, helps you
to manage the IP address and service level assignments granted to your subscribers.
For example, you can add the E Series hostname or the virtual router name to the
front of the Agent Circuit ID suboption (suboption 1) of the DHCP relay agent
information option (option 82). See "Configuring Relay Agent Option 82 Information"
on page 506.
Configuring DHCP Relay and BOOTP Relay
495