Chapter 20 Configuring Dhcp Relay; Configuring Dhcp Relay And Bootp Relay - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - BROADBAND ACCESS CONFIGURATION GUIDE 2010-10-12 Configuration Manual

CHAPTER 20
Configuring DHCP Relay

Configuring DHCP Relay and BOOTP Relay

Copyright © 2010, Juniper Networks, Inc.
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 491
Rate of DHCP Client Packets Processed by DHCP Relay Overview on page 514
Configuring the Rate of Client Packets Processed by DHCP Relay on page 515
Configuring DHCP Relay Proxy on page 515
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
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