Dhcp Relay Agent On Acx Series Routers - Juniper ACX1000 Configuration Manual

ACX Series Universal Access Router Configuration Guide

DHCP Relay Agent on ACX Series Routers

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You can configure extended DHCP relay options on the ACX Series router and enable
the router to function as a DHCP relay agent. A DHCP relay agent forwards DHCP request
and reply packets between a DHCP client and a DHCP server. DHCP relay agents are
used to forward requests and replies between clients and servers that do not reside in
the same physical subnet. The forwarding of DHCP packets that the DHCP relay agent
performs differs from the normal forwarding of IP packets that a router performs. Unlike
IP forwarding in which IP datagrams are switched between networks in a slightly
transparent manner, a DHCP relay agent receives DHCP messages and generates a new
DHCP message to send out on another interface. The DHCP relay agent sets the gateway
address (giaddr field of the DHCP packet), adds the DHCP relay agent information option
(option 82) in the packet, if it is present, and forwards it to the DHCP server.
The DHCP relay agent information option (option 82) enables you to include additional
useful information in the client-originated DHCP packets that the DHCP relay forwards
to a DHCP server. When the DHCP relay agent information option is enabled, the DHCP
relay adds the option 82 information to packets it receives from clients, then forwards
the packets to the DHCP server. The DHCP server uses the option 82 information to
decide which IP address to assign to the client—the DHCP server might also use
information in the option 82 field for additional purposes, such as determining which
services to grant to the client. The DHCP server sends its reply back to the DHCP relay,
which removes the option 82 information field from the message, and then forwards the
packet to the client.
DHCP relay agents eliminate the need to configure a DHCP server in each physical network.
In mobile backhaul networks, most of the base station vendors might use DHCP as the
address assignment protocol for different types of base stations (for example, base
transceiver station (BTS) in 2G, NodeB in 3G, and eNodeB in 4G networks). In such
networks, you can configure ACX Series routers to operate as a DHCP relay agent to
forward DHCP requests and acknowledgements between the base station and the DHCP
server.
To configure the DHCP relay agent on the router for IPv4 packets, include the
statement at the
[edit forwarding-options]
dhcp-relay statement at the
hierarchy level.
forwarding-options]
NOTE: DHCP relay is supported on Integrated Routing and Bridging (IRB)
interfaces.
To verify and manage DHCP relay agent settings: you can use the following operational
commands:
clear dhcp relay binding
clear dhcp relay statistics
hierarchy level. You can also include the
[edit routing-instances routing-instance-name
dhcp-relay
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