Foundry NetIron M2404C and M2404F Metro Access Switches
Configuring DHCP Features (Rev. 03)
DHCP Relay
© 2008 Foundry Networks, Inc.
Page 43 of 63
DHCP Relay
The DHCP Relay Agent
The user can configure the device to act as a DHCP relay agent that will forward DHCP requests to
a server on another network and forward the replies back to the client.
A locally attached host can issue a DHCP request as a broadcast message. When the device
receives the broadcast message, it relays the message to the specified DHCP server.
The user should configure the device to perform as a DHCP relay agent in case the user has locally
attached hosts and the server is on a different subnet.
Figure 8: DHCP Relay Example
NOTE
When a super VLAN user port is configured on the relay agent, DHCP client
packets will only be relayed if the following access list has been configured:
access-list <
Number of Extended Access List
> permit udp any any eq bootps.
The access list should be applied on the user port or VLAN.
DHCP Option 82 Support
The DHCP relay agent information option (option 82) enables a DHCP relay agent to include
information about itself when forwarding client-originated DHCP packets to a DHCP server. The
DHCP server can use this information to implement an IP address or other parameter-assignment
policies.
Figure 9
shows a typical network topology in which DHCP is used. The aggregation
router also serves as the DHCP relay agent.
Figure 9: Network Topology Using DHCP