Extreme Networks ExtremeWare XOS 11.3, Manual

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IPv4 Unicast Routing
ExtremeWare XOS 11.3 Concepts Guide
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Configuring the DHCP Relay Agent Option (Option 82)
After configuring and enabling the DHCP/BOOTP relay feature, you can enable the DHCP relay agent
option feature. This feature inserts a piece of information, called option 82, into any DHCP request
packet that is to be relayed by the switch. Similarly, if a DHCP reply received by the switch contains a
valid relay agent option, the option will be stripped from the packet before it is relayed to the client.
The DHCP relay agent option consists of two pieces of data, called sub-options. The first is the agent
circuit ID sub-option, and the second is the agent remote ID sub-option. When the DHCP relay agent
option is enabled on switches running ExtremeWare XOS, the value of these sub-options is set as
follows:
●
Agent circuit ID sub-option: Contains the ID of the port on which the original DHCP request packet
was received. This ID is encoded as ((slot_number * 1000) + port_number) . For example, if the DHCP
request were received on port 3:12, the agent circuit ID value would be 3012. On non-slot-based
switches, the agent circuit ID value is simply the port number.
●
Agent remote ID sub-option: Always contains the Ethernet MAC address of the relaying switch.
You can display the Ethernet MAC address of the switch by issuing the show switch command.
To enable the DHCP relay agent option, use the following command after configuring the DHCP/
BOOTP relay function:
configure bootprelay dhcp-agent information option
To disable the DHCP relay agent option, use the following command:
unconfigure bootprelay dhcp-agent information option
In some instances, a DHCP server may not properly handle a DHCP request packet containing a relay
agent option. To prevent DHCP reply packets with invalid or missing relay agent options from being
forwarded to the client, use the following command:
configure bootprelay dhcp-agent information check
To disable checking of DHCP replies, use this command:
unconfigure bootprelay dhcp-agent information check
A DHCP relay agent may receive a client DHCP packet that has been forwarded from another relay
agent. If this relayed packet already contains a relay agent option, then the switch will handle this
packet according to the configured DHCP relay agent option policy. The possible actions are to replace
the option information, to keep the information, or to drop packets containing option 82 information. To
configure this policy, use the following command:
configure bootprelay dhcp-agent information policy [drop | keep | replace]
The default relay policy is replace. To configure the policy to the default, use this command:
unconfigure bootprelay dhcp-agent information policy
For more general information about the DHCP relay agent information option, refer to RFC 3046.
Verifying the DHCP/BOOTP Relay Configuration
To verify the DHCP/BOOTP relay configuration, use the following command:
show bootprelay