Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 796)

766 Multi-Service IronWare Switching Configuration Guide
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DHCP option 82 insertion
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The Brocade device inserts DHCP option 82 when relaying DHCP request packets to DHCP servers.
When DHCP server reply packets are forwarded back to DHCP clients, and sub-option 2 matches
the local port MAC address, then DHCP option 82 is deleted. The vlan/port information is used to
forward the DHCP reply. Refer to the following figures:
FIGURE 196 DHCP option 82 is added to the packet
FIGURE 197 DHCP option 82 is removed from the packet
The option 82 insertion/deletion feature is available only when DHCP snooping is enabled for the
client/server ports, and when the device is configured as a DHCP relay agent. By default, DHCP
option 82 is off.
DHCP option 82 contains two sub-options; sub-option 1 (circuit ID) and sub-option 2 (remote ID).
Sub-option 1, relay agent circuit ID is in the following format.
VLAN id (2 bytes) / module id (1 byte) / port id (1 byte) (The module and port id will be 1
based).
The circuit ID identifies the location of the port, showing where the DHCP request comes from.
Typical address allocation is based on the gateway address of the relay agent.
Sub-option 2, Remote ID is in the following format.
Brocade NetIron XMR base MAC address (6 bytes)