Dhcp relay agent option 82 – Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) User Manual
Page 1426
DHCP Snooping Introduction and Configuration
Software Reference for x310 Series Switches
55.4
AlliedWare Plus
TM
Operating System - Version 5.4.4C
C613-50046-01 REV A
DHCP Relay Agent Option 82
If the switch is at the edge of the network, it can be configured to insert DHCP Relay Agent
Option 82 information into client-originated BOOTP/DHCP packets that it is forwarding to
a DHCP server. The switch also removes DHCP Relay Agent Option 82 information from
BOOTP reply packets destined for an untrusted port if the DHCP client hardware is directly
attached to a port on the switch.
DHCP servers that are configured to recognize DHCP Relay Agent Option 82 may use the
information to implement IP address or other parameter assignment policies, based on
the network location of the client device.
When DHCP Relay Agent Option 82 information for DHCP snooping is enabled, the switch
inserts DHCP Relay Agent Option 82 information into BOOTP request packets received
from an untrusted port. The switch inserts the following DHCP Relay Agent Option 82
information:
■
Remote ID: this identifies the host. By default, this is the MAC address of the switch
(sub-option1).
■
Circuit ID: this specifies the switch port and VLAN ID that the client-originated DHCP
packet was received on (sub-option2). By default, this is the VLAN ID and the Ifindex
(interface number).
■
Subscriber ID (optional): this is a string of up to 50 characters that differentiates or
groups client ports on the switch (sub-option 6).
Support on this
switch
This switch inserts DHCP Relay Agent Option 82 (agent option) information into DHCP
packets received through untrusted ports, and removes it from DHCP packets transmitted
through untrusted ports. This is enabled by default, and can be disabled if required.
You can specify values for the Remote ID and Circuit ID sub-options of the DHCP Relay
Agent Option 82 field. The Remote ID can be specified as an alphanumeric (ASCII) string, 1
to 63 characters in length. The Circuit ID can be specified as the VLAN ID and port number.
Subscriber IDs can be configured for ports, and if they have been configured, they are
inserted in DHCP packets as part of the DHCP Relay Agent Option 82 information.
Regardless of whether DHCP Relay Agent Option 82 is enabled for DHCP snooping, if the
switch receives a BOOTP/DHCP request packet on a trusted port, and the packet contains
DHCP Relay Agent Option 82 information, it does not update the DHCP Relay Agent
Option 82 information for the receiver port. By default, if it receives a DHCP request packet
containing DHCP Relay Agent Option 82 information on an untrusted port, it drops the
packet. However, if the switch is connected via untrusted ports to edge switches that
insert DHCP Relay Agent Option 82 information into DHCP packets, you may need to allow
these DHCP packets through the untrusted ports—the switch can be configured to
forward these packets.
Note that the DHCP Relay Agent Option 82 agent information inserted by the DHCP
snooping differs from the information added by DHCP Relay (see
). The switch cannot be configured to use both the DHCP
relay agent option and DHCP snooping.