Viewing Dhcp Helper Addresses; Dhcp Option 82 - HP 2920 Series Multicast And Routing Manual

Example 38 Displaying startup configuration with DHCP relay disabled
HP Switch# show config
Startup configuration:
; J9726A Configuration Editor; Created on release #xx.15.xx
hostname "HP Switch"
cdp run
module 1 type J9726A
ip default-gateway 18.30.240.1
snmp-server community "public" Unrestricted
vlan 1
name "DEFAULT_VLAN"
untagged A1
ip address 18.30.240.180 255.255.248.0
no untagged A2-A24
exit
no dhcp-relay
Non-Default DHCP Relay
1
setting

Viewing DHCP helper addresses

To display the list of currently configured IP Helper addresses for a specified VLAN on the switch,
enter the show ip helper-address vlan command.
Syntax:
show ip helper-address [vlan <vlan-id>]
Displays the IP helper addresses of DHCP servers configured for all static VLANS
in the switch or on a specified VLAN, regardless of whether the DHCP relay feature
is enabled. The vlan <vlan-id> parameter specifies a VLAN ID number.
The following command lists the currently configured IP Helper addresses for VLAN 1.
Example 39 Displaying IP helper addresses
HP Switch(config)# show ip helper-address vlan 1
IP Helper Addresses
IP Helper Address
-----------------
10.28.227.97
10.29.227.53

DHCP Option 82

Option 82 is called the relay agent information option and is inserted by the DHCP relay agent
when forwarding client-originated DHCP packets to a DHCP server. Servers recognizing the relay
agent information option may use the information to implement IP address or other parameter
assignment policies. The DHCP server echoes the option back verbatim to the relay agent in
server-to-client replies, and the relay agent strips the option before forwarding the reply to the
client.
The relay agent information option is organized as a single DHCP option that contains one or
more suboptions that convey information known by the relay agent. The initial suboptions are
defined for a relay agent that is co-located in a public circuit access unit. These include a circuit
ID for the incoming circuit and a remote ID that provides a trusted identifier for the remote high-speed
modem.
1
Configuring DHCP relay 65