Inserting Option 82 Suboption 2 (Circuit ID) into DHCP Packets

[ikhal3d]

Hi,

I have a Cisco Catalyst Switch C9200 that I'm using as a DHCP relay agent on VLAN 5. The DHCP server is on a different subnet (hence the reason to use DHCP relay).

VLAN 5 has an IP address with IP helper address configuration as you can see:

interface Vlan5
 ip address 10.0.0.254 255.255.255.0
 ip helper-address 10.10.10.254 
end

The global configuration are shown below:

ip dhcp relay information option
ip dhcp relay information trust-all

The switch will have clients booting up to perform zero touch provisioning (ZTP)or Nexus POAP function. So a proper DHCP implementation is necessary. One of the layer 2 interfaces assocciated with the VLAN has the following configuration:

interface GigabitEthernet0/0
 switchport access vlan 5
 switchport mode access
 ip dhcp relay information option subscriber-id newsub1234

I would like to insert the subscriber ID information into Option 82, however this will not work based on the Gig0/0 configuration shown above.

The subscriber ID information will ONLY be inserted if I configure the subscriber ID information at the VLAN 5 L3 interface. This, unfortunately, is useess since I cannot identify the source port/description of the DHCP request.

I would like to insert the circuit-Id information into the DHCP request based on the layer 2 interfrace.

Relying on the source MAC address of the client is something that I'm trying to avoid since this requires going to each client and grabbing their MAC address from the back of the unit.

Is there a way of doing it? Cisco guides don't show how the circuit-ID (suboption 2) information can be inserted into Option 82.

Thank you.

[Deepak Kumar]

Hello,

In virtual environment, it didn't worked for me as well. But in above configuration, I can't see DHCP Snooping commands. is it enabled?

I will try on physical device and will come back

Have you tried below link:

https://www.firewall.cx/cisco-technical-knowledgebase/cisco-switches/1218-dhcp-snooping-option-82-relay-agent-message-format-analysis.html

[MHM Cisco World]

ip dhcp relay information option subscriber-id newsub1234

above command must config under SVI not under L2 receive the Broadcast DHCP, SVI is relay no L2 port.