Problem with DHCP Snooping and Option 82 (Resolve)

nikita_kulikov — Tue, 07 May 2019 11:59:47 GMT

Hi team!
I test DHCP Snooping on switches ICX7250 and ICX7150 (hw ver. 8.0.9). DHCP-Server was Cisco switch.

I configured DHCP Snooping according to manual:
enable acl-per-port-per-vlan
ip dhcp snooping vlan 100
interface lag 1
dhcp snooping trust

Clients on untrusted ports didn't get ip addresses from DHCP-Server.
All because DHCP option 82 is enabled on ICX by default and switch addes it to requests. But Cisco switch doesn't understand this requests.

Debug log from ICX7250:
DHCP: snooping on for vlan 100, port 1/1/1
DHCP: rcv on port 1/1/1, intercept DHCP pkt, Request
DHCP: snooping on port 1/1/1, smac 10e7.c6e5.4d01, type 3, VRF default-vrf 0.0.0.0->10e7.c6e5.4d01
DHCP Option82: Adding option 82
DHCP Option82: 20 bytes added.
DHCP Option82: Adding option 82

Debug log from Cisco switch (DHCP-server):
DHCPD: Reload workspace interface Vlan100 tableid 0.
DHCPD: tableid for 172.16.0.1 on Vlan100 is 0
DHCPD: client's VPN is .
DHCPD: inconsistent relay information.
DHCPD: relay information option exists, but giaddr is zero.

I disabled DHCP option 82 and it's started work normally:
(config)#ip dhcp snooping relay information disable
or on interface
(config-if-e1000-1/1/1)#no ip dhcp snooping relay information

Maybe anybody knows another way to resolve this problem.

Re: Problem with DHCP Snooping and Option 82 (Resolve)

robert_placenci — Tue, 07 May 2019 15:50:56 GMT

option 82 is known to cause issues and it is recommended to disable it. Even on my 99% cisco network, the "no ip dhcp snooping information option" is a part of our standard configuration.

Re: Problem with DHCP Snooping and Option 82 (Resolve)

sushant_gaurav — Wed, 05 Feb 2020 19:25:01 GMT

Can you try ICX with ip helper-address configuration under a VE i.e. making it a relay agent and try inter-op with CISCO (DHCP Server)

By Default Cisco IOS devices reject packets with zero “giaddr” and by default Cisco Catalyst switches use “giaddr” of zero when configured for DHCP snooping

topic Re: Problem with DHCP Snooping and Option 82 (Resolve) in ICX Switches

Problem with DHCP Snooping and Option 82 (Resolve)

Re: Problem with DHCP Snooping and Option 82 (Resolve)

Re: Problem with DHCP Snooping and Option 82 (Resolve)