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DHCP Snooping on 3com S4210 problem

 
skvedo
Occasional Contributor

DHCP Snooping on 3com S4210 problem

Hi,

I'm setting up dhcp snooping with IP source guard and DAI on some 3com S4210 switches.

I found problem with recording bindings in snooping database. In some cases I know that there is PC connected to interface, it use the DHCP, even switch say in debbuging that there are DHCP traffic, connection on PC works with assigned address but there's no record when I execute display dhcp-snooping command.

By making some experiments on table lab I found that if DHCP traffic goes within 2 access ports (both client and server are at same vlan, both connected to access ports) than it is recorded. If I connect DHCP to trunk interface, if DHCP is communicating at untagged vlan of that trunk the binding is recorded (same behavior if use client on access port with vlan 1 or client on port with access vlan X and set on trunk port trunk pvid vlan X). If DHCP traffic comes tagged throw trunk the binding is not recorded on switch. In all cases no matter how it is configured client receives correct address from DHCP and can communicate.

By Google i found that on Cisco products you need to enable dhcp-snooping for vlans but on 3com did'nt find anything similar in documentation or any similar command in switch command line.

Did anybody had these issues to and figured out where is problem?

Can't ask HP directly because our technical support warranty already pass and they won't talk to me (tried in different situation).

Thanks for answers.

Michal