how to debug arp ?

[LaurentH]

Hello,

 i am getting an unresolved issue on some procurve switches on my LAN (one 2810 and two 4200vl cascaded):

(HP 4100)-----(L3 Juniper EX switch)----------(HP 2810)-----(HP 4200)-------(HP4200)------(Workstations)

On a specific VLAN, mac address cache of all workstations continiously change. The symptoms are similar of some loop on this vlan upward except no loop are detected anywhere (l10 workstations on the vlan) :

Everything works well and suddenly on every of the right 3 Procurve switches 'show mac-address vlan XXX' tell me the Workstation's MAC address are on the L3 switch side.

On the L3 switch and HP 4100 side, the arp cache doesn't move and points the workstations well too the 3 HP side (which make me think this is not really a loop issue).

I think, for an unknown reason, some arp annoucement comes from the L3 switch side updating the 3 HP mac address cache for this vlan periodically.

Theses switches support other vlans where everything is well

I don't find any command on the HP switches to debug arp requests or troubleshoot anything. Does anyone know how i can see if arp/garp traffic come to the uplink of the HP switches ?

thank you and sorry for my bad english.

[Vince-Whirlwind]

I saw the same kind of behaviour once on a Nortel network (4550 switches, from memory).

It was fixed by a firmware upgrade.

Does the Juniper switch have an aggregated link to the 2810?

[LaurentH]

Hello,

    No lacp between these two switches (fiber link)