Arp problems with Port Channel / Trunk

Unanswered Question
Sep 27th, 2007

Hi,

We have two cat 5509's connected with a port channel. SwitchA can't see MAC addresses on SwitchB and visa versa.

I'm going to try to post as many info as possible, hope it is all readable

This is the setup:

cat os 5.5 on both switches

Port channel and trunk on switchA:

Port Status Channel Admin Ch

Mode Group Id

----- ---------- -------------------- ----- -----

2/1 connected on 159 801

2/2 connected on 159 801

----- ---------- -------------------- ----- -----

Port Device-ID Port-ID Platform

----- ------------------------------- ------------------------- ----------------

2/1 067532363(cat5509.B 2/1 WS-C5509

2/2 067532363(cat5509.B 2/2 WS-C5509

----- ------------------------------- ------------------------- ----------------

Port Mode Encapsulation Status Native vlan

-------- ----------- ------------- ------------ -----------

2/1 on isl trunking 1

2/2 on isl trunking 1

Port Vlans allowed on trunk

-------- ---------------------------------------------------------------------

2/1 2,500,900

2/2 2,500,900

Total Matching CAM Entries Displayed = 171

Port channel and trunk on switchB:

Port Status Channel Admin Ch

Mode Group Id

----- ---------- -------------------- ----- -----

2/1 connected on 160 801

2/2 connected on 160 801

----- ---------- -------------------- ----- -----

Port Device-ID Port-ID Platform

----- ------------------------------- ------------------------- ----------------

2/1 067528845(cat5509.A 2/1 WS-C5509

2/2 067528845(cat5509.A 2/2 WS-C5509

----- ------------------------------- ------------------------- ----------------

Port Mode Encapsulation Status Native vlan

-------- ----------- ------------- ------------ -----------

2/1 on isl trunking 1

2/2 on isl trunking 1

Total Matching CAM Entries Displayed = 93

When I try to match mac addresses I get:

switchB> sh cam 00-30-48-83-62-80

doesn't match any port but on switchA it does:

switchA>sh cam 00-30-48-83-62-80

2 00-30-48-83-62-80 3/17 [ALL]

Total Matching CAM Entries Displayed = 1

This a 'simple' server directly connected to port 3/17. Netmask 255.255.255.0

To make it 'more interesting', not all servers have this problem but I can't find any common thing on the server which I can isolate.

The trunk has three vlans, all servers I'm talking about are in vlan 2 and the trunk has this vlan

I 'suspect' the port channel between the switches but why should it 'block' arp messages.....

The traffic intended for the servers on switch A which arrives first on switchB (because of the network setup) now gets broadcasted over switchB, ends up at switchA via the port channel and reach the destination. But this is not the way it should go.

Hope someone has an idea / can help.

Kind regards and thanks in advance

Jappe

I have this problem too.
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