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How can I debug ARP traffic in a Catalyst 6509

The ARP requests are apparently not being forwarded by the switch. At the end of two Ethernet port-channel links there are two systems belonging to the same VLAN. The ARP request from A to B is OK, but from B to A is not. Tracing on the end systems show that A is not receiving the request that B sends. So we need to know what is doing the switch with these frames.

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Re: How can I debug ARP traffic in a Catalyst 6509

Can you sniff the port going to A using the span function ? Make sure you span the port connected to B as well. ARP request is a broadcast packet and hence it should be sent on all ports on that vlan. If it is not working, it is possible that it could be a bug.

You can try L2 trace command

You may want to make sure you are running latest software on the switch and open a TAC case if you need further assistance.

Community Member

Re: How can I debug ARP traffic in a Catalyst 6509

We are having a similar problem. We have a 6509 but aren't running CatOS. We are running IOS rev 12.1(8b)E8. The system that is apparently not receiving the ARP request is an HP9000 running HP-UX 11i (11.11) and we are port-channeling to it across 1000base-SX connections. The 9000 has two partitions in this configuration and both are exhibiting the same behavior. There is a third partition not running port-channeling that is working fine. No other hosts on this VLAN have this problem. All hosts (NT, 2000, Linux, AIX, OS/400) on that VLAN have problems getting ARP requests to the two partitions on the HP9000. The HP9000 itself has no trouble initiating communications with any other hosts.

We have proven that the ARP requests are occurring and all other hosts can see them. Using the HP to do traces of its own interfaces, we cannot see the ARP requests. We have been unable, as of yet, to SPAN the port-channeled ports on the 6509 and see if the switch shows that it is trying to send them. Expecting a gigabit interface for our sniffer today and hope to have a capture by day's end.

Any help anyone can provide will be much appreciated.


Tyler West

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