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ARP problems with new 2950

As the first stage or our network upgrade I've installed a new 2950, to work as the core switch in our network. Since then we've had an increasing number of PCs (starting with 2, rising to 20 over a week) who are suffering from ARP problems.

If you ping (or use an app) from an erring PC its will fail to obtain the MAC address, it will usually resolve it after several ping attempts. When the ARP entry expires the problem occurs next time. Manually entering the ARP entry on the PC solves the problem.

I've checked all switches and they have the correct entries in their MAC tables.

Any idea why we would suddenly have ARP problems? This is definately linked to the installation of this new switch.

Our topology is:

Catalyst 2950G-48-EI at the core.

All other switches and servers connect into the core.

The other switches are a mixture of 3Com SuperStack I, II and III. Eiight in total.

All users connect into the 3Com switches.

The 2950's details are:


IOS 12.1(11)EA1, C2950-I6Q4L2-M.



  • Other Network Infrastructure Subjects

Re: ARP problems with new 2950

Working with 3Com in the past I recall a Network Port/ Uplink port configuration on the superstack line of switches. This would be the port where the 3Com would not learn MACs and flood traffic (towards the core/router).

Assuming this is all correct there is a defect that might be getting you here as well. CSCdz00216 (duped to CSCdz13373) defines an intermittent arp issue with dynamic vlan ports. It is fixed in 12.1(13)EA1& 12.1(12c)EA01.

Hope this helps you,


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