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HP4000M and Cisco router problem

Micah Brandon
Occasional Visitor

HP4000M and Cisco router problem


I have a problem that's baffling me. We have an HP4000M that carries a moderate amount of traffic (around 10Mbps). There are only a handful of machines that are pushing this data and then there are several machines connected to the switch that hardly push anything at all.

I notice that these machines that are rarely touched will drop out of the ARP table in the switch. When this happens, any device that must use that machine's gateway (not on the same network) can no longer communicate with the machine.

We have Cisco 7000 series routers. The only way to reach these machines that have been removed from the switch's ARP table is to execute a "clear arp" on the gateway. Or sometimes it's possible to hop (telnet/ssh in or use Terminal Services depending on the OS...) from a machine on the same network that is unaffected to the "down" machine and then initiate some type of network traffic from the inside.

I have tried setting the MAC Age Interval higher, but the switch seems to ignore this. After a few minutes of non-activity on certain machines, they are dropped from the ARP table and can't be reached from outside their respective networks.

This might very well be a router issue. But I'm running no less than IOS 12.2 on our routers and I have firmware version C.09.16 on the switch.

Actually, I have two HP4000Ms, but I never see this particular problem on the other one because ALL the machines there are busy all the time.

Has anyone else experienced this problem?
Ron Kinner
Honored Contributor

Re: HP4000M and Cisco router problem

I have had a similar problem where there were two boxes with the same IP (or MAC). This confuses the switch quite a bit. Also had a problem where a static MAC had been added to a switch's port MAC table and then the device was moved to a different switch in the same network.

Also you might want to check to see if you have abc turned on. Turn it off if it's on and on if it's off. (See chapter 6-106 in
Management and Configuration Guide for the HP ProCurve Switches 1600M, 2424M, 4000M, and 8000M (September 1999)

available on:


also check the Bcast Limit on each port. IF this is set too low it could block out ARPs. Supposedly 0 means the feature is turned off but you never know. You might want to set it to 50% just to see if it makes a difference.

Finally, on the Cisco router you can set static arps so at least it doesn't forget.

conf t
arp A.B.C.D MAC arpa
wr me

where A.B.C.D is the IP address of the box you want to reach and MAC is its MAC. The dots just mean keep adding them until you have all of them. Default timeout on the Cisco is 4 hours.

I can't find any reference to static arps in the manual for the 4000 but you might try typing
arp ?
on the command line and see if it has an option. Might also be something under the port configuration or security. Also see if there is anyway to set static MACs in each port's MAC table.