Cam agingtime

[3gcasper]

We are experiencing connectivity issues when during our network server backup. Devices on the same vlan/switch as the server being backed up loose their connections. I found an article on Cisco's website which desribed a similar situation and recommends chaning the CAM agingtime to 14,400 seconds which would be equal to the ARP timer on the router the remote backup server connects through. Since the default CAM times entries out after 300 seconds, it appears that all ports in the vlan are getting flooded with the backup traffic until the router updates the switch with the MAC address again.

What adverse affects could upping the CAM timer this high cause? Obviously entries in the CAM can become stale, but what will go wrong if for instance a laptop user moves to a different building and the CAM still shows the mac address going through a different trunk. Is this self correcting condition or will this be a problem?

Any other pitfalls with doing so?

[t.baranski]

My understanding is that, typically, a given CAM entry's stale timer is reset every time a packet is seen sourced from the entry's associated port and MAC address. ARP works the same way and it makes sense: there's no reason to time out an entry in a table if you know it's still valid (which you do if you're seeing matching packets).

Your problem is more likely a simple bandwidth issue. What are the devices in question losing connections to? Devices on other switches? If so, the trunks between switches may be getting conjested during the backups.

[3gcasper]

The switches are trunked over a dual FE channel, we have a performance monitor which shows they are only peaking at about 12% on the trunk during the backup period. Devices on the same switch & vlan loose connectivity with eachother when the backup is running out through trunk the the router. The packets between devices on the same switch/vlan aren't traversing any trunk, they stay local within the switch.