Switch and device cold standby problem

[infosateng]

Hello

I have to 2 devices plugged into at 2950 switch in a cold standby setup, one is power up and the other not.  Both have the same IP Address.  When I switch off the powered on device and turn on the cold stahdby, I don't have connectivity to this device.  On the switch I don't see a mac address for this device, and if I wait a long time eventually I may get connectivity, but I usually reset the switch and then all is fine.

I'm trying work out if its the switch or my equipment that is causing the problem.

[andtoth · Accepted solution]

Hi,

Probably because the ARP entry for the old device is still present on the device from which you try to access the newly booted up box. Note that if you see the devices through a router, the router is storing the ARP entry for that subnet.

If the ARP entry still points to the old device's MAC address, packets will be sent to the old MAC and no one will reply to it. You can check this by using the "arp -a" command on Windows/Linux or "show arp" on a Cisco device and look for the MAC address to see who's the owner of it. Note that the 2950 switch might not contain an ARP entry if you are reaching the devices from a 3rd box connected to the switch.

To solve this problem, you can either delete the ARP entries on the end device or a long term solution would be to use a unique IP on each device.

Andras