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New Member

Are Servers updated when a Gateway MAC address changes?

We have a server connected to a 3560 switch which in turn connects to 6500s. The gateway interface is on the 6500. We will be changing the 6500s so the mac address for the gateway will change, however the IP address will remain the same. As we change out the 6500s the uplink connections to the 3560 will go down. This will flush the old mac address from the 3560.

When the 3560 removes a MAC address does it update servers so they have to relearn the correct MAC address?

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Accepted Solutions
Hall of Fame Super Silver

Are Servers updated when a Gateway MAC address changes?

I would not expect the 3560 to update the servers when it relearns the MAC address. I would expect the server would need to relearn the MAC address on its own. The good news is that most servers have fairly short ARP timers, so the situation would straighten out as host ARP timers expire and the host ARPs for the address and learns the new MAC. If you have some servers that have longer timers or if you are concerned about having quick and complete convergence then you may need to do something to clear the cache for ARP on the servers.

HTH

Rick

Cisco Employee

Are Servers updated when a Gateway MAC address changes?

Hello,

In addition to Rick's perfect reply, you can force your 6500 to send a gratuitous ARP response using the command clear arp or more selectively, clear arp interface X where X is the name of the gateway interface. That should cause each device update its ARP cache.

Best regards,

Peter

4 REPLIES
Hall of Fame Super Silver

Are Servers updated when a Gateway MAC address changes?

I would not expect the 3560 to update the servers when it relearns the MAC address. I would expect the server would need to relearn the MAC address on its own. The good news is that most servers have fairly short ARP timers, so the situation would straighten out as host ARP timers expire and the host ARPs for the address and learns the new MAC. If you have some servers that have longer timers or if you are concerned about having quick and complete convergence then you may need to do something to clear the cache for ARP on the servers.

HTH

Rick

Cisco Employee

Are Servers updated when a Gateway MAC address changes?

Hello,

In addition to Rick's perfect reply, you can force your 6500 to send a gratuitous ARP response using the command clear arp or more selectively, clear arp interface X where X is the name of the gateway interface. That should cause each device update its ARP cache.

Best regards,

Peter

New Member

Are Servers updated when a Gateway MAC address changes?

Great!  Thanks. Now I have another trick.

New Member

Are Servers updated when a Gateway MAC address changes?


Thanks!  Great explanation

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