If there is a layer 3 device connected to another layer 3 device & if there is a physical unit change made on one of them..shouldnt the mac-address clear itself after the aging period & reflect the new device physical address.Do we really need to clear the mac manually from the other device.Just part of a replacement coming up next weeek, so just making sure every problem area is checked upon.
if am correct the arp timeout is 360seconds...so when the takeover to new layer3/layer2 info is being done...the static unchanged device would timeout the current entries for the old device & use the new ones?
how is gratuitous different from normal learning?
Any possible reasons that would have the unchanged device unable to relearn the new entries?
Gratuitous means that the ARP announcement was made by the new device without being requested in an ARP request, as is done in "normal learning." Hence, it is gratuitous.
Keep in mind that the gratuitous ARP will also be used by inter-connecting layer 2 switches to update their CAM tables. The switches will learn that to get to the failover MAC address, it will have to forward traffic out another port. Rememeber, the switch learns new MAC addresses as it receives traffic on its ports. So, when the new L3 device sends out the grat. ARP, the switch will "learn" that the source MAC address can now be learned from a new port.
"Any possible reasons that would have the unchanged device unable to relearn the new entries?"
Sometimes security appliances do not repsond well to grat. ARPs for fear that it is part of some sort of attack. In that case, the ARP cache will have to time out or you will have to manually clear it.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...