Customer have one VMware server connected with 4 interfaces from gi2/0/33 to gi2/0/36 to our switch stack.
When customer shuts down main interface gi2/0/33 to test the failover, the ping from our switch or from end device to the server fails.
We have noticed, after checking traffic statistics and captured packets, that VMware server was not sending ARP request when the main interface was down so our switch was waiting for the time to expire before refreshing ARP table.
So because the switch had the MAC address on wrong port the ping fails. Only after the time expires and switch refresh ARP table the ping starts again.
VMware server was not sending ARP request when the main interface was down so our switch was not ale to upgrade the MAC table until the refresh time expires. The switch was using the old entry until arp refresh and only after that it was able to update the mac table
We configured the command mac-address update arp.
The mac-address update arp command enables the MAC address-triggered ARP entry update function.
The Switch is enabled to update outbound interfaces in ARP entries when outbound interfaces in MAC address entries change.
On the Ethernet, MAC address entries are used to guide Layer 2 data forwarding.
The ARP entries that define the mapping between IP addresses and MAC addresses guide communication between devices on different network segments.
The outbound interface in a MAC address entry is updated by packets, whereas the outbound interface in an ARP entry is updated after the aging time is reached.
In this case, the outbound interfaces in the MAC address entry and ARP entry may be different.
To address this issue, run the mac-address update arp command to enable the Switch to update outbound interfaces in ARP entries when outbound interfaces in MAC
address entries change.
Customer tested and everything was fine – the failover was working and issue solved.
We recommend to use EtherTrunk interface for this scenario, so the server will use all the interface and also do load balance. In case the customer does not want this you should use mac-address update arp command.