HSRP Behavior
Issue:
I have 2 Cisco 3560 Switch connected and a Trunk link is configured between them allowing all the VLAN. Also HSRP is configured with virtual IP address as 192.168.1.100. A server is connected with Teaming/Multipath configured in its NIC. SWITCH 1 is ACTIVE & SWITCH 2 is STANDBY.
By Chance if the trunk link between the switches goes down both the switches will become ACTIVE.
In this scenario, how the traffic flow path is going to be? Since the virtual IP MAC will be given by both the switch, which path the Server NIC will choose?
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Resolution:
If only one NIC is active then any traffic coming into the switch with the standby NIC connection destined for the server would need to be sent across the switch interconnect.
If the interconnect fails between the switches this does not affect the active server NIC. The active server NIC will stay the same and therefore the server will continue to use the switch it was using before the failure. Obviously though return traffic may very well not reach the server as it may come in on the other switch.
Best practice is always to run more than one physical link between 2 switches doing HSRP, so you should definitely look to use Etherchannel for link redundancy.
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