Following are the failure scenarios we are going to discuss below:
1) vPC Keep-Alive Link is Down
--> Nothing happens if the Keep-Alive link goes down between the vPC members.
--> No impact on the Data Traffic.
--> Virtual Port-Channel is still in UP state in both vPC Primary/Secondary Members
--> Interface SVI VLAN's are UP in both vPC Primary and Secondary Members.
--> vPC Primary/Secondary roles will be retained on the vPC members.
--> There is only one issue that happens only when the vPC primary/Secondary also goes down after the Keep-Alive link stopped working. The vPC Primary/Secondary member cannot establish vPC once they come back online if Keep-Alive Link is Down.
--> Resolution: Troubleshoot the Layer 3 Connectivity to fix the issue of Keep-Alive Link between vPC Members.
2) vPC Peer Link is Down
--> All of the vPC Member ports of the Secondary vPC Member will be shut down if the Keep-Alive Link is up.
--> Impact on the Data Traffic.
--> Virtual Port-Channel is in UP state
--> vPC Primary only would be to continue to forward the traffic from member ports.
--> Interface SVI VLAN's are UP only in vPC Primary and Down in vPC Secondary.
--> Single attached devices connected to vPC Secondary member gonna lose network connectivity as all the SVI's related to vPC VLAN will be shutdown.
--> Single attached devices connected to vPC Primary member not gonna lose network connectivity as all the SVI's related to vPC VLAN are in UP State.
--> Resolution: Troubleshoot the Layer 2 Connectivity to fix the issue of Peer Link between vPC Members.
3) vPC Keep-Alive Link is Down and Peer Link Down after some time
--> If the vPC Keep-Alive Link is down and after some time Peer Link also goes down then both of vPC members gonna act as vPC Primary.
--> Impact on the Data Traffic.
--> Virtual Port-Channel is still in UP state in both vPC Primary/Secondary Members.
--> Interface SVI VLAN's are UP in both vPC Primary and Secondary Members.
--> This situation leads to a split-brain scenario as both of the vPC members are acting as Primary.
--> Resolution: Troubleshoot the Layer 2/3 Connectivity to fix the issue of Peer Link and Keep-Alive between vPC Members as well shut down one of the vPC Members.
4) vPC Peer Link is Down and Keep-Alive Link is Down after some time
--> If the vPC Peer Link is down and after some time Keep-Alive Link also goes down then the following things happen on the vPC Secondary:
i) vPC Member Ports/Interface VLAN's on the Secondary goes into shutdown state after Peer Link is Down
ii) vPC Secondary goes into the suspend state if the Keep-Alive Link goes down and does not go into up state unless the Keep-Alive Link comes up then the Peer Link also comes up.
Reference: Cisco.com,
Md.Kareemodddin,
CCIE #54579
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