Failure modes include the following:
AARP infrastructure failure including shunts
For AARP to remove asymmetry, the AARP link must be synchronized between peers and all components of the shunts (Ipipe shunts and interface shunts) must be up and operational. If any of those components has failed, each AARP ID operates as standalone and diverts locally. Asymmetry is not removed.
failure of one of the interfaces to the dual homed site
Routing moves all traffic to the remaining link/node if this is the master AARP peer node no action is required. For any traffic the backup node, inter-chassis shunting is used. There is no change to the AARP master/backup state. Traffic is still processed by the same ISA as before the failure.
network reachability fails to master AARP node
AARP node loses reachability on the network side. This does not trigger an AARP activity switch, the shunt is used to move traffic from the backup node to the master node for the duration of the reachability issue. Routing should take care of traffic reconvergence. However, if the peer AARP is also not reachable, both nodes go on standalone mode and there is no asymmetry removal.
master AA ISA failure
AARP activity flips for all the master AARP instances linked to this local ISA if there is no local spare available. Any traffic arriving on the node with the failed ISA uses the shunt to reach the master ISA.