Imagine that both the vPC peer keepalive link and vPC peer link have gone down. I am trying to understand how will that lead to unpredictable traffic flows or loops.
From what i have read on Cisco docs:
If the vPC keepalive link fails first and then a peer link fails, the vPC secondary switch assumes the primary switch role and keeps its vPC member ports up. If the peer link and keepalive link fails, there could be a chance that both vPC switches are healthy and the failure occurs because of a connectivity issue between the switches. In this situation, both vPC switches claim the primary switch role and keep the vPC member ports up. This situation is known as a split-brain scenario. Because the peer link is no longer available, the two vPC switches cannot synchronize the unicast MAC address and the IGMP group and therefore they cannot maintain the complete unicast and multicast forwarding table.
I understand the above, but i want to further dig deep into how loop might occur.How will unpredictable traffic scenario occur? I understand that there will be two vPC primary switch(both of them will act as STP root).Can you please clarify by using a simple topology?
On further searching, i see the below post here
From what i understood, since we have 2 switches acting as vPC Primary(and hence both of them will be STP root as well), the links will be in forwarding state and hence there are chances of loop. Is that correct understanding? I am also trying to figure out, if a packet is sourced from S1, how is that likely to undergo loop?