question of arp when vpc with hsrp

[szeyukit1]

i am just studying the vpc by myself.

but i am confused about the arp

for example,

n7k-sw1 and N7K-sw2 is configured as VPC domain, using port channel connect to downstream switch may be a 3750 named as sw3

if sw1 and sw 2 also form a hsrp group 1, and sw1 is active which i read from study unit that only hsrp active member will answer ARP request.

if hsrp virtual ip is the gateway of sw3, sw3 send ARP request through the port channel and hash to sw2 which is hsrp stanby member.

and sw2 will send the packet to sw1 through peer link as it is active member, but for the loop avoidance rule, it can't send back to sw3 through the member port?

so how does arp work operational? 

many thanks everyone

[Masoud Pourshabanian · Accepted solution]

Hello,

ARP is handled by control plane and VPC loop-prevention is implemented by data plane.

In nexus with VPC, active hsrp replies the ARP packets but both active/standby forward traffic in data plane.

If hsrp standby receives an ARP request, it forwards it to active hsrp through peer-link. Then, active hsrp, replies back directly to the requester since it sees requester mac address on one of its port. 

If instead of ARP request, traffic passes peer-link, nexus does not forward it to its member ports because of loop prevention in data plane(Orphan ports are exemption).

Masoud