Why cann't vPC be used between ACI Spine switches and ISN switches?

[m1xed0s]

I got this question today from a customer who is looking for setup a ACI multi-site environment and the question is: Can the links between spine switches and ISN switches (NX-OS N9K) setup as vPC? I do not think so but I honest do not know why either...So hope someone could help clarify.

I guess the main reason for his question is the redundancy provided by the vPC... I stole part of the Figure 53 from the ACI multi-site white paper to make the topology below for reference...  

[Robert Burns · Accepted solution]

vPC is an L2 redundancy feature. L3 IP links offer improved redundancy and faster convergence than L2.  ACI Spine IPN connections  also must explicitly use sub interfaces (not SVIs) that would be required for for L3 VPCs.   The solution is tried and tested and not really lacking with anything that VPC would offer IMHO.

My 2cents.

Robert

[m1xed0s]

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@Robert Burns wrote:

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must explicitly use sub interfaces (not SVIs)

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Thanks I forgot about that VLAN 4 sub-interface requirement...