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vPC+, aka L3 on back-to-back vPC domains


Please consider this scenario, where L2 VLANS are spanning 2 data centers and where R1-R4 are L2/L3 N7K routers (replacing existing 6K).

(I wish VSS would be available also in N7K to make life 10x easier!!).

                      R1                  |                     R2

                       ||                    |                     ||

vPC peer-link  ||    =======MAN=======   ||  vPC peer-link

                       ||                    |                     ||

                      R3                  |                    R4

                               Site A         Site B

Attached to R1 and R3 there are (dual-attached via 6K access switches) servers that may need to communicate to other servers in the same VLAN on the other side of the MAN. Over the MAN the VLANs are trunked, so its fine. This traffic can go over R1 or R3 both for L2 (vPC) and for L3 (HSRP vPC enhancements).

Anway, there is also a global OSPF domain for inter-VLANs communication and for going outside the DCs via other routers attached to the above cloud.

I've heard there is a kind of enhancement request (or bug?, CSCtc71813) to have this kind of back-to-back vPC scenario to handle transparently L3 data (peer-gateway command should deliver also control-plane L3-info??). There are 2 workarounds available for this design:

1.       Define an additional router-in-a-stick using an extra VDC on each 7k. In this case, for example for R1 we would use 3 VDCs: 1 VDC for admin, 1 VDC for L2, 1 VDC for R1.

2.       Define static routes to tell each 7k how to reach the other 7k L3 next-hops.

a) What is the best workaround to choose in order to smooth the upgrade later to the version of vPC that will handles this issue?

b) Are there any more caveats I dont see? I havent seeen any link in CCO, so I am unsure how to proceed the design.

c) I would be tempted to think that using additional static routes is a better choice because it would easier to remove them once vPC+ is there.

What static routes shall I add? R1 to R2, R1 to R4 and so on and so forth? I miss the details of this implementation.

d) How would vPC+ looks like once (when?) is there?

Thansk for your valuable input in advance.


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