Connecting Leaf Switches back to back between two APIC clusters

[gman3]

Hi

Customer has two separate ACI fabrics and requires a direct connection between them using Leaf switches over a 1 G circuit using routed sub-interfaces

Should this work or is an external switch required between the Leaf switches?

(I realize that directly connecting Leaf switches in the SAME APIC cluster is not supported/will not work but I don't know if this also applies to connectingLeaf switches that are in different clusters).

Thanks

[Sergiu.Daniluk]

Hi @gman3 

Connecting two leaf switches (or 4 in a double-sided vPC) from different fabrics (not configured in MultiSite) is perfectly fine as long as you keep in mind some things:

- if the connection is intended to extend a VLAN, then make sure you do not have another L2 connection between the fabrics (either through another direct connect or through some other switches) since this will create a L2 loop.

- if the connection is for an L3Out (as in your case) and you use OSPF or EIGRP AND you do transit routing (either from another L3Out or redistribute static routes), you will have to change the VRF Tag in one of the fabrics. Otherwise the exported routes from one fabric will not be imported in the second fabric because of the default loop prevention agains routes tagged with default tag 4294967295.

BUT, also you have to make sure you do not make any routing loops there so be careful about it.

- if you have MCP enabled, you will need to add a key to avoid one of the fabric considering the MCP from the second fabric as it's own.

This are things which comes to my mind at this moment. If anyone from the community or from cisco are aware of other guidelines or limitations, feel free to add.

Cheers,

Sergiu

[gman3]

Hi Sergiu

Thank you for sharing your expert knowledge. I'm not sure if I will get a chance to test this out

[Ali Aghababaei]

Hi gman3

Are fabrics completely separated or working in  Multi-Site setup?

[gman3]

Hi Ali

Multi-Site setup

[Sergiu.Daniluk]

HI @gman3 

So the two fabrics are already in connected and configured in Multi-Site?

That changes the perspective, simply by the fact that you do not need to interconnect the fabrics through L3Out since you can exchange routes through the multi-site.

Can you give more details of what you are trying to achieve?

Thanks,

Sergiu

[Slient_night]

Hello Sergiu,

We have a client that has two fabrics configures on MultiSite and doesn't want to have his replication traffic pas through the Spine and his edge routers between the two sites.

is it possible to connect the two leaf switches from each site between each other and limit the Vlan to those ports only and the replication hosts?

Thanks