4 different leafs - same nexthop for static route - floating SVI?

[Ovidiu-Madalin Roset]

Dear experts,

Please help me with this matter.

I have 4 leafs connecting to the same Router, let's call it R1.

On ACI I need to configure a L3Out with static routes only. On R1 I need to configure a default route towards the ACI and I'd need a single common next-hop. With vPC you can only use 2 leafs, but that's not an option, I need all 4 leafs connected and I don't care about LACP :).

Would the floating SVI be a solution here? I think I could use let's say .5 as Floating IP and .1 to .4 on the 4 leafs and on R1 just use .5 as the next-hop for my default route?

What I'm also curious about is the Domains. I need a L3 Domain for the L3Out and a Physical Domain for the "internal BD" for the SVI flooding. Can I assign the same VLAN for these or I should create a different Physical Domain with a dummy VLAN (this won't be used ouside the fabric as I understand).

[disales · Accepted solution]

Hello there @Ovidiu-Madalin Roset 

Yes, floating SVI L3out would fit your requirements. And you could use the .5 as Floating IP and .1 to .4 on the 4 leafs and on R1 just use .5 as the next-hop as you mentioned.

As for the domain you could map the floating SVI (vlan from you l3domain) to the phys domain, have a look at the "Configuring Multiple Encapsulation for L3Outs With SVI and Floating SVIs using the GUI" section of the configuration guide for your version of aci (here is the doc for the whitepaper on floating SVI) where you can have a look at the same section to get an idea of what it means.

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/kb/Cisco-ACI-Floating-L3Out.html#Cisco_Concept.dita_f6ea6a77-657e-46bf-b5b3-2065b5a3ffdc

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[STEPAN JANKOVIC]

Hello,

Floating L3out is a bit tricky...

Floating IP address shouldn't be used for routing. Create secondary ip address, the same IP on all leafs, and use this one as a next hop on external router. This is described in https://www.cisco.com/c/en/us/td/docs/dcn/aci/apic/all/floating-l3outs/simplify-outside-network-connections-using-floating-l3outs.pdf

Please also note, that static route on ACI side will be propagated regardless the next hop (external router) is accessible or not. This weird behavior can be corrected using IP SLA tracking of external router reachability on every leaf.

Stepan