topic Re: Stretching BD and its subnet in Multi-Site in Application Centric Infrastructure

Stretching BD and its subnet in Multi-Site

SandevChopra07800 — Mon, 16 May 2022 15:29:30 GMT

Hi, I have a question on stretching the BD and its subnet via the NDO/MSO. Lets say we stretch the BD and its subnet with the l2stretch flag enabled, then if there is a vm-mobility event in the background and a vm moves over to the 2nd site. Where does the vm`s default-gateway reside? Still the primary site OR it is on both the sites now depending on where the endpoint is located?

Also, is there a separate option to enable host-based route in the BD or that's by default when we stretch? Where is that found?

Much thanks!

Re: Stretching BD and its subnet in Multi-Site

Sergiu.Daniluk — Mon, 16 May 2022 16:58:42 GMT

Hi @SandevChopra07800

When you stretch a BD and it's subnet configuration, automatically the subnet will be configured in both sites, on all leafs where you have the endpoints connected.

The host base routes is enabled under the BD config:

+ locally to APIC, if you want to enable for BDs non-imported in MSO/NDO:

+ or in MSO/NDO if your BD is already imported in it:

Stay safe,

Sergiu

Re: Stretching BD and its subnet in Multi-Site

SandevChopra07800 — Mon, 16 May 2022 17:43:15 GMT

Thanks a ton Sergiu !

Will the host-based route be advertised over an ospf-based L3out in the VRF? { We are not doing GOLF which uses MP-BGP as it does not qualify in the specific customer deployment }.

Re: Stretching BD and its subnet in Multi-Site

Sergiu.Daniluk — Tue, 17 May 2022 05:19:11 GMT

Yes, by enabling "advertise host routes", the Border Leafs will advertise host routes (/32 or /128 prefixes) out through the L3Out's dynamic routing protocol, regardless which one it is configured. This works with Gen2 or newer switches (-EX, -FX -FX2/3 etc).

For more details about host routes advertisement, I encourage you to read the config guide:

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/4-x/L3-configuration/Cisco-APIC-Layer-3-Networking-Configuration-Guide-401/Cisco-APIC-Layer-3-Networking-Configuration-Guide-401_chapter_011.html

Stay safe,

Sergiu