Cisco ACI - CDP and LLDP

Cisco ACI has the concept of Anycast Gateway where the default gateway of the subnet (configured with the Bridge domain) exists on the Leaf devices. Now, more importantly, the anycast gateway / SVI (Switched Virtual Interface) is configured (rather programmed) on only those Leaf switches which have endpoints belonging to that bridge domain.

How does Cisco ACI determine whether it should configure an SVI on a particular Leaf?

It does this via CDP, LLDP or OpFlex (if the endpoints support it).

This would imply, that CDP / LLDP is not just there for operational purposes, but rather, it actually holds a powerful influence on the actual traffic forwarding, unlike traditional switches.

CDP uses the usual Cisco CDP timers with an interval of 60s and a holdtime of 120s.
LLDP uses the usual LLDP timers with an interval of 30s and a holdtime of 120s.

CDP support for Fabric Extenders has started from ACI 2.2 release. For older releases, LLDP should do the trick.

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