ACI Multi-Pod Building Control Plane
IS-IS infrastructure protocol is used to build the IS-IS adjacency between Spine and Leaf in ACI fabric, it also exchanges IP information of each VTEP which is assigned (Locally defined loopback address from TEP pool) during auto-Provisioning process.
In Multi-Pod deployment each pod is assigned a separate TEP non overlapping POOL of IP address as shown in below figure:
Each POD Spines are OSPF Peers with directly connected Spines which further exchanges the POD TEP pool and Host specific information between each other. At spines these routes learned via OSPF gets redistributed to IS-IS which helps Leaf in each Pod to install those routes in their routing table.
Below figure show the options of routing protocol can be used