Multi-Pod Connectivity via External L3

Multi-Pod Connectivity via External L3

L3out is used to provide external connectivity in ACI Multi-Pod fabric deployment. Below figure shows how three pods are inter connected each other.

While doing this type of connection it can cause Asymmetric inbound and outbound traffic flows. This is because same external prefix was injected inside the multi-pod from each L3-Out connection and endpoints deployed in a given Pod would always leverage the local L3Out connection to send traffic to external destinations. If endpoints belonging to the same BD are connected across all the Pods of the Multi-Pod fabric, inbound traffic may be received via any of the deployed L3Out connections.

To avoid this we should cluster the stateful network service deployed across PODs either in Active/Standby or Active/Active

It may be possible that not all Pods may have local connectivity to external network, In that case the endpoints connected to PODs which does not have local external connection will send the traffic to other remote pods which has external layer 3 connectivity .Here routing matric to reach Border leaf of remote Pod would be equal , which will load balance the outbound traffic across separate remote Pods.

This also cause creation of asymmetric traffic pattern.

A specific use case is the one where different Pods are deployed inside the same DC location. In this case, it is typical to use a centralized connection toward the external network domain. As shown in Figure the end result is that traffic from endpoints connected to all the Pods must be hair-pinned to the Pod externally connected (Pod 1 in the example below).