Traffic load balancing using Active-Active express route circuit with different peering location

Question

Hi,

I want to load balance traffic using active - active express route circuit with different peering locations. I gone through Microsoft document and it is mentioned that only active - passive load balancing is possible. I have following scenario.

On premise locations are connected to cloud provider using MPLS. There are 2 locations. Azure Location A (primary) and Azure location B (DR). Azure location A is connected to local express route circuit (exp ckt A - peering location X) and Azure Location B is connected to local express route circuit (exp ckt B - peering location Y). Both express route circuits are configured with different peering location

Now I want to create express route connection from Azure region A to exp ckt B and Azure region B to exp ckt A. So I will have two express route connection for both Azure region with on premise.

My requirement is I want to utilize both express route circuit if on premise connect with Azure region A and Azure region B

on-premise -> exp ckt A+ exp ckt B -> Azure region A
on-premise -> exp ckt A+ exp ckt B -> Azure region B

As per Microsoft, I can configure active - passive with multiple express route circuit but I want to use active - active with multiple express route circuit.

Please suggest whether it's possible to achieve this and also whether this exp circuit can be part of same subscription or different subscription.

Answer 1

Hello @Siddhesh Rane ,

I understand that you would like know if it is possible to load balance traffic using Active-Active express route circuits with different peering locations.

The configuration is described in the below article (you just need to make a few changes from the advised steps):
https://learn.microsoft.com/en-us/azure/expressroute/designing-for-disaster-recovery-with-expressroute-privatepeering#large-distributed-enterprise-network

In order to achieve your requirement, you have to remove a few configurations as below:
If you do not set AS path prepending in BGP peering and do not set Weight in the Connection, the IP routing metric for the two ExpressRoute circuits will be the same and the traffic from Azure region to on-premises will pass in balancing through both Connections.
i.e. from a vnet in the Azure region A, the packets will take the Connection to the ER ckt A or the Connection to the ER ckt B.

To answer your below question,

Please let me know whether its possible to have active active traffic flow. It would be great if I get to know what could be disadvantages between active - active with active - passive.

Yes, it is possible to have active-active traffic flow if you do not influence the routing by setting AS path prepending or weight in your ExpressRoute connections..
However, if the two ExpressRoute locations, where the ER ckt A and ER ckt B are deployed have high relative distance, then you might have different end-to-end delay in balancing traffic through the different connections. This is an aspect which should be evaluated. A deterministic path avoids difference in latency.
The disadvantage is you would experience inconsistent network performance and increased latency end-to-end.

Kindly let us know if the above helps or you need further assistance on this issue.

----------------------------------------------------------------------------------------------------------------

Please "Accept the answer" if the information helped you. This will help us and others in the community as well.