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ExpressRoute Gateway Routing

Ali El Husseiny 60 Reputation points
2025-07-31T12:42:59.57+00:00

Hello ,

I have expressroute connection between my AVS (network /22) and the ER gateway in the tranist and ibgp session between the ER gateway and route server .

My concern is when viewing the learned routes from the ER gateway it will show all AVS routes and since there is ibgp session with the route server then the same routes will be viewing there right?

Also when incoming traffic to AVS and we check the route table in the ER gateway or the route server where the next hop will be the ER gateway or MSEE routers?

Just curious about routes flow in this part if this can be clarified and thank you!

Azure ExpressRoute
Azure ExpressRoute
An Azure service that provides private connections between Azure datacenters and infrastructure, either on premises or in a colocation environment.
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  1. G Sree Vidya 4,005 Reputation points Microsoft External Staff Moderator
    2025-08-01T00:07:07.5166667+00:00

    Hi Ali El Husseiny

    Yes, you're correct The ExpressRoute Gateway will learn all AVS routes via the ExpressRoute connection. Since you have an iBGP session between the ER Gateway and the Azure Route Server, those AVS routes will also be propagated to the Route Server.

    The Route Server will then advertise those routes to any connected BGP peers (like NVAs or other gateways).

    The ER gateway learns routes from the on-premises network via BGP over the ExpressRoute circuit.

    The ER gateway exchanges routes with the Microsoft Enterprise Edge (MSEE) routers using eBGP for private peering. The AVS routes advertised to the MSEEs are propagated to the ER gateway, and you can view these routes using the Get-AzVirtualNetworkGatewayLearnedRoute Azure PowerShell command. These routes will include the AVS /22 network prefixes.

    Refer: https://learn.microsoft.com/en-us/cli/azure/network/express-route?view=azure-cli-latest#az-network-express-route-list-route-tables

    2.Incoming Traffic to AVS to Next Hop: This depends on where the traffic originates and where you're inspecting the route:

    From On-Premises to AVS:

    • Next Hop in Route Table:
    • In on-prem routers: next hop is MSEE
    • In ER Gateway: next hop is AVS internal IP
    • In Route Server: next hop is ER Gateway From Azure VNet Peers to AVS:
    • If the VNet is peered and routes are propagated via Route Server
    • Next hop will be ER Gateway, as it’s the bridge to AVS.

    Sharing similar thread which will be helpful for you https://learn.microsoft.com/en-us/answers/questions/1741721/routing-tables-on-express-router-and-virtual-netwo

    I hope this helps! If these answers your query, do click the "Upvote" of which might be beneficial to other community members reading this thread.

    If the above is unclear or you are unsure about something, please add a comment below.

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