Azure Virtual Network Gateway learned routes

Question

Azure Virtual Network Gateway learned routes

Peter Stieber 180

On VirtualNetworkGateway (type VPN) I am learning the prefix from 2 sources - from another VPN gateway (eBGP) and from VirtualNetworkGateway - type ExpressRoute (iBGP). Transit between both gateways is enabled. Which route is preferred ?

    [
      {
        localAddress: '10.3.160.79',
        network: '10.3.4.0/24',
        nextHop: '10.3.5.62',
        sourcePeer: '10.3.5.62',
        origin: 'EBgp',
        asPath: '64550-64540',
        weight: 32768,
      },
      {
        localAddress: '10.3.160.79',
        network: '10.3.4.0/24',
        nextHop: '10.3.160.78',
        sourcePeer: '10.3.160.133',
        origin: 'IBgp',
        asPath: '64550-64540',
        weight: 32768,
      }]

Jeevan Shanigarapu 5 Reputation points Microsoft External Staff Moderator

2025-08-12T14:59:59.2566667+00:00
Hello @Peter Stieber,

Hope you are doing well.

Thanks for reaching out to Microsoft Q&A.

In your configuration, the Virtual Network Gateway (VPN type) receives the same prefix from two sources:

Another VPN Gateway through eBGP

A Virtual Network Gateway (ExpressRoute type) using iBGP with transit enabled

Azure selects the preferred route based on its BGP process. By default, ExpressRoute (iBGP) routes have a higher local preference, so Azure typically chooses the ExpressRoute route for that prefix. This is because ExpressRoute provides a private, dedicated connection with higher reliability and performance.
In your case, Azure chooses the ExpressRoute path because iBGP routes from ExpressRoute are assigned a higher local preference value than routes learned from the VPN Gateway.

To change the route, you need to adjust the BGP settings such as local preference, AS path prepending, or MED values, as these can alter the routing behavior. If you don’t apply any custom settings, the traffic will generally use the ExpressRoute path.

If you want to prefer the VPN Gateway route, you can modify BGP attributes, such as lowering the local preference for ExpressRoute or using AS path prepending.

You can verify the active route by checking the BGP routing table on the Virtual Network Gateway or using Azure diagnostics.

Get-AzExpressRouteCircuitRouteTableSummary (Az.Network) | Microsoft Learn

Detailed explanation on BGP route selection process in Azure:

BGP (Border Gateway Protocol) uses several attributes to determine the best path when multiple routes to the same prefix exist. Key attributes include: Weight, Local Preference, AS Path Length, Origin Type, MED and eBGP over iBGP.

Weight – This is a Cisco-specific attribute that is not shared with other routers. Routers will prefer paths with a higher weight value. Local Preference: Routes with higher local preference values are preferred, by default the value is 100.

AS Path: Routes with shorter AS paths are generally preferred. You can use AS path prepending to increase the path length and make a route less desirable.

Origin Type – It always preferred the IGP instead of EGP

MED (Multi-Exit Discriminator): Suggests preferred entry point into an AS, It preferred the lowest value.

EBGP over IBGP: If all other factors are the same, routes received through eBGP are chosen over those learned via iBGP.
Supporting document:
About BGP with VPN Gateway - Azure VPN Gateway | Microsoft Learn

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

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