Azure traffic routing if both vwan express route connection and traditional express route gateway connection coexists

Siddhesh Rane 61 Reputation points
2024-09-24T20:55:36.6366667+00:00

HI,

I have following scenario.

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Azure region 3 is having traditional hub and spoke connecting to on-premise and other azure regions through WAN network. This set up will migrate to azure vwan .

I want to understand

  1. Like express route gateway, azure vwan will also advertise on-premises/ azure regions routes to hub vnet
  2. If all routes will be advertised by both express route gateway and azure vwan, which path/route will firewall select to reach on-premises
  3. If I connect vwan in production environment, will it affect existing connection before I delete it during migration. Can we preconfigure vwan and connect to Hub vnet and not affecting the set up
  4. Is there any downtime required, at which step and how much duration required
  5. I checked migration steps for this on Microsoft site but want to know migration steps if anyone performed previously
Azure Virtual WAN
Azure Virtual WAN
An Azure virtual networking service that provides optimized and automated branch-to-branch connectivity.
229 questions
Azure VPN Gateway
Azure VPN Gateway
An Azure service that enables the connection of on-premises networks to Azure through site-to-site virtual private networks.
1,565 questions
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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Accepted answer
  1. KapilAnanth-MSFT 47,206 Reputation points Microsoft Employee
    2024-09-25T08:03:34.1+00:00

    @Siddhesh Rane ,

    Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.

    I am afraid your network diagram is misleading.

    From the diagram,

    • I take is the "WAN" is Azure vWAN and not your MPLS
    • In the vWAN, you have a vHub for Region3
    • It has both a VPN Gateway and an ExpressRoute Gateway
    • The Region3HubVNet has a ExR Gateway of it's own

    Please let me know if my understanding is incorrect.

    Observation :

    • I don't understand the Blue Line between "WAN" and the Region3HubVNet
      • What does it indicate?
    • I see you are trying to establish a connection between the vWANvHub and the Region3HubVNet
      • Please note that a VNET can use only one Gateway at a time
      • It can either use it's own or use the Gateway to which it is peered to, but not both
      • So in your case, since the Region3HubVNet already has a ExR Gateway, you will not be able to connect it to the vWANvHub in the first place
      • See : Spoke VNet should not have a virtual network gateway
    • So the entire question of "routes will be advertised by both express route gateway and azure vwan" is invalid.

    Now, to answer your queries,

    1 . A. If I connect vwan in production environment, will it affect existing connection before I delete it during migration.

    • Can you elaborate?
    • By connections, if you mean the ExpressRoute path - as mentioned earlier, you will not at all be able to peer the Hub to vWAN as long as the Hub has a ExR Gateway

    1 . B. Can we preconfigure vwan and connect to Hub vnet and not affecting the set up

    • Yes and this is expected.
    • Preconfigure the vWANvHub's ExR Gateway to connect to the ExR Circuit
    • Then delete the Gateway in the Hub VNET and connect it to the vWAN.

    2 . Is there any downtime required, at which step and how much duration required

    • Yes
    • For production workloads, please have a scheduled maintenance window
    • Anywhere around 4-5 hours should be fine.

    3 . I checked migration steps for this on Microsoft site but want to know migration steps if anyone performed previously

    • I mentioned the steps in 1 B
    • It's recommended to follow the steps in Official MS Documents
    • See : Migrate to Virtual WAN

    Please let us know if we can be of any further assistance here.

    Thanks,

    Kapil


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