How to tweak the BGP Table of an Azure EXpressroute for one external IP address?

Diederik Janson 21 Reputation points
2022-04-29T09:55:05.61+00:00

Hi,

Several vnets we have in Azure are routed through our Expressroute back to our internal network. This works great.

For one vnet (Our Azure Virtual Desktop vnet) we made a udr (route table) of 0.0.0.0/0 with next hop internet.

Now I would like one external ip address not to go via the internet next hop but via the expressroute back to our internal network and then via our own external ip to the internet (this because of ip white listing on the destination). Because the traffice needs to go to an Expressroute circuit this needs to be done with bgp.

I have no idea how, can't find it in the documentation and i don't know if this is possible at all?

Any ideas?

Best Regards.

DJITS

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. Ahmed Muhi 1 Reputation point MVP
    2022-05-02T03:39:19.07+00:00

    Hey DJITS,

    So my understanding of your setup is this:

    1- You have a VNet that is the Azure Virtual Desktop VNet, with an Expressroute connection back to on-premises (Internal network).
    2- You have a UDR on that VNet with a default route 0.0.0.0 next-hop Internet.
    3- For one specific destination on the Internet you need traffic to be sent toward your On-Premises instead of directly toward the Internet, right?

    Could you try to create a UDR on the VNet with a next-hop of an IP address of your Internal Router/Firewall that is connected to the Internet, and since your VNet learned this route through the ExpressRoute BGP, it would use the ExpressRoute back to your On-premises.

    Let me know how it goes.

    All the best, and Stay strong!

    Cheers,
    Ahmed Muhi

  2. Diederik Janson 21 Reputation points
    2022-05-27T17:36:29.827+00:00

    Hi Ahmed,

    Our network partner managed to add the ip address to our internal bgp table and that worked.

    Thanx for your thoughts.

    Cheers,

    DJITS.

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