Multiple Expressroutes From Different Vendors - Route Redistribution

Daryl W. Clark 1

We have a customer that has a private MPLS WAN from one of the big telecom providers connecting all their remote sites back to Azure over Expressroute and a VNG. They are looking to connect a couple of 3rd party vendors over new Expressroutes from them into Azure but want some level of network segmentation between them.

If they had a new Expressroute circuit from Vendor A installed to their tenant and then connected it to the existing VNG for their corporate WAN, would routes be automatically shared between the two circuit or would they need to redistribute them via something else? Ideally, they would NOT be shared between providers as Vendor A should not have routing updates from corporate WAN and vice versa. The expense with running a separate VNG for each 3rd party vendor would become cost prohibitive, especially since many of the circuits they're looking to migrate are <10Mbps.

TIA in advance, I wasn't able to find any information when I searched for this.

GitaraniSharma-MSFT 49,171 Reputation points Microsoft Employee

2021-03-10T10:55:54.127+00:00

Hello @Daryl W. Clark ,

Thank you for reaching out & hope you are doing well.

I would like some more details on your existing setup & requirement to fully understand the ask. But as far as I understood, your ask is something as below:

If 2 circuits are connected to same Vnet & ExR gateway, what would be the route distribution, is that correct?

Thanks,
Gita
Daryl W. Clark 1 Reputation point

2021-03-10T15:04:09.137+00:00

Sorta...

ExpressRoute 1 is connected to Contoso On-Premise Network

ExpressRoute 2 is connected to Vendor X to delivery direct connectivity for Service Y (replacing an existing physical connection into the on-prem data center)

Are the routes learned on ExpressRoute 1 redistributed to ExpressRoute 2 and vice versa?
GitaraniSharma-MSFT 49,171 Reputation points Microsoft Employee

2021-03-10T16:17:06.497+00:00

@Daryl W. Clark , if your ask is "will on-perm routes from ExR1 be advertised to ExR2 & vice versa", then NO. Unless the circuits are connected to each other via ExpressRoute Global Reach.
ExpressRoute cannot be configured as transit routers.
Refer : https://video2.skills-academy.com/en-us/azure/expressroute/expressroute-routing#transit-routing-and-cross-region-routing

But if both the circuits exist in the same on-prem location(with same address prefix) and are connecting to the same Vnet, then it could lead to asymmetrical routing.
Please refer : https://video2.skills-academy.com/en-us/azure/expressroute/designing-for-disaster-recovery-with-expressroute-privatepeering
GitaraniSharma-MSFT 49,171 Reputation points Microsoft Employee

2021-03-15T08:24:05.417+00:00

@Daryl W. Clark , Kindly let us know if the above helps or you need further assistance on this issue.
GitaraniSharma-MSFT 49,171 Reputation points Microsoft Employee

2021-03-18T14:47:40.933+00:00

@Daryl W. Clark , I'm following up again to check if the above helps or you need further assistance on this issue.
GitaraniSharma-MSFT 49,171 Reputation points Microsoft Employee

2021-03-24T14:03:55.227+00:00

@Daryl W. Clark , any further updates on this post?

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Multiple Expressroutes From Different Vendors - Route Redistribution