Propagated Gateway Routes

Question

When selecting to enable of propagated routes for a route table, does this override all UDRs in the route table? I am trying to override the default route but its always selected as None when I try to forward it to another destination.

Answer 1

Hi ,

When you select NO to the Propagate gateway routes, then routes which are learnt by the Azure from On-Prem via BGP will discarded.

Regarding the routing precedence, UDR always takes the maximum presidence.

Regards,

Karthik Srinivas

Answer 2

@Steven J. Williams

Based on your questions above.

When selecting to enable of propagated routes for a route table, does this override all UDRs in the route table?

This will depend as Azure selects a route based on the destination IP address, using the longest prefix match algorithm. So, in the case above if the propagated route is more specific then it will be selected instead of the UDR.

When you exchange routes with Azure using BGP, a separate route is added to the route table of all subnets in a virtual network for each advertised prefix. The route is added with Virtual network gateway listed as the source and next hop type.

If multiple routes contain the same address prefix, Azure selects the route type, based on the following priority:

1. User-defined route
2. BGP route
3. System route

This is currently documented here.

I am trying to override the default route but its always selected as None when I try to forward it to another destination.

In this case you can create a UDR route with the same prefix to override the default route.

Hope this helps! Please let me know if you have any additional questions.

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