Is vnet peering transitive by default?

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Is vnet peering transitive by default?

AZLearner 96

This is about Azure only, no S2S to on-prem. I have a hub-and-spoke topology where vnet A is the hub and vnet B & C are the spokes. Vnet peering is set up between A & C as well as A & B. Does it imply by default resources in B & C can reach each other?

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GitaraniSharma-MSFT 50,096 Microsoft Employee Moderator

Hello @AZLearner-5762 ,

No. Transitive peering is not supported. You must peer VNetB and VNetC for this to take place.
Please refer : https://learn.microsoft.com/en-us/azure/virtual-network/virtual-networks-faq#if-i-peer-vneta-to-vnetb-and-i-peer-vnetb-to-vnetc-does-that-mean-vneta-and-vnetc-are-peered

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Olivier Dupré 6 Reputation points

2021-10-27T07:39:17.32+00:00

You can make it transitive. You simply need to add:
* a "Virtual Network Gateway" in your hub,
* a "Gateway Subnet" in your hub,
* A Route Table to each of your B and C subnets with route to other VNet CIDR and next hop on the Virtual Appliance automatically deployed in the "Gateway Subnet". eg: If you declare a "GW Subnet" with the CIDR 10.0.0.0/16, then it has, by default a Virtual Appliance on 10.0.0.4.
Amit Misra 0 Reputation points

2024-02-14T06:51:09.76+00:00

Is it still true? Transitive traffic flow can be achieved using below setting and NVA/UDRs https://learn.microsoft.com/en-us/azure/virtual-network/virtual-network-manage-peering?tabs=peering-portal#create-a-peering Allow gateway in 'vnet-1' to forward traffic to 'vnet-2'
GitaraniSharma-MSFT 50,096 Reputation points Microsoft Employee Moderator

2024-02-14T15:50:36.9766667+00:00

@Amit Misra, yes, it is still true for the setup where you only have Vnets without any gateways or route servers. If you have gateways or route servers, then transit connectivity is possible using UDRs. The question asked in this thread was if Vnet peering is transitive by default, which is not true even today. By default, it is not transitive.

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Is vnet peering transitive by default?

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