GRE tunnels not working between the Cisco CSR routers

Question

Hi experts,
I am testing in Azure. I am trying to build a GRE tunnel between two Cisco CSR instances but can't make it work... Is there any restriction on that communication or protocol from Azure?
Thanks!
Difan

Answer 1

@Difan Zhao Thank you for reaching out to Microsoft Q&A.

I understand that you have questions regarding buliding a GRE tunnel between CSR instances in Azure Virtual Network. However, Multicast, broadcast, IP-in-IP encapsulated packets, and Generic Routing Encapsulation (GRE) packets are blocked within VNets.

Checkout - What protocols can I use within VNets? for more details. Hope this was helpful.

Please let us know if you have any further questions and we will be glad to assist you further. Thank you!

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Answer 2

Had a similar issue recently, and I can confirm that GRE tunnel didn't worked between two Cisco CSRs within a single VNET. I Haven't tested between two different VNETs yet, may be it will work if traffic will leave from VNET to another and specially where the tunnel src/dst are public IPs.

Answer 3

Wow, that's so disappointing. IP-in-IP is still plain ip traffic. Why Microsoft should do anything with it?