Azure LoadBalancer blocks a local vnet connections

Question

Why after adding a Windows VM to a SKU Standard Load Balanacer backend pool, the VM is not accessible by a sibling vm on the same vnet using

telnet localip 3389

It wrote: "No route to host"

If the VM is removed from the backend pool, the connection was successful.
At the VM's nsg there is rule to allow 3389.
The outbound configuration at the LB has a rule to automatically distrubute the ports (SNAT).

Answer 1

Hi @Jan Vávra

Good day!

I have set up a lab and initiated a test where I deployed VM in the backend pool of the public load balancer and tried to telnet to a sibling VM in the same VNet. I was able to successfully telnet to the VM in the load balancer.

I tried the telnet vm in the backend pool of the load balancer.

This may be the reason why you are unable to access the VM in the backend pool of the load balancer.

Refer this link :

https://learn.microsoft.com/en-us/azure/virtual-network/virtual-network-troubleshoot-connectivity-problem-between-vms#step-5-check-whether-the-problem-is-caused-by-snat

If you have any further queries, do let us know.

Thanks,

Rohith

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