Azure Traffic Manager subnet routing not working.

Akash Acharya 0 Reputation points
2024-10-18T13:44:36.4333333+00:00

I am currently setting up an Azure Traffic Manager to DNS load balance between two endpoints using subnet routing. I have configured the Traffic Manager with two endpoints and specified the CIDR range containing my public IP address for one of the endpoint’s subnet configurations.

Issue: Despite this setup, my DNS lookup does not resolve to the intended target. I suspect that the DNS resolver’s IP might be the one which is detected and it resolves to fallback endpoint. I have also attempted using **`dig

Azure Traffic Manager
Azure Traffic Manager
An Azure service that is used to route incoming network traffic for high performance and availability.
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  1. VIVEK DWIVEDI 105 Reputation points Microsoft Employee
    2025-01-30T02:49:59.1033333+00:00

    Hello @Akash Acharya ,

    I hope you are doing great!

    To make it short, what you are suspecting is right. In case of subnet routing, Traffic manager mostly checks the recursive DNS resolver IP and not the end user IP unless it passed on the EDNS.

    You can also check if a client is ECS-supported by running either of the following DNS queries.

    nslookup -q=txt o-o.myaddr.l.google.com
    

    Below indicates that the LDNS IP is 20.48.x.x, and the ECS-supported IP is 60.77.x.x. Traffic Manager would use the ECS-supported IP for routing.

    Server:  dns.google
    Address:  8.8.8.8
    
    Non-authoritative answer:
    o-o.myaddr.l.google.com text =
    
            "20.48.x.x"
    o-o.myaddr.l.google.com text =
    
            "edns0-client-subnet 60.77.x.x/24"
    
    

    The same can also be checked by using dig:

    dig +short TXT o-o.myaddr.l.google.com
    

    Please let me know if this helps by accepting the answer.


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