Azure Service Bus EndpointNotFoundException from certain environments

Question

Hi experts,

We use an Azure Service Bus to connect a cloud app to on prem environments with a WCF relay service. We use this for dozens of environments, but for some environments the connection cannot be established. What we did on that environment:

1. Checked port settings: https://learn.microsoft.com/en-us/azure/azure-relay/relay-port-settings#wcf-relays
2. Checked IP settings: https://learn.microsoft.com/en-us/azure/service-bus-messaging/service-bus-faq#what-ip-addresses-do-i-need-to-add-to-allow-list-
3. Followed the troubleshooting guide: https://learn.microsoft.com/en-us/azure/service-bus-messaging/service-bus-troubleshooting-guide --> all tests success, tnc commands succeed, service bus can be reached

However, when we test the connection on that specific environment, it returns an endpoint not found exception. If we run the exact same service on a different environment with the same settings, it perfectly connects. We do not have firewall settings on our service bus. So it looks like "something" on that specific environment is still blocking the traffic to the service bus, but since the troubleshooting guide succeeds we are out of options what it can be.

Does anyone have any suggestions? Thanks a lot for any advice!

Answer 1

@Rogier Haest Can you confirm what was the port number you have performed the test? As the service bus document talks about 5671,443,5672 but depending upon the type of WCF relay binding you are using you can refer to this document for the port number that you need to perform the test.

You can do the nslookup on the namespace name to know the IP address of your namespace name i.e. nslookup yournamespacename.servicebus.windows.net
You can also use Port Query Tool to test the IP address along with the port number to verify if the connection is blocked at your client network.

If the above test are passed then you can use netmon traces to reconfirm whether your application is connecting to the same port/IP address for which you have performed the test. The suggestion would be engaging your network team to assist you further.