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I have two Windows 2012 servers, joined in a Windows Network Load Balancing cluster. I have been trying to find how the NLB heartbeat message is exchanged between those servers (to make sure it will not be blocked by anything on the production system), but have not been able to find any information.

On my test system, I have not been able to see the heartbeat message in Wireshark on either of the two servers.

So the question is - do I need to open any ports in the firewall for the heartbeat messages (or any other service messages required for the NLB to work)? How are the heartbeat messages exchanged?

Thank you!

rinspy
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2 Answers2

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NLB operates at the Ethernet layer, which is below the whole TCP/IP stack and thus below any firewall. And, anyway, NLB hosts must be connected to the same network segment: there can't possibly be any block between them.

Massimo
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NLB heartbeats operate at Layer 2, so no firewall ports need to be opened.

Here's a screenshot of an NLB heartbeat, captured with Microsoft Network Monitor:

enter image description here

joeqwerty
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