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I have a client that makes HTTP post requests to an F5 load balancer.

I usually only have two to three servers connect to the load balancer endpoints. But I don't have access to the F5.

How can I find out the IP address of even one server that connects to the load balancer? It is helpful when I need to quickly bypass the F5 to make sure the problem is not at the F5 layer.

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If you are required to troubleshoot through the load balancer, you will have been given the IP's of the servers on the other side of it. Those IP's won't change (they'll either be static private IP's or static public IP's). What kind of situation would have you troubleshooting servers with IP's that you don't know? – Everett Jul 23 '12 at 5:26
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The F5 distributes connections to the servers - they should be oblivious to the fact they are part of a pool, and the client cannot know. The only device that can know is the F5 itself. The only way I can imagine you could do this is to look at where the connections come from on the servers - if they are sourced from the IP address of the F5, then you know they are part of a pool. – Paul Jul 23 '12 at 5:26
if you don't have access to the F5? do you have access to the servers behind it? If not, the only way you are going to find out the IP of the servers is to probably ask the server admins. Also it might not be possible to gain access directly to the servers depending upon how the f5 is configured (It could be NAT'ing to them, and they might not allow Direct access) – Doon Jul 23 '12 at 5:31
Consider also: Sometimes a load balancing appliance provides services other than just load balancing requests. For instance, folks often use the F5 for SSL (HTTPS) acceleration, meaning the web servers only see plain HTTP requests from the F5 even though the client may send HTTPS requests. This may complicate bypassing the load balancer in the way you're thinking. – Chris W. Rea Jul 25 '12 at 17:34
p.s. Isn't this more appropriate for Server Fault? – Chris W. Rea Jul 25 '12 at 17:34
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closed as off topic by Chris W. Rea, Renan, slhck♦ Jul 25 '12 at 18:57

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Thank you for clearing that up Paul. The Security side of my brain flipped out for a second. Is there a chance that you could have a script placed on the servers to have them connect to a secured server and update their IP address with an offsite server that the network manager controls? The script could be set to fire if the IP address changes. Imagine it working like DynDNS does. Then you are having the servers identify themselves to your "shop," and the client doesn't have the IP addresses.

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