Why I am able to Telnet to VIP when pool members are down ??

Hi,

Main issue with testing VS (one with HTTP profile assigned) via telnet is how Standard VS handles new connection:

• 3WHS is always performed
• VS is waiting for first HTTP request from client before selecting member and performing 3WHS on server side.

Now, if you are sending any data using telnet (like pressing any key when telnet session is open) VS will be sending ACK but not doing anything else (except resetting I Idle timeout on created client side flow).

If you will handle telnet session close gracefully (ctrl=] then quit) VS will even perform proper 4WC (FIN-ACK exchange).

So everything looks OK considering telnet, but proofs nothing.

Even worse, when using

show ltm profile tcp 

What will happen depends as well on Verified Accept enabled - you will get immediate RST (not recommended for HTTP type VSs).

As already mentioned a lot depends on VS config, for example Standard VS without HTTP profile immediately respond with RST, when checking

show net rst-cause

So conclusion is that only way to test is to send at least one HTTP request after 3WHS and better use tools like curl for testing.

Piotr