Does LB_Failed have the same criteria as using an HTTP Fallback Host?

Hi Chris,

 

 

See the LB_FAILED wiki page for details. What do you have the max syn retransmits set to on your TCP profile? Let me know if the LB_FAILED info doesn't match up with what you're seeing in your TCP profile(s).

 

 

 

http://devcentral.f5.com/wiki/iRules.lb_failed.ashx

 

 

LB_FAILED is triggered when LTM is ready to send the request to a pool member and one hasn’t been chosen (the system failed to select a pool or a pool member), is unreachable (when no route to the target exists), or is non-responsive (fails to respond to a connection request).

 

 

If the target fails to respond to a connection request, the "Maximum Syn Retransmissions" option in the TCP profile will affect the amount of time before LB_FAILED is triggered.

 

 

When a client doesn't receive a response to the SYN, there is a defined algorithm for the specified number of re-tries. First retransmission if no response is typically 3 seconds, and typical back-off timer algorithm is to double the wait time after each failed attempt.

 

...

 

LTM's default tcp profile sets "Maximum Syn Retransmissions" to 4, so with the default setting, LB_FAILED would be triggered if server didn't respond in 45 seconds:

 

 

11st SYN: 0

 

2 2nd SYN: +3 seconds

 

3 3rd SYN: +6 seconds

 

4 4th SYN: +12 seconds

 

5 5th SYN: +24 seconds

 

6======================

 

7LB_FAILED: 45 seconds

 

 

 

Aaron