Diagnose the LB_FAILED Event

Question

FB_FAILED is occurring even if all the server nodes are available. In the iRule logged the [event info] but noting is coming.&nbsp;Is there any way to identify or diagnose the reason for this?&nbsp;The tcp profile associated with the virtual server has "Maximum Syn Retransmissions" set to 3 currently.&nbsp;The tcp monitor is having interval set to 5 secs and timeout set to 16 secs.&nbsp;Will increasing the "Maximum Syn Retransmissions" or monitor timeout or interval improve on this?&nbsp;

lee_sutcliffe · Answer

make sure your pool members have a route back via F5, sounds like a routing issue. LB_FAILED happens when the TCP handshake to the pool member is not completed successfully. &nbsp;Try enabling auto-snat &nbsp;I’m guessing you are using gateway_icmp as a health monitor (which is connectionless). This will mark your pool up, however a TCP connection might fail as it require a working return path via the F5&nbsp;

sam_d_ · Answer

Hei Maria, we are now encountering the similar issue where BigIP works as load balancer before 3 LDAP servers. It'll be really appreciated if you could share your solution with me. Thanks in advance!

skunk · Answer

Hello Maria, We do have the same situation here: all PoolMember show UP, iRule event LB_Failed gets triggered and Event_Info is empty :-(Max_Syn_Retransmit is set to 5 - no difference.We do SNAT, so return path is fine ...Could you please share your solution? Thanks in advance!

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