Forum Discussion

Maria123's avatar
Maria123
Icon for Altostratus rankAltostratus
Dec 06, 2019

Diagnose the LB_FAILED Event

FB_FAILED is occurring even if all the server nodes are available. In the iRule logged the [event info] but noting is coming.

 

Is there any way to identify or diagnose the reason for this?

 

The tcp profile associated with the virtual server has "Maximum Syn Retransmissions" set to 3 currently.

 

The tcp monitor is having interval set to 5 secs and timeout set to 16 secs.

 

Will increasing the "Maximum Syn Retransmissions" or monitor timeout or interval improve on this?

 

application delivery
iRules
LTM
  • Lee_Sutcliffe's avatar
    Lee_Sutcliffe
    Icon for Nacreous rankNacreous
    Dec 08, 2019

    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.

     

    Try enabling auto-snat

     

    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

     

  • Sam_D_'s avatar
    Sam_D_
    Icon for Altostratus rankAltostratus
    Mar 25, 2020

    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's avatar
    skunk
    Icon for Nimbostratus rankNimbostratus
    Mar 10, 2021

    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!