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igor_'s avatar
igor_
Icon for Cirrus rankCirrus
May 12, 2025
Solved

F5 ERR_CONNECTION_RESET

Hello, We are trying to expose our backend application, which is behind a Windows IIS reverse proxy. Based on URL rewrite rules which look for host header and than route the call to the backend. Wh...
application delivery
devops
  • Tofunmi's avatar
    Tofunmi
    May 12, 2025

    Did you take a packet capture? You should see the reason for the reset on the capture.

    tcpdump -nni 0.0:nnnp -s0 host X.X.X.X and port XXXX -w/var/tmp/capture.pcap

    Enabling these could help as well.

    1. Log in to the TMOS Shell (tmsh) by entering the following command:tmsh
    2. To configure the BIG-IP system to log the TCP RST cause in the /var/log/ltm file, you must enable the TM.RstCause.Log database variable by entering the following command:modify /sys db tm.rstcause.log value enable
    3. Optional: To configure the BIG-IP system to include the RST cause information in the TCP RST packet payload, you must enable the TM.RstCause.Pkt database variable by entering the following command:modify /sys db tm.rstcause.pkt value enable

    https://my.f5.com/manage/s/article/K13223

     

igor_'s avatar
igor_
Icon for Cirrus rankCirrus
May 12, 2025

Thanks, there was an error on the network side. After fixing the app was back online.

 

BR,

Igor