Mar 27, 2026 - For details about updated CVE-2025-53521 (BIG-IP APM vulnerability), refer to K000156741.

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nvhoanhai's avatar
nvhoanhai
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May 21, 2026

about create wide ip,

i create generic host (Firewall) server and virtual server for wide ip,
i use health monitor is gateway_icmp but server and virtual server It keeps flapping between up and down, and the status is unstable.
i was cli device F5 ping test to device generic host ok, its ok, its dont have lost or packet loss
can you help me check issue

1 Reply

  • The flapping you’re seeing with GTM Wide IP using a gateway_icmp monitor is usually because GTM health checks behave differently from manual ping—factors like aggressive default intervals, multiple GTM devices probing inconsistently, firewall ICMP rate-limiting, or source IP differences can cause intermittent failures even when basic connectivity looks fine; since ICMP only checks reachability (not service health), it’s often unstable for this use case, so tuning the monitor or switching to a more reliable protocol-based check is the recommended approach.

     

    few other Solutions to explore further:

     

    1. Tune ICMP monitor: Increase interval/timeout to reduce sensitivity and avoid false downs.

    2. Use TCP monitor: Check a port (e.g., 443) for more stable and meaningful health status.

    3. Use HTTP/HTTPS monitor: Validate actual application response instead of just reachability.

    4. Adjust quorum (multi-GTM): Prevent a single failing probe from flipping overall status.

    5. Check firewall policy: Ensure ICMP from GTM is not rate-limited or blocked intermittently.

     

    #################

     

    Is there any possibility of using TCP monitor instead of ICMP, as TCP is minimum best for firewalls

     

    If behind firewall:

    Use HTTP/HTTPS monitor (if applicable)

     

    Can you check and tell:

     

    Is ICMP rate-limited?

    Is GTM self-IP allowed?

    Any IPS/DoS protection?

     

     

    Avoid gateway_icmp for Wide IP health checks

     

    its better to use

     

    TCP monitor (minimum)

    HTTP/HTTPS monitor (ideal)

     

     

    If you want, share:

     

    Your GTM topology (single / HA / multi-site)

    Monitor config output (tmsh list ltm monitor)

    tmsh show gtm server

     

    I can dig further and will try to pinpoint the exact root cause in your setup.