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

Forum Discussion

AndyBaba's avatar
AndyBaba
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Feb 24, 2022

Outgoing ICMP & DNS queries to public IP

Hey all i have 2 internet facing f5 ltm, I am seeing my f5 which has public IP on self ip is sending icmp queries & dns queries to public IP on internet. When we did a basic traffic capture, we see ...
big-ip
LTM
security
JoshBecigneul's avatar
JoshBecigneul
Icon for MVP rankMVP
Feb 24, 2022

Hi AndyBaba,

Can you tell me if this is for the main system DNS lookup service (System -> Configuration -> Device -> DNS) or is this for a DNS service referenced by a LTM pool?

You might consider checking out the article about management routing here: https://support.f5.com/csp/article/K13284

There is also an article that discusses scenarios where the traffic may appear to originate from the wrong interface: https://support.f5.com/csp/article/K10239 

Another feature that could be in play is the DNS Resolver feature which if memory serves will primarily use TMM interfaces to pass traffic instead of the management interface: https://support.f5.com/csp/article/K12140128 

My first bet would be a routing table issue, you should verify that piece first and make sure that a route exists to your internal IP.

Thanks,
Josh Becigneul

 

AndyBaba's avatar
AndyBaba
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Mar 04, 2022

Hi JoshBecigneul 

Thank you for the articles. It doesn't add up to any of the resolutions mentioned in them

In our LTM, i see the problem of LTM sending ICMP echo request & DNS query at same time public IP - which we dont recognize. The pattern of public IP keeps changing. And I believe, since our Firewall may have restriction - the responses are not received on F5.

We are trying to find why LTM is sendig queries out.

 

 

 

 

  • JoshBecigneul's avatar
    JoshBecigneul
    Icon for MVP rankMVP
    Mar 04, 2022

    Hi AndyBaba, i think you might be best to open a ticket with F5 Support to see if they can assist. Otherwise I'd suggest reviewing all pool memberships related to this, as well as check the virtual servers SNAT settings. Depending on how those are set, it could influence which source IPs get used. There are also services on the F5, like Phone Home that may need to make connections to the F5 cloud if they are enabled. https://support.f5.com/csp/article/K15000

    Thanks.