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

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2funky_105078's avatar
2funky_105078
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12 years ago
Solved

GTM: avoiding flapping DNS answers with RTT method

I am in the need to understand how GTM metrics work for GTM LDNS probes.   1) how they can be logged the decision? I am using 11.2 but moving fast to 11.4.1.. :)   2) Lets make an example. if...
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  • Cory_50405's avatar
    Cory_50405
    12 years ago

    The only solution I could see in your situation is to break your single pool into three pools, and either stick with RTT and enable persistence at the wide IP, or switch to topology. Either one should get you some more consistency.

     

Cory_50405's avatar
Cory_50405
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12 years ago

RTT load balancing is always going to return the answer with the lowest RTT independent of previous results. The amount of time that an answer will remain in an LDNS cache will depend on the TTL you are setting on the GTM. That is if the LDNS respects the TTL, which some do not.

 

If you are looking for more reliability with regards to resolving DNS queries to data centers/servers/etc. within a certain region, you may want to explore topology based load balancing. You can use it to direct users from countries/regions/states to data centers/pools/etc based on geographic location.

 

http://support.f5.com/kb/en-us/products/big-ip_gtm/manuals/product/gtm_config_guide_10_1/gtm_topology_newest.html