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

DNS Resolution with the RESOLVER::name_lookup Command

When 15.1 released, we deprecated the RESOLV::lookup command. It still works, but there is no commitment that it will continue to work, so now is a good time to begin migrating your code away from it...
Published Jan 26, 2021
Version 1.0
application delivery
big-ip
irules
JRahm's avatar
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Christ Follower, Husband, Father, Technologist. I love community and I especially love THIS community. My background is networking, but I've dabbled in all the F5 iStuff, I'm a recovering Perl guy, and am very much a python enthusiast. Learning alongside all of you in this accelerating industry toward modern apps and architectures.
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Fabrizio66's avatar
Fabrizio66
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Feb 21, 2022

Hello, thank you for explanation, however I didn't manage to convert RESOLVER::name_lookup in my RESOLV::lookup iRule.

Below what I have:

when HTTP_REQUEST {
set client_IP [IP::client_addr]
set client_hostname [RESOLV::lookup @127.0.0.1 -ptr $client_IP]
HTTP::header replace X-Forwarded-For "$client_IP"
HTTP::header replace X-Forwarded-Host "$client_hostname"
#log local0. "Received XFF Host from $client_hostname"
HTTP::header insert IS_SSL "ssl"
#log
# }
}

Result

info tmm6[28816]: Rule /Common/incas-prod-pool_based_on_client_dns <HTTP_REQUEST>: Received XFF Host from - 10.8.4.42%5

Could you help me please? I upgraded from 14.1.2.8 to 15.1.5 and this irule doesn't work anymore, even if RESOLVER::name_lookup should be still supported with 15.x and 16.x.

Thanks

Regards.