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purna_256577's avatar
purna_256577
Icon for Nimbostratus rankNimbostratus
Oct 05, 2016

Need to know any possible way to clear cache/flush dns for a records on GTM/DNS where GTM act as forwarder for the query.

RX/vendor supplier changed the DNS records recently,We have situation where the TTL of DNS record expires in 86400 sec. BIGIP GTM is acting as forwarder for those records. When we clear cache on the forwarded DNS server , on BIGIP we are unable to see the change until TTL expires. So we need to know whether any way we can flush the DNS when the DNS queries is been forwarding to other DNS server.

 

ON GTM configured forwarder. zone "." { type forward; forwarders { x.x.x.x; }

 

BIG-IP DNS
devops
security

2 Replies

  • Samir_Jha_52506's avatar
    Samir_Jha_52506
    Icon for Noctilucent rankNoctilucent
    Oct 05, 2016

    Option is there on F5 GTM but haven't use any more. Please find below link

     

    https://support.f5.com/kb/en-us/products/big-ip_gtm/manuals/product/gtm-implementations-11-2-0/12.html

     

    Hope article will be helpful.

     

    Thanks

     

  • John_Heyer_1508's avatar
    John_Heyer_1508
    Icon for Cirrostratus rankCirrostratus
    May 03, 2017

    Is the forwarder setup in Zones -> ZoneRunner -> Zone List? If so, it's using the BIND/NAMED backend. This TMSH command will restart it and thus drop all cached records:

    restart /sys service named

    You can also have the forwarder not cache at all by using the "forward only" option. Example:

    zone "whatever.com." {
    type forward;
    forward only;
    forwarders {
        192.168.1.1;
        192.168.2.2;
    };
};

    However, you probably wouldn't want to apply this to "." since that would disable caching for general queries.

    Bottom line - whoever is controlling that records should consider lowering the TTL. 86400 seconds is 1 day, and most people are using 1 hour or even 1 minute.