Forum Discussion

sathish_2826's avatar
sathish_2826
Icon for Nimbostratus rankNimbostratus
Apr 24, 2020

DNS query for GTM & LTM based URL's

Hi there, I have couple of questions, my URL is load balanced between two LTM's and one GTM on top of it, so when i hit the application in the browser, it goes to DNS, DNS delegates to GTM for reso...
application delivery
BIG-IP
LTM
sathish_2826's avatar
sathish_2826
Icon for Nimbostratus rankNimbostratus
Apr 24, 2020

thank you, one last question,

 

If my GTM pool TTL is 600 seconds, and i connect to my app, and GTM sends a response to DNS with an LTM vip with a timestamp of 600 seconds, now if the resolved vip go down (status wise) anytime during the 600 second window, will DNS know of that, or will it continue to direct me to the unavailable vip?

cjunior's avatar
cjunior
Icon for Nacreous rankNacreous
Apr 24, 2020

Hi,

If your VS goes offline, the customers who got the previous available IP will fail until the TTL expire or cache flushes.

You should consider setting lower values ​​for TTL to have high availability for your application.

 

Regards

  • sathish_2826's avatar
    sathish_2826
    Icon for Nimbostratus rankNimbostratus
    Apr 29, 2020

    One last question, If i enable the wideip persistance ttl to 3600 seconds (default), and i have one pool associated to it, which contains 2 LTM vip's, inside the pool, i set the TTL to 30 seconds, and i select round robin,

     

    Please help me understand this, so this means, wideip persistance ensures i get the same pool member for 3600 seconds for DNS queries, and pool TTL ensures that even though i persist for the same IP for 3600 seconds, the client must do a fresh DNS query every 30 seconds so that if the member that i was persisted to went down, the over all GTM persistance gets rewritten with the new member,

     

    Can you confirm this please.

  • cjunior's avatar
    cjunior
    Icon for Nacreous rankNacreous
    Apr 30, 2020

    Hi,

    When query response are persisted, LDNS/client (an IP range) will get same resolved IP during this persistence validity.

    When you check to persist to WideIP and keep "Verify Member Availability" on pool marked, in case of persisted member goes unavailable during ttl persistence, BIG-IP should reselect a new member.

     

    So, a DNS record TTL is to cache responses on client and TTL persistence is a BIG-IP DNS feature to keep clients routed to destination address they first got.

     

    For more: 

    https://support.f5.com/csp/article/K15594

     

    Regards.