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Kevin_Nail's avatar
Kevin_Nail
Icon for Nimbostratus rankNimbostratus
Feb 09, 2007

DNS iRule questions

I am running GTM v 9.2.3 and have a question about using an irule to accomplish what I want to do...

 

 

We have a disaster site downtown that is up and running with LTM's in front of our apps. We have a wideip set up on the GTM that contains the downtwon virtual server and the local virtual server in a pool. DNS resolution works correctly with 1 or the other IP being handed back.

 

 

The problem is with DNS caching at the local browser level where the first IP handed back gets cached and then subsequent requests resolve to the same place even if that IP is down.

 

 

Is there a way to mitigate this problem with an iRule on the GTM? In other words, I would like for the end user to always get the same IP resolved but behind the scenes the traffic is going to the server that is up.

 

 

Forgive my ignorance but any help is appreciated.
application delivery
dev
devops
iRules

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  • JRahm's avatar
    JRahm
    Icon for Admin rankAdmin
    Feb 12, 2007
    GTM is a fancy DNS box. After all the intelligence, only one thing happens, an IP address (or more, depending on configuration) is returned to the device that requested one. So if DataCenter1_vip is down, and the local dns server of the client has that address cached for 10 minutes, then all clients utilizing that ldns will be down for the remaining TTL. That downtime can be mitigated on the LTM hosting that *down* service if the path to it from the client is still up (ie, only the application itself has failed, the infrastructure is still intact). On the LTM, you could redirect traffic over to the other site, either by configuring the http profile with a fallback host, or if the logic is more complicated, utilize an iRule.
  • James_Thomson's avatar
    James_Thomson
    Icon for Employee rankEmployee
    Feb 12, 2007
    This can only be solved at the BIG-IP LTM level with redirects or Route Health Injection.