icecarDisaster recovery.  Two words that can make even the most experienced of us cringe.  It’s DR, it’s a backup site, it’s a quasi-failover-but-not-quite-a-disaster-site… I don’t always drink DR, but when I do I prefer f5 GTM.

With half of the country being subjected to below zero temps and covered in ICE, I thought it would be a good time to bring up the fact that f5’s GTM module has a handy little feature that is not often discussed.  I have found that it is a tremendous time saver (you don’t have to use priority load balancing to juggle your GTM pools/members) and it’s easy to setup.  The feature I am talking about is referred to as the “Last Resort Pool”.  When everything else is down the Last Resort Pool is what gets served up.

Speaking of setup, here is a little background on our setup to begin with.  We have three GTM 1600 units, each sits on it’s own ISP carrier.  NS1 and NS2 are our primary DNS servers which are at the home office and NS3 that is at the DR site is our tertiary DNS controller.  All f5 devices are running TMOS version 10.2.4.

The first thing that you want to do is pick the Wide IP that you will be working with.  Go to the pool that you have setup for that Wide IP and click on the Members tab.  Under the Load Balancing Method change the Fallback method to “None”


Then create a pool that contains the external IP’s of the servers that are out at your DR site.  We will call this pool “www.com_dr_pool”.  With that created go to the Wide IP List and select the Wide IP that you created the DR pool for.  There under General Properties you will find an option labeled “Last Resort Pool”.  Just use the drop down menu and select your newly created DR pool and you are done!


When all of the pool members for your Wide IP are down the GTM will serve up the DNS address of whatever is in the last resort pool.  When your production Wide IP Members come back online it will revert to handing back out those addresses and stop passing out the address of what is in the Last Resort Pool.


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