GTM/DNS as a smart DNS server ("without" LTM)

[SMilanic]

Hi,

I am trying to figure out a way to use F5 BIG-IP GTM/DNS as a smart DNS server only. The idea is shown in the figure below.

There a two data centers with GTMs, LTMs and servers as shown above. Let's just say that we don't want to place the servers "behind" the LTMs (and forget for a sec all the good reasons why they should be behind an LTM) from a client's perspective.

The client would like to access a service at a fqdn. The LDNS queries one of the GTMs. A GTM returns the IP of one of the SERVERS, NOT a VIP. The GTM also needs to know if the servers are UP, so some form of monitoring is required (probably done by an LTM). Load balancing is also required, but a simple Round Robin would do.

I haven't found an elegant way how to accomplish this yet, perhaps this can be achieved with an iRule?

Any ideas appriciated!

[Nikoolayy1]

F5 GTM(DNS) can work directly with 3-rth party servers without LTM and you may use health monitors like SNMP or ICMP or HTTP/HTTPS for the monitoring:

https://techdocs.f5.com/kb/en-us/products/big-ip-dns/manuals/product/bigip-dns-implementations-12-1-...

Better to also configure a prober pool to select which BIG-IP devices (LTM or DNS/GTM) will send the probes to the generic hosts as otherwise the F5 devices will use and automatic algoritam to delegate the monitoring to one of them that will inform the other F5 devices if the servers are up:

https://support.f5.com/csp/article/K08433560

https://support.f5.com/csp/article/K10385

You can use DNS irules to make more specific logic like for specific client ip addresses or hostnames to return the pool with generic  host servers and not the one with LTM Virtual servers:

https://community.f5.com/t5/technical-forum/gtm-irule-to-set-the-pool-based-on-which-gtm-is-respondi...

https://clouddocs.f5.com/api/irules/DNS_REQUEST.html

[SMilanic]

Hi, Nikoolayy1,

thank you for your reply! It seems that "Generic Host" server type offers the options I need. I will look into it. Thanks!

[Nikoolayy1]

I hope that it is the solution you are searching for. After you have tested, you can share with us so we can close this post.