DNS query for GTM & LTM based URL's

Hello

1) The DNS works with FQDN (fully qualified domain name) and no matter the URI. The DNS circuit don't care what you are trying to access on server ports e.g. HTTP, ICMP, FTP, etc.

Think DNS is like a address book that associate an address name to a ZIP code. Easier to remember address name than a list of IPv4 or IPv6 number, right?

2) If client won't cache, it will query to recursive DNS. If LDNS didn't have it localy cached, LDNS will query for DNS on BIG-IP.

E.g.:

If you have IPv4 and IPv6 enabled on you machine and you are trying to access a site that have just IPv4 address, you'll notice the following network activity (wireshark, tcpdump, etc):

Scenario:

Local machine: IPv4 and IPv6 address are set

FQDN: www.mysite.com at X.X.X.X (IPv4 only)

http://www.mysite.com/page.html

http://www.mysite.com/image.png inside page.html

1) At first query to www.mysite.com, your machine will ask for AAAA record (IPv6) address resolution.

2) It will get NOERROR from Authority server and no IPv6 to reach.

3) Still on first query, it will try www.mysite.com for A record (IPv4) address resolution.

4) The authority server "mysite.com" will reply an A record like this:

www.mysite.com 30 IN A X.X.X.X

5) So, your machine will store this A record X.X.X.X for 30s, and you will access the URL http://www.mysite.com/page.html

6) At second request (during 30 seconds TTL), your machine will ask for AAAA again.

7) Again no response for IPv6 address

8) Your machine will ask for A record and it is on local cache.

9) Your machine will get this address localy and request for the URL http://www.mysite.com/image.png

In this scenario, the machine will always try the IPv6 address first, but once for IPv4 during TTL (time to live) period.

I've draw this simple query flow to about basic DNS query.

I really hope it helps

Regards

Thanks Cjunior for your response, it really helps,

Please help me confirm the understanding,

I hit, www.mysite.com --> it goes from LDNS to GTM (SOA) --> I get a response back with LTM VIP,

Now i will connect to the vip direclty, it gives me a page,

now, i am in the application, i will go ahead and click a link within my application within 30 seconds (which is GTM pools TTL), www.mysite.com/report --> I understand, it will again make a DNS query for FQDN, but will pick the answer from cache as this is within TTL value,

Let's say, i stay inactive in the app for 60 seconds, then i try to click www.mysite.com/process --> it will do a DNS query again for FQDN, it will look at LDNS, which no longer have the cached value as TTL expired, it will go to SOA, F5 GTM for resolution, correct?

Conclusion: what i wanted to confirm is, even if i am navigating to different places within my app, every time, it will query DNS for the FQDN,

Thank you very much.

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?