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