Solved

Setting TTL for DNS Host

Posted on 2012-03-13
5
1,469 Views
Last Modified: 2012-08-13
I am in the process of setting up a second A record in my DNS for my domain name, my default TTL  is set for (7200) for my primary host IP but I’m trying to find a happy medium for the TTL so that it looks at the second IP before the web browser times out. As of now it reads

Primary:     www      .abc-123.com      TTL (7200)      IP (192.168.1.23)

Secondary:     www      .abc-123.com      TTL (7200)      IP (192.168.2.25)

 Any recommendations

Thanks
0
Comment
Question by:ahmad1467
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 3
  • 2
5 Comments
 
LVL 57

Accepted Solution

by:
giltjr earned 500 total points
ID: 37719592
The TTL has nothing to do with web browsers timing out and then going to the second address.

The TTL is how long that DNS entry should be cached by resolvers before being purged from cache and another DNS lookup is done.

That is, I lookup name www..abc-123.com and get back an address.  I keep that address in my cache for 7200 seconds (two hours).  After two hours I remove it from my cache and do another lookup the next time I need to visit that host.

I am assuming that you want a low TTL in an attempt to do load balancing?

If so, I would suggest you get a real load balancer.  The DNS Round robin method of load balancing is fine, until one of the servers goes down.  The DNS server will still return the IP address of the server that is down and so people will still try and go to it.
0
 

Author Comment

by:ahmad1467
ID: 37721302
I'm looking to have a low TTL to allow me a backup path to access the web site if the main IP address is not available.
0
 
LVL 57

Expert Comment

by:giltjr
ID: 37721359
O.K, as I stated in the 1st e-mail.  The only way that really works, is if you remove the "main" IP address from DNS.  As long as the IP address of the "main" server is in DNS, the server will respond with that address and the users will try to get it.

In fact there is no "main" and "secondary" addresses to DNS.  There is just a list of addresses.  The DNS server will hand it out in round robin form.  That is, 1st query get address #1, second query gets address #2, third query gets address #1, fourth query gets address #2, and so on.
0
 

Author Comment

by:ahmad1467
ID: 37721676
I’m sorry this is all new to me; I just want to make sure we are talking about the same DNS record.Is this the DNS A record for my domain name? In my setup I have a domain name configure with two IP address from two different providers. On my firewall I have both connections coming in then in my FW rules I have two different Net Trans pointing to the same web server. Would this be the same thing?

Thanks
0
 
LVL 57

Expert Comment

by:giltjr
ID: 37722087
Yes we are talking about A records.

You have a single A record with two IP addresses.  When I say "lookup hostname abc-123.com" the 1st time I will get back 192.168.1.23.  The next person will get back 192.168.2.25.  The next person will get back 192.168.1.23, and it keeps alternating.

If 192.168.1.23 goes down, the DNS server has no clue that it is down and will continue to respond with that address on every other query.  So every other person will attempt to connect to the IP address that is down.

Read on round robin dns here:

http://en.wikipedia.org/wiki/Round-robin_DNS
0

Featured Post

How Do You Stack Up Against Your Peers?

With today’s modern enterprise so dependent on digital infrastructures, the impact of major incidents has increased dramatically. Grab the report now to gain insight into how your organization ranks against your peers and learn best-in-class strategies to resolve incidents.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Occasionally you run into the website or two that will not resolve properly using your own DNS servers.  Some people simply set up global forwarders for their DNS server.  I don’t recommend doing this because it can cause problems resolving addresse…
Resolve DNS query failed errors for Exchange
Michael from AdRem Software outlines event notifications and Automatic Corrective Actions in network monitoring. Automatic Corrective Actions are scripts, which can automatically run upon discovery of a certain undesirable condition in your network.…
This is my first video review of Microsoft Bookings, I will be doing a part two with a bit more information, but wanted to get this out to you folks.

688 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question