Question on Cname in DNS

[harveymasons]

I am trying to undersrtand how a Cname record works in DNS?

I was told a Cname is an alias to a real host name.

CAn someone give an example of how and or why a Cname would need to be used??

thx in advance,

harvey

 

[Wishdiak]

harveymasons,

I'll try to find you a link to some good, simple documentation online, but in the meantime, here's a simple explanation.

Say you have a DNS zone for xyz.com. Within xyz.com, you have a few hosts: server1, server2, etc. These would be A records in the xyz.com zone.

Now, you want to have a DNS record for

http://www.xyz.com

and have it point to server1.xyz.com. How do you do this? With a CNAME record that aliases the host

http://www to

host server1.

Wishdiak
A+, Network+, Security+, MCSA: Security 2003

http://www.wishdiak.com

 

[dpoulson]

To elaborate:

Suppose you set up your web server on server1, but set up a CNAME of

http://www pointing

to server1 and publish your web address as

http://www.xyz.com.

server1 blows up and you quickly set up the web site on server2, then rather than telling everyone a new address, you simply change the CNAME entry to point to server2.

Also, if you have a mail server, you can reference it as imap.xyz.com, pop3.xyz.com and mail.xyz.com for imap, pop3 and smtp services. At a later date you can then split them up onto different servers to spread the load.

Lastly, you can do a very crude loadbalancing by setting up multiple CNAMES to different servers, eg you have 3 CNAME entries for www, pointing to server1, server2, server3. DNS will then do a round robin load balancing, directing the first request to server1, the second to server2, etc.

HTH

Darren.

 

[ChrisAC]

Suppose you set up your web server on server1, but set up a CNAME of

http://www pointing

to server1 and publish your web address as

http://www.xyz.com.

server1 blows up and you quickly set up the web site on server2, then rather than telling everyone a new address, you simply change the CNAME entry to point to server2.

Using a CNAME here would be of no benefit at all. If you didn't use a CNAME there would be nothing stoping you from simply changing the IP address of the A record for www. Even with a CNAME there has to be an A record somewhere down the line.

Chris.

**********************
Chris A.C, CCNA, CCSA
**********************

 

[GlenJohnson]

Just read this. Simple google search found it. Good luck,

http://www.rscott.org/dns/

and look at step 6.

Glen A. Johnson
If you're from the Illinois, Wisconsin or Florida area, check out Tek-Tips in Chicago IL
To get the best answers to your questions, check out faq950-5848

 

[harveymasons]

Thanks alot guys. I Really appreciate it.

I understand it much better now.

thanks again,
HArvey