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DNS Round Robin

Posted on 2009-02-19
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Last Modified: 2012-05-06
If you have multiple web servers and you want to load-balance between them, I guess DNS Round Robin is an option to go for.
If so Can someone put some snapshots on how to configure that on windows DNS?

Thanks
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Question by:jskfan
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bswinnerton earned 920 total points
ID: 23688459
It's very simple. Just make duplicate records :)

Picture-1.png
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by:omarfarid
ID: 23688535
basically you need to add the same record (e.g. www) with different IP addresses
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by:Steve
Steve earned 160 total points
ID: 23689300
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Author Comment

by:jskfan
ID: 23691431
I don't have DNS installed on my computer, but I remember there is a checkbox for it and you enter your Webservers IPs in a list, and when the client request comes up the first IP on the top of the list is serviced to the client then that IP moves to the bottom of IPs list and the second on the list will be serviced to the next request and moves to the bottom of the list, and it keeps going on and on as long as clients keep requesting.
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by:jskfan
ID: 23691474
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by:bswinnerton
ID: 23694417
I don't know what you're talking about where you enter the ip addresses, but here is the snapshot you requested:



Picture-1.png
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by:jskfan
ID: 23695270
what about the snapshot for the IP addresses list, because it goes like a loop.
after the top IP in the list is given out it moves to the bottom then for previous second in the list will become the top and so on....

I know this provide load balancing when all the servers are on if one of them fail it doesn't.
But Round robin along with NLB I believe the load balancing and failover will be available.
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by:bswinnerton
ID: 23702319
I don't know about the snapshot that you are talking about. The IP addresses are in the A records (Like the first snapshot I posted).
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Author Comment

by:jskfan
ID: 23703116
Let's say you have 3 web servers
so in DNS you will create 3 records CNAME records.
www  10.0.0.10  server1.mycompany.com
www  10.0.0.11  server2.mycompany.com
www  10.0.0.12  server3.mycompany.com

and you check the check box Enable Round Robin
at the registrar you resgister mycompany.com and you will get for instance IP 69.69.69.69
let's say first public client Client1 opens a browse and enter www.mycompany.com the registrar will route the request to 69.69.69.69 (our external IP in the firwall), the firwalll will have a NAT that translate 69.69.69.69 to our internal DNS for instance 10.0.0.1.
Now at our DNS  level, how will Round Robin know just about the 3 records of the web servers and not about the rest of records that can be on the forward zone?
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by:bswinnerton
ID: 23714664
I'm confused as to what you're asking.

Are all of your webservers behind your firewall? If so, wouldn't you just enable round robin and then from there on make the same records?

e.g.

www 10.0.0.10
www 10.0.0.11
www 10.0.0.12
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Author Comment

by:jskfan
ID: 23717398
in the DNS  you have many records and you also put the following records
www 10.0.0.10
www 10.0.0.11
www 10.0.0.12

when you enable round robin,  how does it know that it should go through only the 3 records you mentioned. The bottom line is I want to understand how round robin knows which records in DNS  to take into consideration and which not.
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by:omarfarid
ID: 23724896
when a dns server has multiple ips for the same FQDN, it rotates the ips while replying to different queries. this means it sends all ips in the reply but keep shifting which ip is at the top of the list of ips. clients usually pick the ip on the top of the list received as an answer. This server behavior in rotating ips is round robin
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by:jskfan
ID: 23726863
so when you enable Round Robin, it will see by itself the records with the same FQDN and will rotate between them. No extra configuration just enable Round Robin?
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by:omarfarid
omarfarid earned 920 total points
ID: 23729832
Yes. you may try it from time to time and you will see the ips are rotated in the reply
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by:omarfarid
ID: 23729864
here output from my pc

C:\> nslookup www.google.com
Server:  dns.mydomain.com
Address:  10.0.0.10

Non-authoritative answer:
Name:    www.l.google.com
Addresses:  209.85.229.147, 209.85.229.99, 209.85.229.103, 209.85.229.104
Aliases:  www.google.com

C:\> nslookup www.google.com
Server:  dns.mydomain.com
Address:  10.0.0.10

Non-authoritative answer:
Name:    www.l.google.com
Addresses:  209.85.229.99, 209.85.229.103, 209.85.229.104, 209.85.229.147
Aliases:  www.google.com

C:\> nslookup www.google.com
Server:  dns.mydomain.com
Address:  10.0.0.10

Non-authoritative answer:
Name:    www.l.google.com
Addresses:  209.85.229.103, 209.85.229.104, 209.85.229.147, 209.85.229.99
Aliases:  www.google.com
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