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Linux round Robin DNS

Posted on 2007-11-29
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Last Modified: 2010-05-18
I am confused on Linux DNS Round Robin.

If I have a hostname with several different ips , this seems to work correctly as each time I ping I get a different ip to that same hostname. My guess is that the ttl is set very low for this to work. ( I did not build this)

My confusion is probalby that I am thinkng to windows on this . However, if I do the same setup in Wndows. the client resovler cache will cache the first ip it resolves and then use that until cahce times out. So, this kind of defeats the notion of round robin DNS. I can turn the client cache off but now that increases traffic to DNS server. Also will ignore TTL , unless you play with registry...

Does Linux not have a client resolver and that is why this is not an issue????
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Question by:andrew_89
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WizRd-Linux earned 500 total points
ID: 20379829
linux does it is called nscd.  Check if the service is started, however I believe that nscd adheres to the TTL on DNS records.
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by:omarfarid
ID: 20380195
Hi,

WizRd-Linux is correct in that linux has nscd process that caches dns resolutions.

One thing I want to say about dns round robin. The dns server always reply to quires with a list of IPs for the domain name, but it rotate it thus it is round robin. The client receives the list and mostly use the first ip in the list and continue to use that ip address until ttl expires or the ip does not response.

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by:andrew_89
ID: 20381195
om so this is not the saem behaviour as windows client DNS cache. AS even when ttl expires the client will consult the cache first and will not go query a DNS server. This causes it to use the same ip and is not true DNS round robin.

Unless of course you disable the client cache.
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