RE: [load balancing] DNS Order

From: Tim Maestas <>
Date: Sat Feb 19 2005 - 23:42:40 EST

While that's true for A records, that is not necessarily true for
delegated domains. Modern versions of Bind will internally track round
trip times to nameservers for a given domain and will tend to favor
servers with better round trip times for queries. However, since it has
to periodically check all of the nameservers to see if query time has
deteriated or improved, you will see queries to all nameservers, just more
to the one that performs better.


On Sat, 19 Feb 2005, Mike Adams wrote:

> Bind uses simple round robin to determine which address to give out if there
> are multiple NS or A records for a single entry.
> -----Original Message-----
> From: []On Behalf Of Claret
> Carvalho
> Sent: Saturday, February 19, 2005 10:57 AM
> To:
> Subject: [load balancing] DNS Order
> Hi there,
> Just wanted to poll the GSLB experts on a DNS related question.
> In our enterprise, we have local DNS servers that pass the resolution
> queries for any load balanced domains to the gslb (GSS, 3DNS etc) devices
> and just wanted to ask whether Bind uses any particular algorithm in
> selecting which gslb device to handle the query. Do the local DNS servers
> choose the closest gslb device to make the query based on some initial Round
> trip time poll and how long is that state generally maintained if so or does
> it basically select the first DNS server in the list or does it just round
> robin this and any subsequent queries for the same record ?
> For instance, if i have the following on my local DNS Bind v8 configuration
> where a domain is handled by multiple geographic gslb devices in different
> continents,
> NS (london appliance )
> (new york appliance)
> Client A -------------------------------> Local
> DNS -------------------------> Would this query go to london gslb or nyc
> gslb ?
> making a request for (location: London)
> (location: London)
> I know that this behaviour is different from entries in /etc/resolver.conf
> or dns server order on the Unix or Win clients where the first DNS server
> entered is the primary server always. In our environment, while we have seen
> most DNS queries go to the Ldn device, some do trickle down to the nyc, so
> just trying to understand if it has any known/fixed method that it uses.
> Thanks for your replies,
> Claret

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Received on Sun Feb 20 00:47:09 2005

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