Reducing DNS lookups

Brendan Kearney bpk678 at
Tue Feb 21 13:22:27 CET 2017

On 02/21/2017 07:10 AM, David Hartburn wrote:
> Hi,
> For our LDAP queries, we have specified the forest DNS name as the 
> LDAP server, so that we achieve via DNS a random distribution of 
> queries against our AD servers. Previously we had hammered the first 
> server on the list.
> This has kept our AD guys happy, but we have noticed that at busy 
> times our FR servers are doing over 100 DNS queries per second, for 
> the same thing.
> I can not spot anything in the FreeRADIUS config files, but is there 
> any way to reduce the number of DNS lookups? We are running 3.0.12 on 
> RHEL7.
> Outside of FreeRADIUS, we could either make sure each server has a 
> different /etc/hosts file, which is not ideal, or implementing local 
> DNS caching seems to be the more sensible way to go. Are there any 
> other alternatives other people are using?
> Yours
> Dave Hartburn
> -
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i have wondered if using SRV records would be feasible.  the SSSD 
project has a nifty config option that allows you to specify "_srv_" as 
a value in a comma separated string, to indicate the use of the 
_ldap._tcp.domain.tld and _kerberos._udp.domain.tld SRV records.  the 
SRV record can be set with weight and priority to steer load, and is a 
round-robin style load balancing mechanism. in addition, you can also 
specify specific ldap URIs or kerberos servers in the config option for 
fallback to specific servers.

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