redundant load balancing and mschap

McNutt, Justin M. McNuttJ at
Sat Aug 25 00:53:18 CEST 2012

The underlying problem is that I have four production RADIUS servers that all seem to choose the same domain controller, which is not only a lot of load, but it's a bad idea in terms of fault tolerance.

I may try just making each server "choose" a separate DC as its default, for starters, which would get me most of the way there.  The wireless controllers that authenticate against the RADIUS servers *themselves* round-robin among the RADIUS servers, so if one of them - or even two of them - were talking to a DC that is down, a given user's machine is likely to re-attempt authentication and succeed eventually.  We'd hear a lot of complaints that "getting on wireless is slow" but things would *work*.

Anyway, thanks for the insight.  I'll keep banging on it.  If I get an elegant - or at least *stable* - configuration, I'll post something about it here.


-----Original Message-----
From: at [ at] On Behalf Of Phil Mayers
Sent: Friday, August 24, 2012 4:23 PM
To: freeradius-users at
Subject: Re: redundant load balancing and mschap

On 08/24/2012 08:11 PM, McNutt, Justin M. wrote:
> Grrr...
> This is probably a Samba issue - a known one? - but I can't seem to 
> get AD authentications to hit multiple DCs.  Everything goes to the 
> one

This is indeed a Samba issue, and unfortunately a hard one to fix.

ntlm_auth doesn't talk over the network - rather, it talks over a Unix socket to winbind. Winbind maintains a *single* open session to a DC, and sends all the domain RPCs down this pipe.

Winbind discovers the DC from the AD subnet/site queries and builds an app-specific kerberos config that will show you this - see /var/lib/samba/smb_krb5/krb5.conf.<DOMNAME>

If you want to force connections to separate domain controllers, you'll need separate smbd/winbindd instances running, with their own unix sockets and smb.conf setups. This will probably be hard, and fragile.

My advice - don't, unless you really really need to.
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