samba - Jan 2012 - Could not write response[27830:AUTH_CRAP] to client: Broken pipe

Hello,

We're using FreeRADIUS and winbind to authenticate access to our wireless
network. The problem we're experiencing
is that the secure channel between the wbind daemon and the DC appears to be
unstable. The outages last for about
30 seconds and coincide with a series of "...Broken pipe" messages in
the log.winbindd file (see below).  Is this
a samba fault or an DC issue, e.g. the DC has an insufficient number of threads
to handle the number of NTLM
authentication requests? The problem is related to the rate of authentication
requests handled by the RADIUS
server.

Any help in resolving this problem would be appreciated.

Thanks,

Chris

========================================================
1. Active Directory 

Domain controllers MS 2008 R2 and MS 2003 SP2
Forest consists of parent domain and a child domain
RADIUS server trust account is in the parent domain

2. RADIUS server software
 
CentOS Linux release 6.0 (Final)
Linux 2.6.32-71.29.1.el6.x86_64 #1 SMP Mon Jun 27 19:49:27 BST 2011 x86_64
x86_64 x86_64 GNU/Linux
samba3-3.5.12-44.el6.x86_64
samba3-client-3.5.12-44.el6.x86_64
samba3-winbind-3.5.12-44.el6.x86_64
libwbclient0-3.5.12-44.el6.x86_64

3. Smb.conf
[global]
        workgroup = X
        realm = Y
        server string = Z
        security = ADS
        log level = 3
        log file = /var/log/samba/log.%m
        max log size = 10000
        machine password timeout = 0
        idmap uid = 16777216-33554431
        idmap gid = 16777216-33554431
        template shell = /bin/bash
        winbind separator = +
        winbind reconnect delay = 5
        winbind enum users = Yes
        winbind enum groups = Yes
        winbind use default domain = Yes
        cups options = raw


4. log.wibnindd

[2012/01/09 09:11:58.130332,  3]
winbindd/winbindd_misc.c:352(winbindd_interface_version)
  [27855]: request interface version
[2012/01/09 09:11:58.130409,  3]
winbindd/winbindd_misc.c:385(winbindd_priv_pipe_dir)
  [27855]: request location of privileged pipe
[2012/01/09 09:11:58.130561,  3]
winbindd/winbindd_pam.c:1838(winbindd_pam_auth_crap)
  [27855]: pam auth crap domain: [X] user: Y
[2012/01/09 09:11:58.189225,  2]
winbindd/winbindd.c:710(winbind_client_response_written)
  Could not write response[27824:AUTH_CRAP] to client: Broken pipe
[2012/01/09 09:11:58.191401,  2]
winbindd/winbindd.c:710(winbind_client_response_written)
  Could not write response[27825:AUTH_CRAP] to client: Broken pipe
[2012/01/09 09:11:58.193051,  2]
winbindd/winbindd.c:710(winbind_client_response_written)
  Could not write response[27826:AUTH_CRAP] to client: Broken pipe
[2012/01/09 09:11:58.194817,  2]
winbindd/winbindd.c:710(winbind_client_response_written)
  Could not write response[27828:AUTH_CRAP] to client: Broken pipe
[2012/01/09 09:11:58.196244,  2]
winbindd/winbindd.c:710(winbind_client_response_written)
  Could not write response[27829:AUTH_CRAP] to client: Broken pipe
[2012/01/09 09:11:58.197875,  2]
winbindd/winbindd.c:710(winbind_client_response_written)
  Could not write response[27830:AUTH_CRAP] to client: Broken pipe
[2012/01/09 09:11:58.919829,  3]
winbindd/winbindd_misc.c:352(winbindd_interface_version)
  [27857]: request interface version
[2012/01/09 09:11:58.919904,  3]
winbindd/winbindd_misc.c:385(winbindd_priv_pipe_dir)
  [27857]: request location of privileged pipe
[2012/01/09 09:11:58.920040,  3]
winbindd/winbindd_pam.c:1838(winbindd_pam_auth_crap)
  [27857]: pam auth crap domain: [X] user: Y
[2012/01/09 09:11:59.980616,  3]
winbindd/winbindd_misc.c:352(winbindd_interface_version)
  [27858]: request interface version