[Dovecot] dovecot: auth(default): LDAP: ldap_result() failed: Can't contact LDAP server

[Rolf E. Sonneveld]

Hi,

I'm new to the list; excuse me if this has been asked recently/before.

running:
# dovecot --version
1.0.8

Output of dovecot -n:

base_dir: /var/run/dovecot
protocols: none
ssl_disable: yes
login_dir: /var/run/dovecot/login
login_executable: /usr/local/dovecot/libexec/dovecot/imap-login
auth default:
  verbose: yes
  debug: yes
  debug_passwords: yes
  passdb:
    driver: ldap
    args: /usr/local/dovecot/etc/dovecot-ldap.conf
  userdb:
    driver: ldap
    args: /usr/local/dovecot/etc/dovecot-ldap.conf
  socket:
    type: listen
    client:
      path: /usr/local/postfix/spool/private/auth
      mode: 432
      user: postfix
      group: postfix
    master:
      path: /var/run/dovecot-auth-master
      mode: 438

Using dovecot only for the purpose of providing SMTP AUTH service for 
Postfix, using Active Directory (AD) as authentication source. As you 
can see from the config, connectivity between Dovecot and AD is 
implemented using LDAP.

Contents of /usr/local/dovecot/etc/dovecot-ldap.conf (some site-specific 
info masqueraded):

auth_bind = yes
pass_filter = (sAMAccountName=%u)
hosts = AD1.domain.com:3268 AD2.domain.com:3268
dn = CN=Service Account Postfix,OU=Services,DC=domain,DC=com
dnpass = secret
ldap_version = 3
base = DC=domain,DC=com
scope = subtree

Now, this works fine and authentication via SMTP AUTH + Dovecot works 
perfect. Yet, every 15 minutes I get the following warning in the syslog 
logfile:

Dec 24 07:20:00 hostname dovecot: auth(default): LDAP: ldap_result() 
failed: Can't contact LDAP server
Dec 24 07:35:01 hostname dovecot: auth(default): LDAP: ldap_result() 
failed: Can't contact LDAP server
Dec 24 07:50:01 hostname dovecot: auth(default): LDAP: ldap_result() 
failed: Can't contact LDAP server
Dec 24 08:05:02 hostname dovecot: auth(default): LDAP: ldap_result() 
failed: Can't contact LDAP server
Dec 24 08:20:02 hostname dovecot: auth(default): LDAP: ldap_result() 
failed: Can't contact LDAP server
Dec 24 08:35:03 hostname dovecot: auth(default): LDAP: ldap_result() 
failed: Can't contact LDAP server

I've looked through the archives and it seems that this problem is 
caused by the fact that Dovecot (using the OpenLDAP client libraries?) 
keeps the LDAP connection open; after (in our case) 15 minutes Active 
Directory closes the connection and Dovecot signals this in the syslog 
(and presumably automatically will create a new connection to AD).

I'm pretty sure that the OpenLDAP client libraries provide options to 
use a client-side timeout for LDAP connections. My questions are:

    * is there a reason that Dovecot wants to keep the LDAP connection open?
    * Will the new V1.1 version have a config parameter to set the LDAP
      client timeout or a default timeout value to close the connection?
    * If there's no 'fix' foreseen for V1.1, I'd like to file a request
      to add such a parameter. How can I file such a request?


The warning is annoying; the sysadmin will create a filter, to filter 
the warning out from the syslog, but I'm afraid that if there's a real 
problem with authentication, that will be filtered too and the real 
problem is not noticed, before users start to complain.

/rolf