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Re: [Samba] DNS issues after upgrade




Hi Rowland / Denis,

Thanks for your quick reply. Find below smb.conf and named.conf for your reference.

Few things I wish to clarify here.

1. We have installed the samba on CentOS 7.4 not on Debian OS. As, packages from repositories are of version 4.3 and 4.4, we have used sources, compiled & installed the package.

2. named.log had an entry "DNSKEY (.) could not be obtained, Time Out". But named-checkconf did not return any errors.

3. We did run dbcheck and dbcheck --cross-ncs. It threw some erros. We fixed it. Yet, DNS could not resolve.

We are now simulating the production environment in our testing virtual machines. We are trying to reproduce the error to check really what went wrong.

We request for your guidance in getting to the bottom of the issue and resolving it. Keeping the security requirements in mind, we have to upgrade to 4.7 and above as early as possible.

Look forward for your guidance.

_*smb.conf*_

# Global parameters
[global]
    netbios name = DC1
    realm = ***********.COM
    server services = s3fs, rpc, nbt, wrepl, ldap, cldap, kdc, drepl, winbindd, ntp_signd, kcc, dnsupdate
    workgroup = *********
    server role = active directory domain controller
    idmap_ldb:use rfc2307 = yes
    ldap server require strong auth = No
#eventlog list = Application System Security SyslogLinux
        eventlog list = Application, Security
        #Log Level
        log level = 3
        log file = /var/log/samba/pdc.%T.log

[netlogon]
    path = /usr/local/samba/var/locks/sysvol/**********.com/scripts
    read only = No

[sysvol]
    path = /usr/local/samba/var/locks/sysvol
    read only = No

[shares]
        comment = For all Users
        path = /home/shares
        read only = No
        writable = Yes

**_**_

_*named.conf*_

// named.conf
//
// Provided by Red Hat bind package to configure the ISC BIND named(8) DNS
// server as a caching only nameserver (as a localhost DNS resolver only).
//
// See /usr/share/doc/bind*/sample/ for example named configuration files.
//
// See the BIND Administrator's Reference Manual (ARM) for details about the
// configuration located in /usr/share/doc/bind-{version}/Bv9ARM.html

options {
        listen-on port 53 { any; };
        listen-on-v6 port 53 { none; };
        directory       "/var/named";
        dump-file       "/var/named/data/cache_dump.db";
        statistics-file "/var/named/data/named_stats.txt";
        memstatistics-file "/var/named/data/named_mem_stats.txt";
        allow-query     { any; };

        /*
         - If you are building an AUTHORITATIVE DNS server, do NOT enable recursion.          - If you are building a RECURSIVE (caching) DNS server, you need to enable
           recursion.
         - If your recursive DNS server has a public IP address, you MUST enable access            control to limit queries to your legitimate users. Failing to do so will            cause your server to become part of large scale DNS amplification
           attacks. Implementing BCP38 within your network would greatly
           reduce such attack surface
        */
        recursion yes;
        forwarders {
                172.##.###.10; //***** internal DNS 1
                172.##.###.90; //****** internal DNS 2
        };
        dnssec-enable yes;
        dnssec-validation yes;

        /* Path to ISC DLV key */
        bindkeys-file "/etc/named.iscdlv.key";

        managed-keys-directory "/var/named/dynamic";

        pid-file "/run/named/named.pid";
        session-keyfile "/run/named/session.key";
        tkey-gssapi-keytab "/usr/local/samba/private/dns.keytab";
};

logging {
        channel default_debug {
                file "data/named.run";
                severity dynamic;
        };
};

zone "." IN {
        type hint;
        file "named.ca";
};

include "/etc/named.rfc1912.zones";
include "/etc/named.root.key";
include "/usr/local/samba/private/named.conf";


--

Thanks & Regards,


Anantha Raghava

eXzaTech Consulting And Services Pvt. Ltd.

Ph: +91-9538849179, E-mail: raghav@xxxxxxxxxxxxxxxxxxxxxx <mailto:raghav@xxxxxxxxxxxxxxxxxxxxxx>

URL: http://www.exzatechconsulting.com <http://www.exzatechconsulting.com/>



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On 22/01/18 3:25 PM, Denis Cardon wrote:
Hi Anantha,

The upgrade from 4.6.5 broke all the servers. Although the services were
running and there is no error message, DNS resolution failed. Even from
inside the domain controllers, DNS queries failed.

Samba Version 4.7.1 and Named Version 9.9.4. The same issue happened
with samba version 4.7.3 and 4.7.4

We had to revert back to 4.6.5 to bring the servers back online. Now I
have few questions:

1. On the the DCs, we stopped both samba-ad-dc and named services,  just
compiled samba 4.7.1 & installed without making any changes to the
folders or the files. On three of our 4 servers it worked without any
issues. On the fourth server which owned all FSMO roles, although both
samba-ad-dc and named services were running (no errors were thrown), DNS
could not respond to any queries. For some time, two of the servers were
working and they also stopped resolving any names. Whether database
replication faulted the other working servers as well, we are not having
clarity.

2. Is there any specific procedure to be followed to upgrade? As
mentioned above, we have just compiled the latest version from sources
and installed on 4.6.5. The process that worked on 3 servers failed &
broke the DNS on 4th server that owned all FSMO roles. Should we have
transferred the FSMO roles to other working servers before upgrade process?

3. Since samba 4.7.x is a multi-process server, is there any DB locking
issue, that is stopping named process from reading DB?

Like you are pointing out, 4.7 gets a performance boost with more multi-processing. However until 4.8 gets out, you may get issues with memory consumption if you have too many LDAP or RPC connections simultaneously. But it can be mitigated (see previous post on the subject). But it didn't trigger any issues on DNS side for us.

By the way, in any case you should go with 4.7.4 and not 4.7.1.

4. In named logs, we say that it was unable to obtain the DNAKEY (.) and
it was timing out. But this error was shown even before the upgrade. It
turned out be a warning that can be safely ignored.

5. We switched back from BIND9_DLZ DNS Back end to SAMBA_INTERNAL DNS
Back end, the same issue continued. DNS failed to respond to any
queries. Even internally with in DCs, ping the self could not resolve
name & returned error.

The fact that internal DNS was not working would rule out a problem with your Bind-DLZ configuration...

Did you run samba-tool dbcheck --cross-ncs after upgrade? There has been some issues on 4.6 to 4.7 upgrades with group membership, but I never had an issue on the DNS partitions though. Do you have some Windows AD join to you Samba domain?

Like Rowland was saying, could you post your smb.conf file too see if there is anything weird in there.

By the way, unless you have specific requirements, you should stick to pre-compiled deb packages. There are many options, from Samba Plus packages with direct support from SerNet, the package from LPH van Belle, or ours at TIS. It would help to rule out any build/compilation issues.

Cheers,

Denis




6. Finally, when we downgraded, everything started working properly. on
the version 4.7.4, we just compiled 4.6.5 and installed. Just reversed
the upgrade process. It started working. All servers came back to
normal. This is really surprising. Since it is a production setup that
is serving the entire India, we just reverted all servers back to 4.6.5.

7. While we observed some network latency, it is not the culprit for
stopping of response to DNS queries that stopped the entire 9000 users
from logging in.

Now we are simulating the same error in our lab setup to figure out the
root cause for the issue, before upgrading the production servers.

I seek your expert guidance and help to get to the root cause of the
problem.



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