The Samba AD DNS Back Ends

Revision as of 15:56, 29 December 2014 by Remsnet (talk | contribs) (Debian / Ubuntu + clones - Build New ISC Bind 9.8 / 9.9 / 9.10)

Which DNS backend should I choose?

You should choose the DNS backend based on the requirements of your network or existing DNS installations.

The internal DNS is a new implementation, that allows you to quickly and easily setup the DNS backend that is required for every AD installation. No further work is required to set it up. Currently it covers the important and required parts for AD.

If you already having BIND running, plan complex DNS setups or you require special functions (zone transfers only from defined hosts, etc.) that are currently not supported by the internal DNS, BIND should be the preferred backend.

Your choice of a DNS backend during provisioning/upgrading is not final. If you find that your choice doesn't fit your requirements, you can flip over and change the DNS backend.

Internal DNS

The internal DNS server is built into Samba and uses AD as backend. Also it is the default DNS solution when you provision/upgrade a Samba AD controller.


Configuration

If you chose the internal server as DNS backend for your environment, there are two options that can be added to your smb.conf to control the behaviour of DNS at this point:

# Don't allow any updates | allow unsigned updates | only allow signed updates
allow dns updates = False | nonsecure | signed

# If recursive queries = yes is set, the following is also needed
dns forwarder = <ip addr of external dns server>


Limitations / Known issues

  • The internal server is not a caching resolver.
  • The samba_dnsupdate command produces warnings when used with signed updates. We're currently investigating a fix for the warnings, but the updates actually succeed. Client systems like samba3 or Win7 work fine.
  • Currently, recursive queries are not possible without using a forwarder
  • Negative replies do not come with an authority record (not required by RFC, but Windows seems to like that)
  • Shared-key TSIG is not implemented
  • Stub zones are not implemented
  • Zone axfr is not allowed from internal samba DNS


Tests

Run during make test

TDB_NO_FSYNC=1 make test TESTS=samba.tests.dns

Run against external servers (Windows or BIND)

SERVER_IP=<dns server ip> SERVER=<dns server name> REALM=<dns server domain name part> PYTHONPATH=`pwd`/bin/python ./source4/scripting/bin/subunitrun samba.tests.dns




BIND DLZ plug-in (for BIND 9.8 and 9.9)

BIND can be setup to provide DNS resolving for zones managed in AD. They are accessable from BIND through the DLZ (dynamically loadable zones) plug-in. Please note that BIND server must run on the same machine as the Samba AD DC.


Installation / Setup

See the Bind as DNS backend HowTo for a detailed instruction.




Troubleshooting

Fix DNS dynamic updates with updated Samba versions

If you are running Samba 4.0.7 or later the bug https://bugzilla.samba.org/show_bug.cgi?id=9559 is already fixed. But if your samba was updated from old releases and it´s not a fresh installation you may have problems with dynamic DNS updates with Windows XP sp3 and Windows 7.

To fix the problem you need to follow this steps:

  • first of all, update your samba version if it is not the latest.
  • you may want to do a kinit to avoid samba-tool asking you for a password
kinit administrator

Search for all the registry entries that contain the broken records using:

samba-tool dns query SERVER DOMAIN @ ALL

You´ll find registries like this:

Name=WORKSTATION, Records=0, Children=0

For every registry entry found like the one above you´ll need to issue the following commands

/usr/local/samba/bin/samba-tool dns add SERVER DOMAIN WORKSTATION A IP -k yes
/usr/local/samba/bin/samba-tool dns delete SERVER DOMAIN WORKSTATION A IP -k yes

On windows workstations you can run

ipconfig /registerdns

And dynamic updates should work ok.



using ISC BIND backend with secured / signed dns updates

In the default configuration of Distributed ISC Bind in many Distributions you will find that the secured updates do not work with Samba 4. You will receive errors in /var/log/messages indicating update '<name of client>' denied i.e. This is because the rpm/deb/pkg has been compiled with the 'disable-isc-spnego' flag. In order to fix this you will need to recompile/rebuild the distribution rpm / deb / pkg .


common Bind9 Compile flags for BIND DLZ for bind 9.9

Samba4 and up require for BIND DLZ at least --with-dlz-ldap , --with-dlz-filesystem=yes,

Common used configure flags for BIND9.8.6 and up :

CONFIGURE_OPTIONS="\
...
--with-openssl \
--enable-threads \
--with-gssapi=yes \
--with-libtool \
--with-libxml2 \
--with-dlopen=yes \
--with-dlz-mysql \
--with-dlz-bdb \
--with-dlz-ldap \
--with-dlz-filesystem=yes \
--with-dlz-bdb=yes \
--enable-filter-aaaa \
--enable-rrl \
--with-ecdsa \
--enable-threads \
--with-idnlib='-L/usr/lib -R/usr/lib -lidn -lidn2' \
...

The parameters for "-L" "-R" can differ from Distribution needs.

... we ask herein  i386 / x64_64 and  Child Distribution Maintainers Members to update the package specs 
for Bind 9.8.5 and up to cover this for Samba4 in permanent.


RHEL / CENTOS / FC + clones - ReBuild Distrubuted ISC Bind RPM

First make sure you have your RPM build environment setup and then install the source rpm for bind. The instructions that follow are . For CENTOS 6.4 with 9.8.2-0.17.rc1.el6_4.6 being the latest version at the time of writing:

 rpm -i http://vault.centos.org/6.4/updates/Source/SPackages/bind-9.8.2-0.17.rc1.el6_4.6.src.rpm

Then locate and edit SPEC file, if your rpm build directory is ~/rpmbuild then it will be ~/rpmbuild/SPECS/bind.spec

now locate and remove the line that reads

 --disable-isc-spnego

On the example rpm provided it is line 361

now recompile your rpm

 rpmbuild -bb ~/rpmbuild/SPECS/bind.spec

Once finished you should find the replacement rpms in the RPMS/{arch} path of your build root. Replace {arch} with the relevant architecture of your machine (e.g. x86_64 or i686). Install them over the top of your existing rpms and updates should all be working again. Remember if you update with yum it may replace your copy of bind so you will either want to exclude bind* in your yum configuration or use priorities and add these rpms to a local repository.


OpenSuSE using ISC BIND backend

In the default configuration of Bind in the OpenSuSE distribution you will find that the secured updates do not work with Samba 4.1 and up . In order to fix this you will need to recompile the https://build.opensuse.org/package/show/openSUSE:Factory/bind .

User:Remsnet Published  https://github.com/remsnet/OpenSuSE-Samba-DC/blob/master/bind-9.9.4-P1.spec
 with Build Instructions at https://github.com/remsnet/OpenSuSE-Samba-DC/blob/master/Samba4-DC-DLZ.Readme

RHEL/CENTOS/FC + clones - RPM Build New ISC Bind 9.9 / 9.10

Benjamin Kraft publishes on his [1]  Bind9 Security Fixes Page.
Cleanly Patching Bind9 has almost been a task for experts ...
User:Remsnet Published https://github.com/remsnet/CentOS-Bind-DLZ SPEC File for SRPMS to Build a Clean and updated Bind9 with DLZ .


Debian / Ubuntu + clones - Build New ISC Bind 9.8 / 9.9 / 9.10

While following the official Samba4 HOWTO I found out that  bind would not start
giving me the following error (taken from my syslog):
Loading ‘AD DNS Zone’ using driver dlopen
unsupported DLZ database driver ‘dlopen’.  AD DNS Zone not loaded.

If you want some technical background as to what dlopen is read this blog post, but in short, Samba4 needs some features only available in Bind 9.8 and above. If you are getting the error I described above, you either have an earlier version or your binary version of Bind 9.8 or above was not compiled with support for dlz drivers.

To fix it I backported Bind9 from SID. This was the first time I ever did such a thing so I am no expert… if you know a better way to accomplish this please leave a comment.

Note: whenever Bing 9.8 gets backported it will become much easier to install, you will only have to follow the steps described here. For now, follow the instructions below. Let’s remove the old version of bind first:

sudo apt-get remove bind9

Install required packages:

sudo apt-get install devscripts build-essential libkrb5-dev debhelper libssl-dev libtool bison libdb-dev libldap2-dev libxml2-dev libpcap2-dev hardening-wrapper libgeoip-dev dpkg-dev

Download bind9 .dsc file (check here for the latest link to the .dsc file):

mkdir bind9 cd bind9 dget -x http://ftp.de.debian.org/debian/pool/main/b/bind9/bind9_9.8.1.dfsg-1.dsc

Now unpack bind:

tar xvzf bind9_9.8.1.dfsg.orig.tar.gz cd bind9_9.8.1.dfsg/

Note: I will skip applying the .diff file from sid. When I tried applying it the source would not compile and, most importantly, it stopped recognising the –with-dlz-dlopen parameter which is the reason why I had to do this in the first place. Configure and then compile Bind9 source code:

fakeroot ./configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info \

        --sysconfdir=/etc/bind --localstatedir=/var --enable-threads --enable-largefile --with-libtool \
        --enable-shared --enable-static --with-openssl=/usr --with-gssapi=/usr --with-gnu-ld \
        --with-dlz-postgres=no --with-dlz-mysql=no --with-dlz-bdb=yes --with-dlz-filesystem=yes \
        --with-dlz-ldap=yes  --with-dlz-stub=yes --with-dlz-dlopen=yes \
         --with-geoip=/usr --enable-ipv6 CFLAGS=-fno-strict-aliasing 

If you are using bind9 9.8.1 you may find a compilation error which can be fixed with the patch described here. You can apply the patch manually, all you have to do is edit the file contrib/dlz/drivers/sdlz_helper.c and remove the “#ifdef DLZ” line and the “#endif” line at the end of the file. Now let’s compile and install bind9:

make install

Last step, we need to manually create the /var/cache/bind directory:

sudo mkdir /var/cache/bind

Start the service:

sudo /etc/init.d bind9 start

Hopefully, bind9 will start just fine.

Congratulations, bind9 should be working now. If you are following the Samba4 HOWTO like I was, make sure you run the provisioning steps again with bind9 running.