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[freebsd-src/fkvm-freebsd.git] / contrib / bind9 / FAQ

Frequently Asked Questions about BIND 9

Copyright © 2004-2007 Internet Systems Consortium, Inc. ("ISC")

Copyright © 2000-2003 Internet Software Consortium.

-----------------------------------------------------------------------

1. Compilation and Installation Questions

Q: I'm trying to compile BIND 9, and "make" is failing due to files not
   being found. Why?

A: Using a parallel or distributed "make" to build BIND 9 is not
   supported, and doesn't work. If you are using one of these, use normal
   make or gmake instead.

Q: Isn't "make install" supposed to generate a default named.conf?

A: Short Answer: No.

   Long Answer: There really isn't a default configuration which fits any
   site perfectly. There are lots of decisions that need to be made and
   there is no consensus on what the defaults should be. For example
   FreeBSD uses /etc/namedb as the location where the configuration files
   for named are stored. Others use /var/named.

   What addresses to listen on? For a laptop on the move a lot you may
   only want to listen on the loop back interfaces.

   Who do you offer recursive service to? Is there are firewall to
   consider? If so is it stateless or stateful. Are you directly on the
   Internet? Are you on a private network? Are you on a NAT'd network? The
   answers to all these questions change how you configure even a caching
   name server.

2. Configuration and Setup Questions

Q: Why does named log the warning message "no TTL specified - using SOA
   MINTTL instead"?

A: Your zone file is illegal according to RFC1035. It must either have a
   line like:

   $TTL 86400

   at the beginning, or the first record in it must have a TTL field, like
   the "84600" in this example:

   example.com. 86400 IN SOA ns hostmaster ( 1 3600 1800 1814400 3600 )

Q: Why do I get errors like "dns_zone_load: zone foo/IN: loading master
   file bar: ran out of space"?

A: This is often caused by TXT records with missing close quotes. Check
   that all TXT records containing quoted strings have both open and close
   quotes.

Q: How do I restrict people from looking up the server version?

A: Put a "version" option containing something other than the real version
   in the "options" section of named.conf. Note doing this will not
   prevent attacks and may impede people trying to diagnose problems with
   your server. Also it is possible to "fingerprint" nameservers to
   determine their version.

Q: How do I restrict only remote users from looking up the server version?

A: The following view statement will intercept lookups as the internal
   view that holds the version information will be matched last. The
   caveats of the previous answer still apply, of course.

   view "chaos" chaos {
           match-clients { <those to be refused>; };
           allow-query { none; };
           zone "." {
                   type hint;
                   file "/dev/null";  // or any empty file
           };
   };

Q: What do "no source of entropy found" or "could not open entropy source
   foo" mean?

A: The server requires a source of entropy to perform certain operations,
   mostly DNSSEC related. These messages indicate that you have no source
   of entropy. On systems with /dev/random or an equivalent, it is used by
   default. A source of entropy can also be defined using the
   random-device option in named.conf.

Q: I'm trying to use TSIG to authenticate dynamic updates or zone
   transfers. I'm sure I have the keys set up correctly, but the server is
   rejecting the TSIG. Why?

A: This may be a clock skew problem. Check that the the clocks on the
   client and server are properly synchronised (e.g., using ntp).

Q: I see a log message like the following. Why?

   couldn't open pid file '/var/run/named.pid': Permission denied

A: You are most likely running named as a non-root user, and that user
   does not have permission to write in /var/run. The common ways of
   fixing this are to create a /var/run/named directory owned by the named
   user and set pid-file to "/var/run/named/named.pid", or set pid-file to
   "named.pid", which will put the file in the directory specified by the
   directory option (which, in this case, must be writable by the named
   user).

Q: I can query the nameserver from the nameserver but not from other
   machines. Why?

A: This is usually the result of the firewall configuration stopping the
   queries and / or the replies.

Q: How can I make a server a slave for both an internal and an external
   view at the same time? When I tried, both views on the slave were
   transferred from the same view on the master.

A: You will need to give the master and slave multiple IP addresses and
   use those to make sure you reach the correct view on the other machine.

   Master: 10.0.1.1 (internal), 10.0.1.2 (external, IP alias)
       internal:
           match-clients { !10.0.1.2; !10.0.1.4; 10.0.1/24; };
                   notify-source 10.0.1.1;
                   transfer-source 10.0.1.1;
                   query-source address 10.0.1.1;
       external:
           match-clients { any; };
           recursion no;   // don't offer recursion to the world
           notify-source 10.0.1.2;
           transfer-source 10.0.1.2;
           query-source address 10.0.1.2;

   Slave: 10.0.1.3 (internal), 10.0.1.4 (external, IP alias)
       internal:
           match-clients { !10.0.1.2; !10.0.1.4; 10.0.1/24; };
           notify-source 10.0.1.3;
           transfer-source 10.0.1.3;
           query-source address 10.0.1.3;
      external:
           match-clients { any; };
           recursion no;   // don't offer recursion to the world
           notify-source 10.0.1.4;
           transfer-source 10.0.1.4;
           query-source address 10.0.1.4;

   You put the external address on the alias so that all the other dns
   clients on these boxes see the internal view by default.

A: BIND 9.3 and later: Use TSIG to select the appropriate view.

   Master 10.0.1.1:
           key "external" {
                   algorithm hmac-md5;
                   secret "xxxxxxxx";
           };
           view "internal" {
                   match-clients { !key external; 10.0.1/24; };
                   ...
           };
           view "external" {
                   match-clients { key external; any; };
                   server 10.0.1.2 { keys external; };
                   recursion no;
                   ...
           };

   Slave 10.0.1.2:
           key "external" {
                   algorithm hmac-md5;
                   secret "xxxxxxxx";
           };
           view "internal" {
                   match-clients { !key external; 10.0.1/24; };
                   ...
           };
           view "external" {
                   match-clients { key external; any; };
                   server 10.0.1.1 { keys external; };
                   recursion no;
                   ...
           };

Q: I get error messages like "multiple RRs of singleton type" and "CNAME
   and other data" when transferring a zone. What does this mean?

A: These indicate a malformed master zone. You can identify the exact
   records involved by transferring the zone using dig then running
   named-checkzone on it.

   dig axfr example.com @master-server > tmp
   named-checkzone example.com tmp

   A CNAME record cannot exist with the same name as another record except
   for the DNSSEC records which prove its existence (NSEC).

   RFC 1034, Section 3.6.2: "If a CNAME RR is present at a node, no other
   data should be present; this ensures that the data for a canonical name
   and its aliases cannot be different. This rule also insures that a
   cached CNAME can be used without checking with an authoritative server
   for other RR types."

Q: I get error messages like "named.conf:99: unexpected end of input"
   where 99 is the last line of named.conf.

A: Some text editors (notepad and wordpad) fail to put a line title
   indication (e.g. CR/LF) on the last line of a text file. This can be
   fixed by "adding" a blank line to the end of the file. Named expects to
   see EOF immediately after EOL and treats text files where this is not
   met as truncated.

Q: How do I share a dynamic zone between multiple views?

A: You choose one view to be master and the second a slave and transfer
   the zone between views.

   Master 10.0.1.1:
           key "external" {
                   algorithm hmac-md5;
                   secret "xxxxxxxx";
           };

           key "mykey" {
                   algorithm hmac-md5;
                   secret "yyyyyyyy";
           };

           view "internal" {
                   match-clients { !key external; 10.0.1/24; };
                   server 10.0.1.1 {
                           /* Deliver notify messages to external view. */
                           keys { external; };
                   };
                   zone "example.com" {
                           type master;
                           file "internal/example.db";
                           allow-update { key mykey; };
                           notify-also { 10.0.1.1; };
                   };
           };

           view "external" {
                   match-clients { key external; any; };
                   zone "example.com" {
                           type slave;
                           file "external/example.db";
                           masters { 10.0.1.1; };
                           transfer-source { 10.0.1.1; };
                           // allow-update-forwarding { any; };
                           // allow-notify { ... };
                   };
           };

Q: I get a error message like "zone wireless.ietf56.ietf.org/IN: loading
   master file primaries/wireless.ietf56.ietf.org: no owner".

A: This error is produced when a line in the master file contains leading
   white space (tab/space) but the is no current record owner name to
   inherit the name from. Usually this is the result of putting white
   space before a comment, forgetting the "@" for the SOA record, or
   indenting the master file.

Q: Why are my logs in GMT (UTC).

A: You are running chrooted (-t) and have not supplied local timezone
   information in the chroot area.

   FreeBSD: /etc/localtime
   Solaris: /etc/TIMEZONE and /usr/share/lib/zoneinfo
   OSF: /etc/zoneinfo/localtime

   See also tzset(3) and zic(8).

Q: I get "rndc: connect failed: connection refused" when I try to run
   rndc.

A: This is usually a configuration error.

   First ensure that named is running and no errors are being reported at
   startup (/var/log/messages or equivalent). Running "named -g <usual
   arguments>" from a title can help at this point.

   Secondly ensure that named is configured to use rndc either by
   "rndc-confgen -a", rndc-confgen or manually. The Administrators
   Reference manual has details on how to do this.

   Old versions of rndc-confgen used localhost rather than 127.0.0.1 in /
   etc/rndc.conf for the default server. Update /etc/rndc.conf if
   necessary so that the default server listed in /etc/rndc.conf matches
   the addresses used in named.conf. "localhost" has two address
   (127.0.0.1 and ::1).

   If you use "rndc-confgen -a" and named is running with -t or -u ensure
   that /etc/rndc.conf has the correct ownership and that a copy is in the
   chroot area. You can do this by re-running "rndc-confgen -a" with
   appropriate -t and -u arguments.

Q: I get "transfer of 'example.net/IN' from 192.168.4.12#53: failed while
   receiving responses: permission denied" error messages.

A: These indicate a filesystem permission error preventing named creating
   / renaming the temporary file. These will usually also have other
   associated error messages like

   "dumping master file: sl/tmp-XXXX5il3sQ: open: permission denied"

   Named needs write permission on the directory containing the file.
   Named writes the new cache file to a temporary file then renames it to
   the name specified in named.conf to ensure that the contents are always
   complete. This is to prevent named loading a partial zone in the event
   of power failure or similar interrupting the write of the master file.

   Note file names are relative to the directory specified in options and
   any chroot directory ([<chroot dir>/][<options dir>]).

   If named is invoked as "named -t /chroot/DNS" with the following
   named.conf then "/chroot/DNS/var/named/sl" needs to be writable by the
   user named is running as.

   options {
           directory "/var/named";
   };

   zone "example.net" {
           type slave;
           file "sl/example.net";
           masters { 192.168.4.12; };
   };

Q: I want to forward all DNS queries from my caching nameserver to another
   server. But there are some domains which have to be served locally, via
   rbldnsd.

   How do I achieve this ?

A: options {
           forward only;
           forwarders { <ip.of.primary.nameserver>; };
   };

   zone "sbl-xbl.spamhaus.org" {
           type forward; forward only;
           forwarders { <ip.of.rbldns.server> port 530; };
   };

   zone "list.dsbl.org" {
           type forward; forward only;
           forwarders { <ip.of.rbldns.server> port 530; };
   };


Q: Can you help me understand how BIND 9 uses memory to store DNS zones?

   Some times it seems to take several times the amount of memory it needs
   to store the zone.

A: When reloading a zone named my have multiple copies of the zone in
   memory at one time. The zone it is serving and the one it is loading.
   If reloads are ultra fast it can have more still.

   e.g. Ones that are transferring out, the one that it is serving and the
   one that is loading.

   BIND 8 destroyed the zone before loading and also killed off outgoing
   transfers of the zone.

   The new strategy allows slaves to get copies of the new zone regardless
   of how often the master is loaded compared to the transfer time. The
   slave might skip some intermediate versions but the transfers will
   complete and it will keep reasonably in sync with the master.

   The new strategy also allows the master to recover from syntax and
   other errors in the master file as it still has an in-core copy of the
   old contents.

3. General Questions

Q: I keep getting log messages like the following. Why?

   Dec 4 23:47:59 client 10.0.0.1#1355: updating zone 'example.com/IN':
   update failed: 'RRset exists (value dependent)' prerequisite not
   satisfied (NXRRSET)

A: DNS updates allow the update request to test to see if certain
   conditions are met prior to proceeding with the update. The message
   above is saying that conditions were not met and the update is not
   proceeding. See doc/rfc/rfc2136.txt for more details on prerequisites.

Q: I keep getting log messages like the following. Why?

   Jun 21 12:00:00.000 client 10.0.0.1#1234: update denied

A: Someone is trying to update your DNS data using the RFC2136 Dynamic
   Update protocol. Windows 2000 machines have a habit of sending dynamic
   update requests to DNS servers without being specifically configured to
   do so. If the update requests are coming from a Windows 2000 machine,
   see http://support.microsoft.com/support/kb/articles/q246/8/04.asp for
   information about how to turn them off.

Q: When I do a "dig . ns", many of the A records for the root servers are
   missing. Why?

A: This is normal and harmless. It is a somewhat confusing side effect of
   the way BIND 9 does RFC2181 trust ranking and of the efforts BIND 9
   makes to avoid promoting glue into answers.

   When BIND 9 first starts up and primes its cache, it receives the root
   server addresses as additional data in an authoritative response from a
   root server, and these records are eligible for inclusion as additional
   data in responses. Subsequently it receives a subset of the root server
   addresses as additional data in a non-authoritative (referral) response
   from a root server. This causes the addresses to now be considered
   non-authoritative (glue) data, which is not eligible for inclusion in
   responses.

   The server does have a complete set of root server addresses cached at
   all times, it just may not include all of them as additional data,
   depending on whether they were last received as answers or as glue. You
   can always look up the addresses with explicit queries like "dig
   a.root-servers.net A".

Q: Why don't my zones reload when I do an "rndc reload" or SIGHUP?

A: A zone can be updated either by editing zone files and reloading the
   server or by dynamic update, but not both. If you have enabled dynamic
   update for a zone using the "allow-update" option, you are not supposed
   to edit the zone file by hand, and the server will not attempt to
   reload it.

Q: Why is named listening on UDP port other than 53?

A: Named uses a system selected port to make queries of other nameservers.
   This behaviour can be overridden by using query-source to lock down the
   port and/or address. See also notify-source and transfer-source.

Q: I get warning messages like "zone example.com/IN: refresh: failure
   trying master 1.2.3.4#53: timed out".

A: Check that you can make UDP queries from the slave to the master

   dig +norec example.com soa @1.2.3.4

   You could be generating queries faster than the slave can cope with.
   Lower the serial query rate.

   serial-query-rate 5; // default 20

Q: I don't get RRSIG's returned when I use "dig +dnssec".

A: You need to ensure DNSSEC is enabled (dnssec-enable yes;).

Q: Can a NS record refer to a CNAME.

A: No. The rules for glue (copies of the *address* records in the parent
   zones) and additional section processing do not allow it to work.

   You would have to add both the CNAME and address records (A/AAAA) as
   glue to the parent zone and have CNAMEs be followed when doing
   additional section processing to make it work. No nameserver
   implementation supports either of these requirements.

Q: What does "RFC 1918 response from Internet for 0.0.0.10.IN-ADDR.ARPA"
   mean?

A: If the IN-ADDR.ARPA name covered refers to a internal address space you
   are using then you have failed to follow RFC 1918 usage rules and are
   leaking queries to the Internet. You should establish your own zones
   for these addresses to prevent you querying the Internet's name servers
   for these addresses. Please see http://as112.net/ for details of the
   problems you are causing and the counter measures that have had to be
   deployed.

   If you are not using these private addresses then a client has queried
   for them. You can just ignore the messages, get the offending client to
   stop sending you these messages as they are most probably leaking them
   or setup your own zones empty zones to serve answers to these queries.

   zone "10.IN-ADDR.ARPA" {
           type master;
           file "empty";
   };

   zone "16.172.IN-ADDR.ARPA" {
           type master;
           file "empty";
   };

   ...

   zone "31.172.IN-ADDR.ARPA" {
           type master;
           file "empty";
   };

   zone "168.192.IN-ADDR.ARPA" {
           type master;
           file "empty";
   };

   empty:
   @ 10800 IN SOA <name-of-server>. <contact-email>. (
                  1 3600 1200 604800 10800 )
   @ 10800 IN NS <name-of-server>.

   Note

   Future versions of named are likely to do this automatically.

Q: Will named be affected by the 2007 changes to daylight savings rules in
   the US.

A: No, so long as the machines internal clock (as reported by "date -u")
   remains at UTC. The only visible change if you fail to upgrade your OS,
   if you are in a affected area, will be that log messages will be a hour
   out during the period where the old rules do not match the new rules.

   For most OS's this change just means that you need to update the
   conversion rules from UTC to local time. Normally this involves
   updating a file in /etc (which sets the default timezone for the
   machine) and possibly a directory which has all the conversion rules
   for the world (e.g. /usr/share/zoneinfo). When updating the OS do not
   forget to update any chroot areas as well. See your OS's documentation
   for more details.

   The local timezone conversion rules can also be done on a individual
   basis by setting the TZ environment variable appropriately. See your
   OS's documentation for more details.

Q: Is there a bugzilla (or other tool) database that mere mortals can have
   (read-only) access to for bind?

A: No. The BIND 9 bug database is kept closed for a number of reasons.
   These include, but are not limited to, that the database contains
   proprietory information from people reporting bugs. The database has in
   the past and may in future contain unfixed bugs which are capable of
   bringing down most of the Internet's DNS infrastructure.

   The release pages for each version contain up to date lists of bugs
   that have been fixed post release. That is as close as we can get to
   providing a bug database.

4. Operating-System Specific Questions

4.1. HPUX

Q: I get the following error trying to configure BIND:

   checking if unistd.h or sys/types.h defines fd_set... no
   configure: error: need either working unistd.h or sys/select.h

A: You have attempted to configure BIND with the bundled C compiler. This
   compiler does not meet the minimum compiler requirements to for
   building BIND. You need to install a ANSI C compiler and / or teach
   configure how to find the ANSI C compiler. The later can be done by
   adjusting the PATH environment variable and / or specifying the
   compiler via CC.

   ./configure CC=<compiler> ...

4.2. Linux

Q: Why do I get the following errors:

   general: errno2result.c:109: unexpected error:
   general: unable to convert errno to isc_result: 14: Bad address
   client: UDP client handler shutting down due to fatal receive error: unexpected error

A: This is the result of a Linux kernel bug.

   See: http://marc.theaimsgroup.com/?l=linux-netdev&m=113081708031466&w=2

Q: Why do I see 5 (or more) copies of named on Linux?

A: Linux threads each show up as a process under ps. The approximate
   number of threads running is n+4, where n is the number of CPUs. Note
   that the amount of memory used is not cumulative; if each process is
   using 10M of memory, only a total of 10M is used.

   Newer versions of Linux's ps command hide the individual threads and
   require -L to display them.

Q: Why does BIND 9 log "permission denied" errors accessing its
   configuration files or zones on my Linux system even though it is
   running as root?

A: On Linux, BIND 9 drops most of its root privileges on startup. This
   including the privilege to open files owned by other users. Therefore,
   if the server is running as root, the configuration files and zone
   files should also be owned by root.

Q: I get the error message "named: capset failed: Operation not permitted"
   when starting named.

A: The capability module, part of "Linux Security Modules/LSM", has not
   been loaded into the kernel. See insmod(8).

Q: I'm running BIND on Red Hat Enterprise Linux or Fedora Core -

   Why can't named update slave zone database files?

   Why can't named create DDNS journal files or update the master zones
   from journals?

   Why can't named create custom log files?

A: Red Hat Security Enhanced Linux (SELinux) policy security protections :

   Red Hat have adopted the National Security Agency's SELinux security
   policy ( see http://www.nsa.gov/selinux ) and recommendations for BIND
   security , which are more secure than running named in a chroot and
   make use of the bind-chroot environment unnecessary .

   By default, named is not allowed by the SELinux policy to write, create
   or delete any files EXCEPT in these directories:

   $ROOTDIR/var/named/slaves
   $ROOTDIR/var/named/data
   $ROOTDIR/var/tmp


   where $ROOTDIR may be set in /etc/sysconfig/named if bind-chroot is
   installed.

   The SELinux policy particularly does NOT allow named to modify the
   $ROOTDIR/var/named directory, the default location for master zone
   database files.

   SELinux policy overrules file access permissions - so even if all the
   files under /var/named have ownership named:named and mode rw-rw-r--,
   named will still not be able to write or create files except in the
   directories above, with SELinux in Enforcing mode.

   So, to allow named to update slave or DDNS zone files, it is best to
   locate them in $ROOTDIR/var/named/slaves, with named.conf zone
   statements such as:

   zone "slave.zone." IN {
           type slave;
           file "slaves/slave.zone.db";
           ...
   };
   zone "ddns.zone." IN  {
           type master;
           allow-updates {...};
           file "slaves/ddns.zone.db";
   };


   To allow named to create its cache dump and statistics files, for
   example, you could use named.conf options statements such as:

   options {
           ...
           dump-file "/var/named/data/cache_dump.db";
           statistics-file "/var/named/data/named_stats.txt";
           ...
   };


   You can also tell SELinux to allow named to update any zone database
   files, by setting the SELinux tunable boolean parameter
   'named_write_master_zones=1', using the system-config-securitylevel
   GUI, using the 'setsebool' command, or in /etc/selinux/targeted/
   booleans.

   You can disable SELinux protection for named entirely by setting the
   'named_disable_trans=1' SELinux tunable boolean parameter.

   The SELinux named policy defines these SELinux contexts for named:

   named_zone_t : for zone database files       - $ROOTDIR/var/named/*
   named_conf_t : for named configuration files - $ROOTDIR/etc/{named,rndc}.*
   named_cache_t: for files modifiable by named - $ROOTDIR/var/{tmp,named/{slaves,data}}


   If you want to retain use of the SELinux policy for named, and put
   named files in different locations, you can do so by changing the
   context of the custom file locations .

   To create a custom configuration file location, e.g. '/root/
   named.conf', to use with the 'named -c' option, do:

   # chcon system_u:object_r:named_conf_t /root/named.conf


   To create a custom modifiable named data location, e.g. '/var/log/
   named' for a log file, do:

   # chcon system_u:object_r:named_cache_t /var/log/named


   To create a custom zone file location, e.g. /root/zones/, do:

   # chcon system_u:object_r:named_zone_t /root/zones/{.,*}


   See these man-pages for more information : selinux(8), named_selinux
   (8), chcon(1), setsebool(8)

4.3. Windows

Q: Zone transfers from my BIND 9 master to my Windows 2000 slave fail.
   Why?

A: This may be caused by a bug in the Windows 2000 DNS server where DNS
   messages larger than 16K are not handled properly. This can be worked
   around by setting the option "transfer-format one-answer;". Also check
   whether your zone contains domain names with embedded spaces or other
   special characters, like "John\032Doe\213s\032Computer", since such
   names have been known to cause Windows 2000 slaves to incorrectly
   reject the zone.

Q: I get "Error 1067" when starting named under Windows.

A: This is the service manager saying that named exited. You need to
   examine the Application log in the EventViewer to find out why.

   Common causes are that you failed to create "named.conf" (usually "C:\
   windows\dns\etc\named.conf") or failed to specify the directory in
   named.conf.

   options {
           Directory "C:\windows\dns\etc";
   };

4.4. FreeBSD

Q: I have FreeBSD 4.x and "rndc-confgen -a" just sits there.

A: /dev/random is not configured. Use rndcontrol(8) to tell the kernel to
   use certain interrupts as a source of random events. You can make this
   permanent by setting rand_irqs in /etc/rc.conf.

   /etc/rc.conf
   rand_irqs="3 14 15"

   See also http://people.freebsd.org/~dougb/randomness.html

4.5. Solaris

Q: How do I integrate BIND 9 and Solaris SMF

A: Sun has a blog entry describing how to do this.

   http://blogs.sun.com/roller/page/anay/Weblog?catname=%2FSolaris

4.6. Apple Mac OS X

Q: How do I run BIND 9 on Apple Mac OS X?

A: If you run Tiger(Mac OS 10.4) or later then this is all you need to do:

   % sudo rndc-confgen  > /etc/rndc.conf

   Copy the key statement from /etc/rndc.conf into /etc/rndc.key, e.g.:

   key "rndc-key" {
           algorithm hmac-md5;
           secret "uvceheVuqf17ZwIcTydddw==";
   };

   Then start the relevant service:

   % sudo service org.isc.named start

   This is persistent upon a reboot, so you will have to do it only once.

A: Alternatively you can just generate /etc/rndc.key by running:

   % sudo rndc-confgen -a

   Then start the relevant service:

   % sudo service org.isc.named start

   Named will look for /etc/rndc.key when it starts if it doesn't have a
   controls section or the existing controls are missing keys sub-clauses.
   This is persistent upon a reboot, so you will have to do it only once.