526 lines
21 KiB
Plaintext
526 lines
21 KiB
Plaintext
Frequently Asked Questions about BIND 9
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-------------------------------------------------------------------------------
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Q: Why doesn't -u work on Linux 2.2.x when I build with --enable-threads?
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A: Linux threads do not fully implement the Posix threads (pthreads) standard.
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In particular, setuid() operates only on the current thread, not the full
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process. Because of this limitation, BIND 9 cannot use setuid() on Linux as
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it can on all other supported platforms. setuid() cannot be called before
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creating threads, since the server does not start listening on reserved
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ports until after threads have started.
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In the 2.2.18 or 2.3.99-pre3 and newer kernels, the ability to preserve
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capabilities across a setuid() call is present. This allows BIND 9 to call
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setuid() early, while retaining the ability to bind reserved ports. This is
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a Linux-specific hack.
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On a 2.2 kernel, BIND 9 does drop many root privileges, so it should be less
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of a security risk than a root process that has not dropped privileges.
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If Linux threads ever work correctly, this restriction will go away.
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Configuring BIND9 with the --disable-threads option (the default) causes a
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non-threaded version to be built, which will allow -u to be used.
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Q: Why does named log the warning message "no TTL specified - using SOA MINTTL
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instead"?
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A: Your zone file is illegal according to RFC1035. It must either have a line
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like:
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$TTL 86400
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at the beginning, or the first record in it must have a TTL field, like the
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"84600" in this example:
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example.com. 86400 IN SOA ns hostmaster ( 1 3600 1800 1814400 3600 )
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Q: Why do I see 5 (or more) copies of named on Linux?
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A: Linux threads each show up as a process under ps. The approximate number of
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threads running is n+4, where n is the number of CPUs. Note that the amount
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of memory used is not cumulative; if each process is using 10M of memory,
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only a total of 10M is used.
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Q: Why does BIND 9 log "permission denied" errors accessing its configuration
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files or zones on my Linux system even though it is running as root?
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A: On Linux, BIND 9 drops most of its root privileges on startup. This
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including the privilege to open files owned by other users. Therefore, if
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the server is running as root, the configuration files and zone files should
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also be owned by root.
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Q: Why do I get errors like "dns_zone_load: zone foo/IN: loading master file
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bar: ran out of space"?
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A: This is often caused by TXT records with missing close quotes. Check that
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all TXT records containing quoted strings have both open and close quotes.
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Q: How do I produce a usable core file from a multithreaded named on Linux?
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A: If the Linux kernel is 2.4.7 or newer, multithreaded core dumps are usable
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(that is, the correct thread is dumped). Otherwise, if using a 2.2 kernel,
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apply the kernel patch found in contrib/linux/coredump-patch and rebuild the
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kernel. This patch will cause multithreaded programs to dump the correct
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thread.
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Q: How do I restrict people from looking up the server version?
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A: Put a "version" option containing something other than the real version in
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the "options" section of named.conf. Note doing this will not prevent
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attacks and may impede people trying to diagnose problems with your server.
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Also it is possible to "fingerprint" nameservers to determine their version.
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Q: How do I restrict only remote users from looking up the server version?
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A: The following view statement will intercept lookups as the internal view
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that holds the version information will be matched last. The caveats of the
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previous answer still apply, of course.
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view "chaos" chaos {
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match-clients { <those to be refused>; };
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allow-query { none; };
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zone "." {
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type hint;
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file "/dev/null"; // or any empty file
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};
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};
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Q: What do "no source of entropy found" or "could not open entropy source foo"
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mean?
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A: The server requires a source of entropy to perform certain operations,
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mostly DNSSEC related. These messages indicate that you have no source of
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entropy. On systems with /dev/random or an equivalent, it is used by
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default. A source of entropy can also be defined using the random-device
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option in named.conf.
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Q: I installed BIND 9 and restarted named, but it's still BIND 8. Why?
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A: BIND 9 is installed under /usr/local by default. BIND 8 is often installed
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under /usr. Check that the correct named is running.
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Q: I'm trying to use TSIG to authenticate dynamic updates or zone transfers.
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I'm sure I have the keys set up correctly, but the server is rejecting the
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TSIG. Why?
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A: This may be a clock skew problem. Check that the the clocks on the client
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and server are properly synchronised (e.g., using ntp).
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Q: I'm trying to compile BIND 9, and "make" is failing due to files not being
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found. Why?
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A: Using a parallel or distributed "make" to build BIND 9 is not supported, and
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doesn't work. If you are using one of these, use normal make or gmake
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instead.
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Q: I have a BIND 9 master and a BIND 8.2.3 slave, and the master is logging
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error messages like "notify to 10.0.0.1#53 failed: unexpected end of input".
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What's wrong?
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A: This error message is caused by a known bug in BIND 8.2.3 and is fixed in
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BIND 8.2.4. It can be safely ignored - the notify has been acted on by the
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slave despite the error message.
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Q: I keep getting log messages like the following. Why?
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Dec 4 23:47:59 client 10.0.0.1#1355: updating zone 'example.com/IN': update
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failed: 'RRset exists (value dependent)' prerequisite not satisfied
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(NXRRSET)
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A: DNS updates allow the update request to test to see if certain conditions
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are met prior to proceeding with the update. The message above is saying
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that conditions were not met and the update is not proceeding. See doc/rfc/
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rfc2136.txt for more details on prerequisites.
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Q: I keep getting log messages like the following. Why?
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Jun 21 12:00:00.000 client 10.0.0.1#1234: update denied
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A: Someone is trying to update your DNS data using the RFC2136 Dynamic Update
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protocol. Windows 2000 machines have a habit of sending dynamic update
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requests to DNS servers without being specifically configured to do so. If
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the update requests are coming from a Windows 2000 machine, see http://
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support.microsoft.com/support/kb/articles/q246/8/04.asp for information
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about how to turn them off.
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Q: I see a log message like the following. Why?
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couldn't open pid file '/var/run/named.pid': Permission denied
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A: You are most likely running named as a non-root user, and that user does not
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have permission to write in /var/run. The common ways of fixing this are to
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create a /var/run/named directory owned by the named user and set pid-file
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to "/var/run/named/named.pid", or set pid-file to "named.pid", which will
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put the file in the directory specified by the directory option (which, in
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this case, must be writable by the named user).
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Q: When I do a "dig . ns", many of the A records for the root servers are
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missing. Why?
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A: This is normal and harmless. It is a somewhat confusing side effect of the
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way BIND 9 does RFC2181 trust ranking and of the efforts BIND 9 makes to
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avoid promoting glue into answers.
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When BIND 9 first starts up and primes its cache, it receives the root
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server addresses as additional data in an authoritative response from a root
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server, and these records are eligible for inclusion as additional data in
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responses. Subsequently it receives a subset of the root server addresses as
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additional data in a non-authoritative (referral) response from a root
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server. This causes the addresses to now be considered non-authoritative
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(glue) data, which is not eligible for inclusion in responses.
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The server does have a complete set of root server addresses cached at all
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times, it just may not include all of them as additional data, depending on
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whether they were last received as answers or as glue. You can always look
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up the addresses with explicit queries like "dig a.root-servers.net A".
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Q: Zone transfers from my BIND 9 master to my Windows 2000 slave fail. Why?
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A: This may be caused by a bug in the Windows 2000 DNS server where DNS
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messages larger than 16K are not handled properly. This can be worked around
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by setting the option "transfer-format one-answer;". Also check whether your
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zone contains domain names with embedded spaces or other special characters,
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like "John\032Doe\213s\032Computer", since such names have been known to
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cause Windows 2000 slaves to incorrectly reject the zone.
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Q: Why don't my zones reload when I do an "rndc reload" or SIGHUP?
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A: A zone can be updated either by editing zone files and reloading the server
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or by dynamic update, but not both. If you have enabled dynamic update for a
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zone using the "allow-update" option, you are not supposed to edit the zone
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file by hand, and the server will not attempt to reload it.
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Q: I can query the nameserver from the nameserver but not from other machines.
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Why?
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A: This is usually the result of the firewall configuration stopping the
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queries and / or the replies.
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Q: How can I make a server a slave for both an internal and an external view at
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the same time? When I tried, both views on the slave were transferred from
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the same view on the master.
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A: You will need to give the master and slave multiple IP addresses and use
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those to make sure you reach the correct view on the other machine.
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Master: 10.0.1.1 (internal), 10.0.1.2 (external, IP alias)
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internal:
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match-clients { !10.0.1.2; !10.0.1.4; 10.0.1/24; };
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notify-source 10.0.1.1;
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transfer-source 10.0.1.1;
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query-source address 10.0.1.1;
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external:
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match-clients { any; };
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recursion no; // don't offer recursion to the world
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notify-source 10.0.1.2;
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transfer-source 10.0.1.2;
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query-source address 10.0.1.2;
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Slave: 10.0.1.3 (internal), 10.0.1.4 (external, IP alias)
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internal:
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match-clients { !10.0.1.2; !10.0.1.4; 10.0.1/24; };
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notify-source 10.0.1.3;
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transfer-source 10.0.1.3;
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query-source address 10.0.1.3;
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external:
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match-clients { any; };
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recursion no; // don't offer recursion to the world
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notify-source 10.0.1.4;
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transfer-source 10.0.1.4;
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query-source address 10.0.1.4;
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You put the external address on the alias so that all the other dns clients
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on these boxes see the internal view by default.
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A: BIND 9.3 and later: Use TSIG to select the appropriate view.
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Master 10.0.1.1:
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key "external" {
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algorithm hmac-md5;
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secret "xxxxxxxx";
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};
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view "internal" {
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match-clients { !key external; 10.0.1/24; };
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...
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};
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view "external" {
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match-clients { key external; any; };
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server 10.0.0.2 { keys external; };
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recursion no;
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...
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};
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Slave 10.0.1.2:
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key "external" {
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algorithm hmac-md5;
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secret "xxxxxxxx";
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};
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view "internal" {
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match-clients { !key external; 10.0.1/24; };
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...
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};
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view "external" {
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match-clients { key external; any; };
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server 10.0.0.1 { keys external; };
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recursion no;
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...
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};
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Q: I have FreeBSD 4.x and "rndc-confgen -a" just sits there.
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A: /dev/random is not configured. Use rndcontrol(8) to tell the kernel to use
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certain interrupts as a source of random events. You can make this permanent
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by setting rand_irqs in /etc/rc.conf.
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/etc/rc.conf
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rand_irqs="3 14 15"
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See also http://people.freebsd.org/~dougb/randomness.html
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Q: Why is named listening on UDP port other than 53?
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A: Named uses a system selected port to make queries of other nameservers. This
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behaviour can be overridden by using query-source to lock down the port and/
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or address. See also notify-source and transfer-source.
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Q: I get error messages like "multiple RRs of singleton type" and "CNAME and
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other data" when transferring a zone. What does this mean?
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A: These indicate a malformed master zone. You can identify the exact records
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involved by transferring the zone using dig then running named-checkzone on
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it.
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dig axfr example.com @master-server > tmp
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named-checkzone example.com tmp
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A CNAME record cannot exist with the same name as another record except for
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the DNSSEC records which prove its existance (NSEC).
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RFC 1034, Section 3.6.2: "If a CNAME RR is present at a node, no other data
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should be present; this ensures that the data for a canonical name and its
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aliases cannot be different. This rule also insures that a cached CNAME can
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be used without checking with an authoritative server for other RR types."
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Q: I get error messages like "named.conf:99: unexpected end of input" where 99
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is the last line of named.conf.
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A: Some text editors (notepad and wordpad) fail to put a line title indication
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(e.g. CR/LF) on the last line of a text file. This can be fixed by "adding"
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a blank line to the end of the file. Named expects to see EOF immediately
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after EOL and treats text files where this is not met as truncated.
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Q: I get warning messages like "zone example.com/IN: refresh: failure trying
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master 1.2.3.4#53: timed out".
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A: Check that you can make UDP queries from the slave to the master
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dig +norec example.com soa @1.2.3.4
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You could be generating queries faster than the slave can cope with. Lower
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the serial query rate.
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serial-query-rate 5; // default 20
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Q: How do I share a dynamic zone between multiple views?
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A: You choose one view to be master and the second a slave and transfer the
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zone between views.
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Master 10.0.1.1:
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key "external" {
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algorithm hmac-md5;
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secret "xxxxxxxx";
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};
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key "mykey" {
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algorithm hmac-md5;
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secret "yyyyyyyy";
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};
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view "internal" {
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match-clients { !external; 10.0.1/24; };
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server 10.0.1.1 {
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/* Deliver notify messages to external view. */
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keys { external; };
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};
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zone "example.com" {
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type master;
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file "internal/example.db";
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allow-update { key mykey; };
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notify-also { 10.0.1.1; };
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};
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};
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view "external" {
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match-clients { external; any; };
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zone "example.com" {
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type slave;
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file "external/example.db";
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masters { 10.0.1.1; };
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transfer-source { 10.0.1.1; };
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// allow-update-forwarding { any; };
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// allow-notify { ... };
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};
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};
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Q: I get a error message like "zone wireless.ietf56.ietf.org/IN: loading master
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file primaries/wireless.ietf56.ietf.org: no owner".
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A: This error is produced when a line in the master file contains leading white
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space (tab/space) but the is no current record owner name to inherit the
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name from. Usually this is the result of putting white space before a
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comment. Forgeting the "@" for the SOA record or indenting the master file.
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Q: Why are my logs in GMT (UTC).
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A: You are running chrooted (-t) and have not supplied local timzone
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information in the chroot area.
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FreeBSD: /etc/localtime
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Solaris: /etc/TIMEZONE and /usr/share/lib/zoneinfo
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OSF: /etc/zoneinfo/localtime
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See also tzset(3) and zic(8).
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Q: I get the error message "named: capset failed: Operation not permitted" when
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starting named.
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A: The capability module, part of "Linux Security Modules/LSM", has not been
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loaded into the kernel. See insmod(8).
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Q: I get "rndc: connect failed: connection refused" when I try to run rndc.
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A: This is usually a configuration error.
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First ensure that named is running and no errors are being reported at
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startup (/var/log/messages or equivalent). Running "named -g <usual
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arguments>" from a title can help at this point.
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Secondly ensure that named is configured to use rndc either by "rndc-confgen
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-a", rndc-confgen or manually. The Administrators Reference manual has
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details on how to do this.
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Old versions of rndc-confgen used localhost rather than 127.0.0.1 in /etc/
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rndc.conf for the default server. Update /etc/rndc.conf if necessary so that
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the default server listed in /etc/rndc.conf matches the addresses used in
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named.conf. "localhost" has two address (127.0.0.1 and ::1).
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If you use "rndc-confgen -a" and named is running with -t or -u ensure that
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/etc/rndc.conf has the correct ownership and that a copy is in the chroot
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area. You can do this by re-running "rndc-confgen -a" with appropriate -t
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and -u arguments.
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Q: I don't get RRSIG's returned when I use "dig +dnssec".
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A: You need to ensure DNSSEC is enabled (dnssec-enable yes;).
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Q: I get "Error 1067" when starting named under Windows.
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A: This is the service manager saying that named exited. You need to examine
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the Application log in the EventViewer to find out why.
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Common causes are that you failed to create "named.conf" (usually "C:\
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windows\dns\etc\named.conf") or failed to specify the directory in
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named.conf.
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options {
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Directory "C:\windows\dns\etc";
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};
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Q: I get "transfer of 'example.net/IN' from 192.168.4.12#53: failed while
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receiving responses: permission denied" error messages.
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A: These indicate a filesystem permission error preventing named creating /
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renaming the temporary file. These will usually also have other associated
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error messages like
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"dumping master file: sl/tmp-XXXX5il3sQ: open: permission denied"
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Named needs write permission on the directory containing the file. Named
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writes the new cache file to a temporary file then renames it to the name
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specified in named.conf to ensure that the contents are always complete.
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This is to prevent named loading a partial zone in the event of power
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failure or similar interrupting the write of the master file.
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Note file names are relative to the directory specified in options and any
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chroot directory ([<chroot dir>/][<options dir>]).
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If named is invoked as "named -t /chroot/DNS" with the following named.conf
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then "/chroot/DNS/var/named/sl" needs to be writable by the user named is
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running as.
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options {
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directory "/var/named";
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};
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zone "example.net" {
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type slave;
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file "sl/example.net";
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masters { 192.168.4.12; };
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};
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Q: How do I intergrate BIND 9 and Solaris SMF
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A: Sun has a blog entry describing how to do this.
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http://blogs.sun.com/roller/page/anay/Weblog?catname=%2FSolaris
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Q: Can a NS record refer to a CNAME.
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A: No. The rules for glue (copies of the *address* records in the parent zones)
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and additional section processing do not allow it to work.
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You would have to add both the CNAME and address records (A/AAAA) as glue to
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the parent zone and have CNAMEs be followed when doing additional section
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processing to make it work. No namesever implementation supports either of
|
|
these requirements.
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|
|
|
Q: What does "RFC 1918 response from Internet for 0.0.0.10.IN-ADDR.ARPA" mean?
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|
|
|
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 quering 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.
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|
|
|
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.
|
|
|