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bind/FAQ
Mark Andrews 0bec2ce285 SE Linux
2005-12-21 02:15:31 +00:00

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Frequently Asked Questions about BIND 9
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Q: Why doesn't -u work on Linux 2.2.x when I build with --enable-threads?
A: Linux threads do not fully implement the Posix threads (pthreads)
standard. In particular, setuid() operates only on the current thread, not
the full process. Because of this limitation, BIND 9 cannot use setuid()
on Linux as it can on all other supported platforms. setuid() cannot be
called before creating threads, since the server does not start listening
on reserved ports until after threads have started.
In the 2.2.18 or 2.3.99-pre3 and newer kernels, the ability to preserve
capabilities across a setuid() call is present. This allows BIND 9 to call
setuid() early, while retaining the ability to bind reserved ports. This
is a Linux-specific hack.
On a 2.2 kernel, BIND 9 does drop many root privileges, so it should be
less of a security risk than a root process that has not dropped
privileges.
If Linux threads ever work correctly, this restriction will go away.
Configuring BIND9 with the --disable-threads option (the default) causes a
non-threaded version to be built, which will allow -u to be used.
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 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 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.
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: 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 produce a usable core file from a multithreaded named on Linux?
A: If the Linux kernel is 2.4.7 or newer, multithreaded core dumps are usable
(that is, the correct thread is dumped). Otherwise, if using a 2.2 kernel,
apply the kernel patch found in contrib/linux/coredump-patch and rebuild
the kernel. This patch will cause multithreaded programs to dump the
correct thread.
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 installed BIND 9 and restarted named, but it's still BIND 8. Why?
A: BIND 9 is installed under /usr/local by default. BIND 8 is often installed
under /usr. Check that the correct named is running.
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'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: I have a BIND 9 master and a BIND 8.2.3 slave, and the master is logging
error messages like "notify to 10.0.0.1#53 failed: unexpected end of
input". What's wrong?
A: This error message is caused by a known bug in BIND 8.2.3 and is fixed in
BIND 8.2.4. It can be safely ignored - the notify has been acted on by the
slave despite the error message.
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: 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: 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: 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: 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: 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 10.0.0.2 { 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 10.0.0.1 { keys external; };
recursion no;
...
};
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
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 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 existance (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: 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: 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 { !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 { 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. Forgeting 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 timzone
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 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 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 don't get RRSIG's returned when I use "dig +dnssec".
A: You need to ensure DNSSEC is enabled (dnssec-enable yes;).
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";
};
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: How do I intergrate 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
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 namesever 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 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.
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: 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 unecessary .
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, eg. '/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, eg. '/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, eg. /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)
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