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Frequently Asked Questions about BIND 9
Copyright © 2004-2007 Internet Systems Consortium, Inc. ("ISC")
Copyright © 2000-2003 Internet Software Consortium.
-------------------------------------------------------------------------------
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.
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: 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 10.0.1.2 { 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 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)
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: 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 documetation for more details.
The local timezone conversion rules can also be done on a individual basis by
setting the TZ envirionment variable appropriately. See your OS's documentation
for more details.
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