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FAQ.xml
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<!--
- Copyright (C) 2000-2010, 2013-2016 Internet Systems Consortium, Inc. ("ISC")
-
- This Source Code Form is subject to the terms of the Mozilla Public
- License, v. 2.0. If a copy of the MPL was not distributed with this
- file, You can obtain one at http://mozilla.org/MPL/2.0/.
-->
<!-- Converted by db4-upgrade version 1.0 -->
<article xmlns="http://docbook.org/ns/docbook" version="5.0" class="faq">
<articleinfo>
<copyright>
<year>2000</year>
<year>2001</year>
<year>2002</year>
<year>2003</year>
<year>2004</year>
<year>2005</year>
<year>2006</year>
<year>2007</year>
<year>2008</year>
<year>2009</year>
<year>2010</year>
<year>2013</year>
<year>2014</year>
<year>2015</year>
<year>2016</year>
<holder>Internet Systems Consortium, Inc. ("ISC")</holder>
</copyright>
</articleinfo>
<qandaset defaultlabel="qanda">
<qandadiv><title>Compilation and Installation Questions</title>
<qandaentry>
<question>
<para>
I'm trying to compile BIND 9, and "make" is failing due to
files not being found. Why?
</para>
</question>
<answer>
<para>
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.
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
Isn't "make install" supposed to generate a default named.conf?
</para>
</question>
<answer>
<para>
Short Answer: No.
</para>
<para>
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.
</para>
<para>
What addresses to listen on? For a laptop on the move a lot
you may only want to listen on the loop back interfaces.
</para>
<para>
To whom do you offer recursive service? Is there a 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.
</para>
</answer>
</qandaentry>
</qandadiv> <!-- Compilation and Installation Questions -->
<qandadiv><title>Configuration and Setup Questions</title>
<qandaentry>
<!-- configuration, log -->
<question>
<para>
Why does named log the warning message <quote>no TTL specified -
using SOA MINTTL instead</quote>?
</para>
</question>
<answer>
<para>
Your zone file is illegal according to RFC1035. It must either
have a line like:
</para>
<informalexample>
<programlisting>
$TTL 86400</programlisting>
</informalexample>
<para>
at the beginning, or the first record in it must have a TTL field,
like the "84600" in this example:
</para>
<informalexample>
<programlisting>
example.com. 86400 IN SOA ns hostmaster ( 1 3600 1800 1814400 3600 )</programlisting>
</informalexample>
</answer>
</qandaentry>
<qandaentry>
<!-- configuration -->
<question>
<para>
Why do I get errors like <quote>dns_zone_load: zone foo/IN: loading
master file bar: ran out of space</quote>?
</para>
</question>
<answer>
<para>
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.
</para>
</answer>
</qandaentry>
<qandaentry>
<!-- security -->
<question>
<para>
How do I restrict people from looking up the server version?
</para>
</question>
<answer>
<para>
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.
</para>
</answer>
</qandaentry>
<qandaentry>
<!-- security -->
<question>
<para>
How do I restrict only remote users from looking up the
server version?
</para>
</question>
<answer>
<para>
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.
</para>
<informalexample>
<programlisting>
view "chaos" chaos {
match-clients { <those to be refused>; };
allow-query { none; };
zone "." {
type hint;
file "/dev/null"; // or any empty file
};
};</programlisting>
</informalexample>
</answer>
</qandaentry>
<qandaentry>
<!-- configuration -->
<question>
<para>
What do <quote>no source of entropy found</quote> or <quote>could not
open entropy source foo</quote> mean?
</para>
</question>
<answer>
<para>
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.
</para>
</answer>
</qandaentry>
<qandaentry>
<!-- configuration -->
<question>
<para>
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?
</para>
</question>
<answer>
<para>
This may be a clock skew problem. Check that the the clocks
on the client and server are properly synchronized (e.g.,
using ntp).
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
I see a log message like the following. Why?
</para>
<para>
couldn't open pid file '/var/run/named.pid': Permission denied
</para>
</question>
<answer>
<para>
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 user named is running as).
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
I can query the nameserver from the nameserver but not from other
machines. Why?
</para>
</question>
<answer>
<para>
This is usually the result of the firewall configuration stopping
the queries and / or the replies.
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
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.
</para>
</question>
<answer>
<para>
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.
</para>
<informalexample>
<programlisting>
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;</programlisting>
</informalexample>
<para>
You put the external address on the alias so that all the other
dns clients on these boxes see the internal view by default.
</para>
</answer>
<answer>
<para>
BIND 9.3 and later: Use TSIG to select the appropriate view.
</para>
<informalexample>
<programlisting>
Master 10.0.1.1:
key "external" {
algorithm hmac-sha256;
secret "xxxxxxxxxxxxxxxxxxxxxxxx";
};
view "internal" {
match-clients { !key external; // reject message ment for the
// external view.
10.0.1/24; }; // accept from these addresses.
...
};
view "external" {
match-clients { key external; any; };
server 10.0.1.2 { keys external; }; // tag messages from the
// external view to the
// other servers for the
// view.
recursion no;
...
};
Slave 10.0.1.2:
key "external" {
algorithm hmac-sha256;
secret "xxxxxxxxxxxxxxxxxxxxxxxx";
};
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;
...
};</programlisting>
</informalexample>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
I get error messages like <quote>multiple RRs of singleton type</quote>
and <quote>CNAME and other data</quote> when transferring a zone. What
does this mean?
</para>
</question>
<answer>
<para>
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.
</para>
<informalexample>
<programlisting>
dig axfr example.com @master-server > tmp
named-checkzone example.com tmp</programlisting>
</informalexample>
<para>
A CNAME record cannot exist with the same name as another record
except for the DNSSEC records which prove its existence (NSEC).
</para>
<para>
RFC 1034, Section 3.6.2: <quote>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.</quote>
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
I get error messages like <quote>named.conf:99: unexpected end
of input</quote> where 99 is the last line of named.conf.
</para>
</question>
<answer>
<para>
There are unbalanced quotes in named.conf.
</para>
</answer>
<answer>
<para>
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.
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
How do I share a dynamic zone between multiple views?
</para>
</question>
<answer>
<para>
You choose one view to be master and the second a slave and
transfer the zone between views.
</para>
<informalexample>
<programlisting>
Master 10.0.1.1:
key "external" {
algorithm hmac-sha256;
secret "xxxxxxxxxxxxxxxxxxxxxxxx";
};
key "mykey" {
algorithm hmac-sha256;
secret "yyyyyyyyyyyyyyyyyyyyyyyy";
};
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; };
also-notify { 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 { ... };
};
};</programlisting>
</informalexample>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
I get a error message like <quote>zone wireless.ietf56.ietf.org/IN:
loading master file primaries/wireless.ietf56.ietf.org: no
owner</quote>.
</para>
</question>
<answer>
<para>
This error is produced when a line in the master file
contains leading white space (tab/space) but there 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.
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
Why are my logs in GMT (UTC).
</para>
</question>
<answer>
<para>
You are running chrooted (-t) and have not supplied local timezone
information in the chroot area.
</para>
<simplelist type="vert">
<member>FreeBSD: /etc/localtime</member>
<member>Solaris: /etc/TIMEZONE and /usr/share/lib/zoneinfo</member>
<member>OSF: /etc/zoneinfo/localtime</member>
</simplelist>
<para>
See also tzset(3) and zic(8).
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
I get <quote>rndc: connect failed: connection refused</quote> when
I try to run rndc.
</para>
</question>
<answer>
<para>
This is usually a configuration error.
</para>
<para>
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.
</para>
<para>
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.
</para>
<para>
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).
</para>
<para>
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.
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
I get <quote>transfer of 'example.net/IN' from 192.168.4.12#53:
failed while receiving responses: permission denied</quote> error
messages.
</para>
</question>
<answer>
<para>
These indicate a filesystem permission error preventing
named creating / renaming the temporary file. These will
usually also have other associated error messages like
</para>
<informalexample>
<programlisting>
"dumping master file: sl/tmp-XXXX5il3sQ: open: permission denied"</programlisting>
</informalexample>
<para>
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.
</para>
<para>
Note file names are relative to the directory specified in
options and any chroot directory ([<chroot
dir>/][<options dir>]).
</para>
<informalexample>
<para>
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.
</para>
<programlisting>
options {
directory "/var/named";
};
zone "example.net" {
type slave;
file "sl/example.net";
masters { 192.168.4.12; };
};</programlisting>
</informalexample>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
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.
</para>
<para>
How do I achieve this ?
</para>
</question>
<answer>
<programlisting>
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; };
};
</programlisting>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
Can you help me understand how BIND 9 uses memory to store
DNS zones?
</para>
<para>
Some times it seems to take several times the amount of
memory it needs to store the zone.
</para>
</question>
<answer>
<para>
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.
</para>
<para>
e.g. Ones that are transferring out, the one that it is
serving and the one that is loading.
</para>
<para>
BIND 8 destroyed the zone before loading and also killed
off outgoing transfers of the zone.
</para>
<para>
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.
</para>
<para>
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.
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
I want to use IPv6 locally but I don't have a external IPv6
connection. External lookups are slow.
</para>
</question>
<answer>
<para>
You can use server clauses to stop named making external lookups
over IPv6.
</para>
<programlisting>
server fd81:ec6c:bd62::/48 { bogus no; }; // site ULA prefix
server ::/0 { bogus yes; };
</programlisting>
</answer>
</qandaentry>
</qandadiv> <!-- Configuration and Setup Questions -->
<qandadiv><title>Operations Questions</title>
<qandaentry>
<question>
<para>
How to change the nameservers for a zone?
</para>
</question>
<answer>
<para>
Step 1: Ensure all nameservers, new and old, are serving the
same zone content.
</para>
<para>
Step 2: Work out the maximum TTL of the NS RRset in the parent and child
zones. This is the time it will take caches to be clear of a
particular version of the NS RRset.
If you are just removing nameservers you can skip to Step 6.
</para>
<para>
Step 3: Add new nameservers to the NS RRset for the zone and
wait until all the servers for the zone are answering with this
new NS RRset.
</para>
<para>
Step 4: Inform the parent zone of the new NS RRset then wait for all the
parent servers to be answering with the new NS RRset.
</para>
<para>
Step 5: Wait for cache to be clear of the old NS RRset.
See Step 2 for how long.
If you are just adding nameservers you are done.
</para>
<para>
Step 6: Remove any old nameservers from the zones NS RRset and
wait for all the servers for the zone to be serving the new NS RRset.
</para>
<para>
Step 7: Inform the parent zone of the new NS RRset then wait for all the
parent servers to be answering with the new NS RRset.
</para>
<para>
Step 8: Wait for cache to be clear of the old NS RRset.
See Step 2 for how long.
</para>
<para>
Step 9: Turn off the old nameservers or remove the zone entry from
the configuration of the old nameservers.
</para>
<para>
Step 10: Increment the serial number and wait for the change to
be visible in all nameservers for the zone. This ensures that
zone transfers are still working after the old servers are
decommissioned.
</para>
<para>
Note: the above procedure is designed to be transparent
to dns clients. Decommissioning the old servers too early
will result in some clients not being able to look up
answers in the zone.
</para>
<para>
Note: while it is possible to run the addition and removal
stages together it is not recommended.
</para>
</answer>
</qandaentry>
</qandadiv> <!-- Operations Questions -->
<qandadiv><title>General Questions</title>
<qandaentry>
<question>
<para>
I keep getting log messages like the following. Why?
</para>
<para>
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)
</para>
</question>
<answer>
<para>
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.
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
I keep getting log messages like the following. Why?
</para>
<para>
Jun 21 12:00:00.000 client 10.0.0.1#1234: update denied
</para>
</question>
<answer>
<para>
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
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://support.microsoft.com/support/kb/articles/q246/8/04.asp">
<http://support.microsoft.com/support/kb/articles/q246/8/04.asp></link>
for information about how to turn them off.
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
When I do a "dig . ns", many of the A records for the root
servers are missing. Why?
</para>
</question>
<answer>
<para>
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.
</para>
<para>
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.
</para>
<para>
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".
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
Why don't my zones reload when I do an "rndc reload" or SIGHUP?
</para>
</question>
<answer>
<para>
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.
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
Why is named listening on UDP port other than 53?
</para>
</question>
<answer>
<para>
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.
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
I get warning messages like <quote>zone example.com/IN: refresh:
failure trying master 1.2.3.4#53: timed out</quote>.
</para>
</question>
<answer>
<para>
Check that you can make UDP queries from the slave to the master
</para>
<informalexample>
<programlisting>
dig +norec example.com soa @1.2.3.4</programlisting>
</informalexample>
<para>
You could be generating queries faster than the slave can
cope with. Lower the serial query rate.
</para>
<informalexample>
<programlisting>
serial-query-rate 5; // default 20</programlisting>
</informalexample>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
I don't get RRSIG's returned when I use "dig +dnssec".
</para>
</question>
<answer>
<para>
You need to ensure DNSSEC is enabled (dnssec-enable yes;).
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
Can a NS record refer to a CNAME.
</para>
</question>
<answer>
<para>
No. The rules for glue (copies of the *address* records
in the parent zones) and additional section processing do
not allow it to work.
</para>
<para>
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.
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
What does <quote>RFC 1918 response from Internet for
0.0.0.10.IN-ADDR.ARPA</quote> mean?
</para>
</question>
<answer>
<para>
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 <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://as112.net/"><http://as112.net/></link>
for details of the problems you are causing and the counter
measures that have had to be deployed.
</para>
<para>
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.
</para>
<informalexample>
<programlisting>
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>.</programlisting>
</informalexample>
<para>
<note>
Future versions of named are likely to do this automatically.
</note>
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
Will named be affected by the 2007 changes to daylight savings
rules in the US.