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@@ -0,0 +1,675 @@ +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. + |