------------------------------------------------------------------------------- About pdnsd pdnsd is a proxy DNS server with permanent caching (the cache contents are written to hard disk on exit) that is designed to cope with unreachable or down DNS servers (for example in dial-in networking). Since version 1.1.0, pdnsd supports negative caching. It is licensed under the GNU General Public License (GPL). This, in short, means that the sources are distributed togehter with the program, and that you are free to modify the sources and redistribute them as long as you also license them under the GPL. You do not need to pay anything for pdnsd. It also means that there is ABSOLUTELY NO WARRANTY for pdnsd or any part of it. For details, please read the GPL. pdnsd can be used with applications that do DNS lookups, e.g. on startup, and can't be configured to change that behaviour, to prevent the often minute-long hangs (or even crashes) that result from stalled DNS queries. Some Netscape Navigator versions for Unix, for example, expose this behaviour. pdnsd is configurable via a file and supports run-time configuration using the program pdnsd-ctl that comes with pdnsd. This allows you to set the status flags of servers that pdnsd knows (to influence which servers pdnsd will query), and the addition, deletion and invalidation of DNS records in pdnsd's cache. Parallel name server queries are supported. This is a technique that allows querying several servers at the same time so that very slow or unavailable servers will not block the answer for one timeout interval. Since version 1.0.0, pdnsd has full IPv6 support. There is also a limited support for local zone records, intended for defining 1.0.0.127.in-addr.arpa. and localhost. , since some clients request that information and it must be served even if the cached servers are not available or do not serve these records. pdnsd may also read your /etc/hosts file (this file is normally used by your local resolver and usually contains information for localhost as well as for your machines FQDN) and serve its contents. pdnsd was started on Linux, and has since been ported to FreeBSD (and Cygwin and Darwin). 90% of the source code should be easily portable to POSIX- and BSD-compatible systems, provided that those systems support the POSIX threads (pthreads). The rest might need OS-specific rewrites. Currently, pdnsd is only compileable by gcc. This should be easy to fix, but I just do not have documentation for other compilers. If you are not able or do not want to use gcc, I would recommend you just try to do the minor changes. pdnsd must be started as root in some cases (raw sockets are needed for icmp echoes for the option uptest=ping, and the default port is 53, this must be > 1024 to allow non-root execution). However, pdnsd can be configured to change it's user and group id to those of a non-privileged user after opening the sockets needed for this. The server should support the full standard DNS queries following the rfcs 1034 and 1035. As of version 1.0.0, the rfc compliance has been improved again, and pdnsd is now believed (or hoped?) to be fully rfc-compatible. It completely follows rfc 2181 (except for one minor issue in the FreeBSD port, see the documentation). It does not support the following features, of which most are marked optional, experimental or obsolete in these rfcs: * Inverse queries * Status queries * Completion queries * Namespaces other than IN (Internet) * AXFR and IXFR queries (whole zone transfers); since pdnsd does not maintain zones, that should not violate the standard The following record types, that are extensions to the original DNS standard, are supported for caching since version 1.2.9 (if you do not need most of them, you can disable runtime support for the unneeded ones before compiling pdnsd and save a little cache and executable space, see the source file src/ rr_types.in): * RP (responsible person, RFC 1183) * AFSDB (AFS database location, RFC 1183) * X25 (X25 address, RFC 1183) * ISDN (ISDN number/address, RFC 1183) * RT (route through, RFC 1183) * NSAP (Network Service Access Protocol address , RFC 1348) * PX (X.400/RFC822 mapping information, RFC 1995) * GPOS (geographic position, deprecated) * AAAA (IPv6 address, RFC 1886) * LOC (location, RFC 1876) * EID (Nimrod EID) * NIMLOC (Nimrod locator) * SRV (service record, RFC 2782) * ATMA (ATM address) * NAPTR (URI mapping, RFC 2168) * KX (key exchange, RFC 2230) * CERT (Certificate record, RFC 4398) * DS (Delegation Signer, RFC 4034) * RRSIG (Resource Record Signature, RFC 4034) * NSEC (Next Secure, RFC 4034) * DNSKEY (record containing the public key for a zone, RFC 4034) * NSEC3 (Next Secure version 3, RFC 5155) * NSEC3PARAM (NSEC3 parameters, RFC 5155) Note: This list is incomplete. For the complete list see the source file src/ rr_types.in. There are FreeBSD and OpenBSD ports available for pdnsd (ports/net/pdnsd for both). Thanks go to Roman Shterenzon for the FreeBSD port Sebastian Stark for the OpenBSD one! Thanks to Kiyo Kelvin Lee now also runs on the Cygwin platform! Thanks goes to Rodney Brown for extending portability to the Darwin (Apple Mac OS X) platform! If you have questions left, you should take a look into the FAQ. Bugfixes, patches and compatability fixes for other OSs are very welcome! Features in detail This section describes some of pdnsds features in detail. Most of the options are set in the config file. For more information on the configuration file, see the documenation page. Uptests pdnsd provides several methods to test whether a remote DNS server should be regarded as available (so that pdnsd can query it), in addition to the obvious "none" test (the server is always regarded as available, or availability is set on or off using the pdnsd-ctl utility). These tests are: * ping: a given adress is ping'ed in a given interval. If it there is no response or the host is unreachable, the server is seen to be not available (for those who don't know: pinging is sending a certain Internet packet type to a host to which any standard-conformant host is required to reply). * if: a given network interface is tested whether it is existent, up and running. If it is not, the server is regarded to be not available. This is especially useful for ppp and similar interfaces. A special case test for Linux isdn (ippp*) interfaces is integrated, so that the uptests should also work for these. * dev: this is a variant of the if uptest for use with Linux dial-on-demand ppp interfaces. In addition to performing an if-style interface uptest, it also tests whether a specified program (e.g. pppd) owns a lock to a given (modem-) device. * exec: a given shell command line is executed and the exit status of the whole command line (which is normally the exit status of the last command) is evaluated. If it is not zero, the server is regarded to be not available. This is a very flexible testing method with which it should be able to perform virtually any needed test. * query: New in version 1.2: This works like the ping test, except it sends an (empty) DNS query to the remote server. If the server sends a well-formed response back within the timeout period (except SERVFAIL), it will be regarded as available. This test is useful if a remote server does not respond to ICMP_ECHO requests at all, which unfortunately is quite common these days. In many cases this test will be a more reliable indicator of availability than the ones mentioned above. Local Records ("Zones") As mentioned above, there are only very basic local record types (ie the record types that you may use in record declarations in your local configuration for records that pdnsd shall serve in addion to the cached ones). They are organized roughly in zones but have not complete zone declarations, so I generally do not use the term "zone" for them, but rather "local records". These are the local record types pdnsd can understand: * SOA (information about the name server) * A (domain-name-to-address mapping) * PTR (pointer, used normally for address-to-domain-name mapping) * NS (name server, generated automatically by pdnsd for any local record set) * CNAME (canonical host name) * MX (mail exchange for the domain) * TXT (arbitrary text strings, often used for Sender Policy Framework) You can specify these records in the configuration file. You may "source" a file in a format like that used in the /etc/hosts file, that means that pdnsd reads this file, extracts addresses and domain names from it and automatically generates A records for name to address mapping, PTR records for address to name mapping and NS records (name server specifiation) for each entry in the file. Records can also be changed dynamically at run time. A script contributed by Marko Stolle makes pdnsd usable in a DHCP setup using this feature. System requirements As mentioned, pdnsd currently runs under Linux, FreeBSD and Cygwin. Other BSD flavours may or may not work (feedback is very welcome!). The system and software requirements under Linux are: * Kernel version >2.2.0 * glibc version >2.0.1 (aka libc6) with LinuxThreads (normally included) or NPTL (Native Posix Thread Library, recommended). Due to a bug, pdnsd 0.9.8 does not run with glibc2.1.1. This behaviour was fixed in pdnsd 0.9.9. * For IPv6: glibc>=2.1 The system requirements under FreeBSD are: * FreeBSD versions >=2.6 (prior ones may or may not work) * For IPv6: FreeBSD >=4.0 is recommended (no idea if it runs on prior versions) The common software requirements for all supported systems are: * GCC, preferably egcs-2.* or 3.* (other compilers are currently not supported; the needed patch for another compiler should not be difficult, however) * GNU or BSD make * the standard commands install, grep, sed, awk, touch and which (along with the REALLY standard ones mv, cp, ln, rm, pwd, test, echo, cat, mkdir, chown, chmod, tar). In any standard Unix installation, this should be no problem. * for hacking and building own packages, you might also need gzip, bzip2, perl and rpmbuild Download If you want to download pdnsd, please visit the download page. Authors pdnsd was originally written by Thomas Moestl, but is no longer maintained by him. Paul A. Rombouts has revised large portions of the code and has added a number of new features. See README.par and the ChangeLog in the source directory (or /usr/share/doc/pdnsd- if you have installed a binary package) for more details. If you have questions about the recent modifications, you can find the email address of the current maintainer at the end of README.par. Daniel Smolik has contributed RedHat RPMs (the most recent RPMs are available here). Torben Janssen contributed start scripts for Red Hat Linux. Soenke J. Peters contributed patches and suggestions for Red Hat compatability. Wolfgang Ocker has contributed the code and documentation for the server_ip option. Markus Mohr contributed a Debian rc script. Nikita V. Youschenko contributed extensions to the "if" uptest. Lyonel Vincent extended the serve_aliases option to support an arbitrary number of aliases. Sourav K. Mandal wrote the autoconf scripts and contributed many fixes and suggestions. Stephan Boettcher contributed the SCHEME= option. Ron Yorston contributed the uptest for Linux ppp dial-on-demand devices. Alexandre Nunes fixed some bugs in the autoconf files. Sverker Wiberg contributed fixes for IPv6. Carsten Block contributed configure-able rc scripts. Olaf Kirch contributed a security fix for the run_as code. Paul Wagland contributed various patches for bind9-compatability and other issues. Roman Shterenzon contributed patches and lots of helpful hints for FreeBSD compatability. Bernd Leibing has contributed spec file fixes. Michael Wiedmann has contributed the pdnsd-ctl.8 man page. Marko Stolle has contributed the contrib/pdnsd_update.pl script that makes pdnsd usable in a DHCP setup. P.J. Bostley has contributed patches to get pdnsd working on alpha properly. Christian Engstler contributed patches for SuSE compatability. Bjoern Fischer contributed code to make pdnsd leave the case of names in the cache unchanged. Marko Stolle contributed the contrib/pdnsd_update.pl script that makes pdnsd usable in a DHCP setup. Andrew M. Bishop contributed the support for the label server option and the pdnsd-ctl interface for using it. Frank Elsner contributed rc script fixes. Andreas Steinmetz contributed the code for query_port_start and query_port_end options. Mahesh T. Pai contributed the pdnsd.8 man page. Nikola Kotur contributed the Slackware start-up script. Kiyo Kelvin Lee contributed a patch for Cygwin support. Rodney Brown contributed a patch for Darwin (Apple Mac OS X) support. Jan-Marek Glogowski contributed a patch implementing the use_nss option. Special thanks to Bert Frederiks for letting me do a late-night debugging run on his machine to spot obscure bugs! Thanks to the following persons for reporting bugs and being helpful: David G. Andersen, Dirk Armbrust, Daniel Black, Kevin A. Burton, Juliusz Chroboczek, Joachim Dorner, Stefan Erhardt, Stefan F?rster, Mike Hammer, Jonathan Hudson, Dan Jacobson, Byrial Jensen, Patrick Loschmidt, James MacLean, Fraser McCrossan, Michael M?ller, Erich Reitz, Brian Schroeder, Milan P. Stanic, Michael Steiner, Norbert Steinl, Markus Storm, Michael Str?der, Alan Swanson, Eelco Vriezekolk. ------------------------------------------------------------------------------- Thomas Moestl and Paul A. Rombouts Last revised: 17 March 2012 by Paul A. Rombouts