Appendix D. BIND 9 DNS Library Support
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## Appendix D. BIND 9 DNS Library Support

## BIND 9 DNS Library Support

This version of BIND 9 "exports" its internal libraries so that they can be used by third-party applications more easily (we call them "export" libraries in this document). In addition to all major DNS-related APIs BIND 9 is currently using, the export libraries provide the following features:

- The newly created "DNS client" module. This is a higher level API that provides an interface to name resolution, single DNS transaction with a particular server, and dynamic update. Regarding name resolution, it supports advanced features such as DNSSEC validation and caching. This module supports both synchronous and asynchronous mode.

- The new "IRS" (Information Retrieval System) library. It provides an interface to parse the traditional resolv.conf file and more advanced, DNS-specific configuration file for the rest of this package (see the description for the dns.conf file below).

- As part of the IRS library, newly implemented standard address-name mapping functions, getaddrinfo() and getnameinfo(), are provided. They use the DNSSEC-aware validating resolver backend, and could use other advanced features of the BIND 9 libraries such as caching. The getaddrinfo() function resolves both A and AAAA RRs concurrently (when the address family is unspecified).

- An experimental framework to support other event libraries than BIND 9's internal event task system.

### Prerequisite

GNU make is required to build the export libraries (other part of BIND 9 can still be built with other types of make). In the reminder of this document, "make" means GNU make. Note that in some platforms you may need to invoke a different command name than "make" (e.g. "gmake") to indicate it's GNU make.

### Compilation

    $ ./configure --enable-exportlib [other flags]
    $ make

This will create (in addition to usual BIND 9 programs) and a separate set of libraries under the lib/export directory. For example, `lib/export/dns/libdns.a` is the archive file of the export version of the BIND 9 DNS library. Sample application programs using the libraries will also be built under the lib/export/samples directory (see below).

### Installation

    $ cd lib/export
    $ make install

This will install library object files under the directory specified by the --with-export-libdir configure option (default: EPREFIX/lib/bind9), and header files under the directory specified by the --with-export-includedir configure option (default: PREFIX/include/bind9). Root privilege is normally required. "make install" at the top directory will do the same.

To see how to build your own application after the installation, see `lib/export/samples/Makefile-postinstall.in`.

### Known Defects/Restrictions

- Currently, win32 is not supported for the export library. (Normal BIND 9 application can be built as before).

- The "fixed" RRset order is not (currently) supported in the export library. If you want to use "fixed" RRset order for, e.g. named while still building the export library even without the fixed order support, build them separately:

      $ ./configure --enable-fixed-rrset [other flags, but not --enable-exportlib]
      $ make
      $ ./configure --enable-exportlib [other flags, but not --enable-fixed-rrset]
      $ cd lib/export
      $ make

- The client module and the IRS library currently do not support DNSSEC validation using DLV (the underlying modules can handle it, but there is no tunable interface to enable the feature).

- RFC 5011 is not supported in the validating stub resolver of the export library. In fact, it is not clear whether it should: trust anchors would be a system-wide configuration which would be managed by an administrator, while the stub resolver will be used by ordinary applications run by a normal user.

- Not all common `/etc/resolv.conf` options are supported in the IRS library. The only available options in this version are "debug" and "ndots".

### The dns.conf File

The IRS library supports an "advanced" configuration file related to the DNS library for configuration parameters that would be beyond the capability of the `resolv.conf` file. Specifically, it is intended to provide DNSSEC related configuration parameters. By default the path to this configuration file is `/etc/dns.conf`. This module is very experimental and the configuration syntax or library interfaces may change in future versions. Currently, only the trusted-keys statement is supported, whose syntax is the same as the same name of statement for `named.conf`. (See the section called “trusted-keys Statement Grammar” for details.)

### Sample Applications

Some sample application programs using this API are provided for reference. The following is a brief description of these applications.

#### sample: a simple stub resolver utility

It sends a query of a given name (of a given optional RR type) to a specified recursive server, and prints the result as a list of RRs. It can also act as a validating stub resolver if a trust anchor is given via a set of command line options.

Usage: sample [options] server_address hostname

Options and Arguments:

-t RRtype

  specify the RR type of the query. The default is the A RR.

[-a algorithm] [-e] -k keyname -K keystring

  specify a command-line DNS key to validate the answer. For example, to specify the following DNSKEY of example.com:

  example.com. 3600 IN DNSKEY 257 3 5 xxx

  specify the options as follows:

                -e -k example.com -K "xxx"

  -e means that this key is a zone's "key signing key" (as known as "secure Entry point"). When -a is omitted rsasha1 will be used by default.

-s domain:alt_server_address

  specify a separate recursive server address for the specific "domain". Example: -s example.com:2001:db8::1234

server_address

  an IP(v4/v6) address of the recursive server to which queries are sent.

hostname

  the domain name for the query

#### sample-async: a simple stub resolver, working asynchronously

Similar to "sample", but accepts a list of (query) domain names as a separate file and resolves the names asynchronously.

Usage: sample-async [-s server_address] [-t RR_type] input_file

Options and Arguments:

-s server_address
  an IPv4 address of the recursive server to which queries are sent. (IPv6 addresses are not supported in this implementation)
-t RR_type
  specify the RR type of the queries. The default is the A RR.
input_file
  a list of domain names to be resolved. each line consists of a single domain name. Example:

  www.example.com
  mx.example.net
  ns.xxx.example

#### sample-request: a simple DNS transaction client

It sends a query to a specified server, and prints the response with minimal processing. It doesn't act as a "stub resolver": it stops the processing once it gets any response from the server, whether it's a referral or an alias (CNAME or DNAME) that would require further queries to get the ultimate answer. In other words, this utility acts as a very simplified dig.

Usage: sample-request [-t RRtype] server_address hostname

Options and Arguments:

-t RRtype

  specify the RR type of the queries. The default is the A RR.

server_address

  an IP(v4/v6) address of the recursive server to which the query is sent.

hostname

  the domain name for the query

#### sample-gai: getaddrinfo() and getnameinfo() test code

This is a test program to check getaddrinfo() and getnameinfo() behavior. It takes a host name as an argument, calls getaddrinfo() with the given host name, and calls getnameinfo() with the resulting IP addresses returned by getaddrinfo(). If the dns.conf file exists and defines a trust anchor, the underlying resolver will act as a validating resolver, and getaddrinfo()/getnameinfo() will fail with an EAI_INSECUREDATA error when DNSSEC validation fails.

Usage: sample-gai hostname

#### sample-update: a simple dynamic update client program

It accepts a single update command as a command-line argument, sends an update request message to the authoritative server, and shows the response from the server. In other words, this is a simplified nsupdate.

Usage: sample-update [options] (add|delete) "update data"

Options and Arguments:

-a auth_server

  An IP address of the authoritative server that has authority for the zone containing the update name. This should normally be the primary authoritative server that accepts dynamic updates. It can also be a secondary server that is configured to forward update requests to the primary server.

-k keyfile

  A TSIG key file to secure the update transaction. The keyfile format is the same as that for the nsupdate utility.

-p prerequisite

  A prerequisite for the update (only one prerequisite can be specified). The prerequisite format is the same as that is accepted by the nsupdate utility.

-r recursive_server

  An IP address of a recursive server that this utility will use. A recursive server may be necessary to identify the authoritative server address to which the update request is sent.

-z zonename

  The domain name of the zone that contains

(add|delete)

  Specify the type of update operation. Either "add" or "delete" must be specified.

"update data"

  Specify the data to be updated. A typical example of the data would look like "name TTL RRtype RDATA".

### Note

In practice, either -a or -r must be specified. Others can be optional; the underlying library routine tries to identify the appropriate server and the zone name for the update.

Examples: assuming the primary authoritative server of the dynamic.example.com zone has an IPv6 address 2001:db8::1234,

    $ sample-update -a sample-update -k Kxxx.+nnn+mmmm.key add "foo.dynamic.example.com 30 IN A 192.168.2.1"

adds an A RR for foo.dynamic.example.com using the given key.

    $ sample-update -a sample-update -k Kxxx.+nnn+mmmm.key delete "foo.dynamic.example.com 30 IN A"

removes all A RRs for foo.dynamic.example.com using the given key.

    $ sample-update -a sample-update -k Kxxx.+nnn+mmmm.key delete "foo.dynamic.example.com"

removes all RRs for foo.dynamic.example.com using the given key.

#### nsprobe: domain/name server checker in terms of RFC 4074

It checks a set of domains to see the name servers of the domains behave correctly in terms of RFC 4074. This is included in the set of sample programs to show how the export library can be used in a DNS-related application.

Usage: nsprobe [-d] [-v [-v...]] [-c cache_address] [input_file]

Options

-d

  run in the "debug" mode. with this option nsprobe will dump every RRs it receives.

-v

  increase verbosity of other normal log messages. This can be specified multiple times

-c cache_address

  specify an IP address of a recursive (caching) name server. nsprobe uses this server to get the NS RRset of each domain and the A and/or AAAA RRsets for the name servers. The default value is 127.0.0.1.

input_file

  a file name containing a list of domain (zone) names to be probed. when omitted the standard input will be used. Each line of the input file specifies a single domain name such as "example.com". In general this domain name must be the apex name of some DNS zone (unlike normal "host names" such as "www.example.com"). nsprobe first identifies the NS RRsets for the given domain name, and sends A and AAAA queries to these servers for some "widely used" names under the zone; specifically, adding "www" and "ftp" to the zone name.

### Library References

As of this writing, there is no formal "manual" of the libraries, except this document, header files (some of them provide pretty detailed explanations), and sample application programs.

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