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dnsupdate
dnsupdate
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Revision History
Description
Name
Date (mm/dd/yyyy)
Comments
Created
Gopakumar H.
Pillai
05/01/2001
Original – first draft
Project Home page: http://www.sourceforge.net/projects/dnsupdate
You could help me find another job, click on my name for
more details.
Table of Contents
1 Preface.. 3
2 Introduction.. 3
3 Requirements.. 3
4 Design.. 3
4.1 Dynamic Update. 4
4.2 dnsupdate. 4
5 Compilation.. 5
5.1 libnsupdate.a. 5
6 Implementation.. 5
6.1 Source Structure. 5
6.2 nsupdate. 6
6.3 dnsupdate. 6
6.4 dnsupdate.cfg. 6
6.5 Usage. 7
7 Known Issues.. 8
8 Special Notes.. 8
9 Appendix A: Default Values.. 8
10 Appendix B: Timing comparison with h2n.. 9
11 Appendix C: dnsupdate.cfg -
Configuration File.. 9
12 Appendix D: Definitions, acronyms
& abbreviations.. 11
13 Reference.. 11
1 Preface
I, Gopakumar
H. Pillai (Gopu), am dedicating the
software dnsupdate to my country,
INDIA. This project was entirely created from my home on my own time.
In search for a program that would help me create and
maintain the DNS databases, my efforts were in vain. The nearest ones I could
find were written in perl. The last thing I wanted to do from my program was to
do a "system" call. I started playing with BIND 8.2.2 P7 and
converted the nsupdate program to a function. That actually made me write the
rest of the program.
My benchmark program was the famous h2n perl script.
dnsupdate seems to be much faster than h2n. I have given a timing comparison
table between dnsupdate and h2n in Appendix B.
With my highly limited knowledge about DNS or its
configuration files (DNS tables or DNS databases) I am requesting users of this
program to pinpoint any errors or suggestions to make dnsupdate a better one.
2 Introduction
BIND is the most widely used implementation of DNS. For an
explanation of the abbreviations, please check Appendix D. The configuration
and data files to BIND named have a very complex format.
The objective was to create software that can be used with
ease without knowing the format of the
DNS tables. Also write it in a language other than scripts so that one can make
use of it by calling a function instead of executing an external program (bad
for security reasons). This also should make it faster than a script doing the
same thing. In short the objective was to create and maintain the DNS tables
(database) in an easy, fast and efficient manner.
All said one can't get away without knowing anything about
the concepts of DNS and still get it to work.
3 Requirements
The basic requirement of dnsupdate is that it should be able
to create all DNS tables from a hosts file and a configuration file and should
be able to maintain it. After creating if any changes are made to the tables
through dnsupdate, a future recreation of the tables should reflect it.
4 Design
Looking at single entry addition/deletion to the DNS tables,
dnsupdate should be using the Dynamic update feature of BIND 8 or higher as
much as possible. Since dynamic update happens over a UDP connection, it is
slow to be used for recreation of the DNS databases (tables). Recreation could
be made much faster by carefully writing directly to the files. Figure 3.1.1
illustrates the overall design of dnsupdate.
Figure 3.1.1
4.1 Dynamic
Update
dnsupdate program should use the dynamic update feature of
BIND (version 8 or higher). A request could be sent to the DNS server (named)
for adding or deleting a host or alias. The server would update its memory and
at particular intervals, it would update the DNS databases. Adding/deleting a
name server could also be done dynamically, but BIND 8 has some limitations.
Future releases supporting BIND 9 or higher should have it that way.
4.2 dnsupdate
dnsupdate should use a configuration file, so that, with the
information from the configuration file and the hosts file provided, it should
be able to recreate the DNS databases. A request for certain single entry
updations should also be added to the configuration file so that it could be
used for the next recreation of the entire databases.
Only one copy of the program should be running on the system
at any given instance. This can avoid any problems with synchronization, thus
save the databases from getting corrupted.
5 Compilation
dnsupdate is
written so that it can be used in any system running a DNS server (BIND version
8 or above).
It can be compiled
in Solaris 8 and FreeBSD 4.2. I am sure it can be compiled in a variety of
operating systems with the minimal change.
Use make utility to
compile the software. Here are the different commands one can use to compile
dnsupdate:
 "make clean" would clean all
the object files and executables.
"make" or "make
all" would compile the related libraries and source for dnsupdate.
"make nsupdatelib" would
compile nsupdate.c and create libnsupdate.a.
"make nsupdtest" would
compile nsupdate.c and create nsupdtest executable to test the nsupdate
functio.
"make Dprintf" would create
the library libDprintf.a.
"make dnsupdate" would
compile dnsupdate sources and give out dnsupdate executable. If you have already
compiled libraries, this might be the command you would want to use.
There are SYSTYPE
lines in the Makefile. Ensure that the line containing the operating system you
use should come as the last line in that bunch. For example, SYSTYPE = freebsd
line appearing as the last line that section would give compilation errors if
compiled on a Solaris system.
5.1 libnsupdate.a
To create
libnsupdate.a one needs to have the compiled code for BIND 8.2.2 P7. In the
Makefile, specify the BINDDIR as the directory containing the compiled BIND
code. If it is difficult for you to compile BIND, I have provided the libraries
for Solaris 8 and FreeBSD 4.2 with the Release 1.0.
libnsupdate.a need libbind.a and libbind_r.a to link without errors.
6 Implementation
dnsupdate has two different modes - create mode and update
mode. In create mode, it creates the DNS databases from a hosts file and the
configuration file. Create mode can be invoked with the -f option. In update
mode it adds or deletes individual entries. In update mode, it doesn't
necessarily need the configuration file, unless one wants to override the
default values.
The default configuration file is /etc/dnsupdate.cfg. One
can use an alternate configuration file with the -c option. Default values for
all parameters in dnsupdate are specified in Appendix A.
6.1
Source Structure
Table 4.1.1 describes the source files. All functions would
have a brief explanation about what it does, above their definitions in their
source files.
File Name
Description
dnsupdate.c
Main source file which parses the user parameters, checks
for another copy etc..
dnsupdate.h
Main header file which has all dnsupdate related defines
and declarations.
config.c
Contains functions to manipulate or read the configuration
file.
config.h
Configuration related defines and declarations.
processcmd.c
The brain of dnsupdate. This file has all functions, which
does the real work.
util.c
Utility functions. These are mostly used by functions in
processcmd.c
nsupdate.c
This file contains the nsupdate function, copied from BIND
source. This file has been edited and formatted.
dnsupdate.cfg
The configuration file to dnsupdate.
Table 3.1.1
Logging is done using the static library named libDprintf.a.
The library is a result of two files that are described in Table 4.1.2
File Name
Description
Dprintf.c
Source file for the logging interface.
Dprintf.h
Header file for the logging interface.
Table 4.1.2
6.2 nsupdate
The key portion of dnsupdate is the dynamic update to the
name server. BIND 8 and above supports dynamic update. I have used nsupdate.c
from the BIND distribution (BIND 8.2.2
P7) and created a nsupdate function. The nsupdate function can be used to
update a single line of command or to update from a file specified.
Usage:
nsupdate(
cmd, flag);
flag - if TRUE (other than 0) cmd should be a
filename with the update strings
else
cmd should be a single string (with or
without trailing newline).
If TEST_UPDATE is defined, nsupdate can be tested as a
standalone program.
6.3 dnsupdate
dnsupdate, when executed, checks for another copy of itself
running. This checking is done using a semaphore with the key 492743 (0x784c7).
If another copy is found, in create mode (-f option), dnsupdate would wait
until other program exits. In update mode it would exit immediately, but can be
made to wait with the -w option.
Then it reads the configuration file and checks whether
named is running or not. In case of a failure the program exits immediately.
In create mode, updates are written to the DNS databases
directly. In update mode, adding/deleting hosts and aliases (CNAME) are done
using dynamic update. Rest all is directly written to databases.
All direct writings are done on temporary files in the same
directory as the file being worked on. Then the temporary file is moved to the
original file.
In create mode, dnsupdate restarts named, since the dynamic
update cannot be triggered on with a HUP signal. But in update mode a HUP
signal is sent to named after updating the databases, so that, named can
re-read the DNS tables. If the update is only for a host or alias no signals
are sent to named.
In create mode, dnsupdate creates /etc/resolv.conf file too.
It overwrites the existing /etc/resolv.conf file.
In update mode, dnsupdate adds the requested information to
the configuration file so that it can be used for the next run with -f option.
It adds or deletes the NETWORK, NAMESERVER and ALIAS lines dynamically.
6.4 dnsupdate.cfg
/etc/dnsupdate.cfg is the default configuration file used by
dnsupdate. It could be overridden with the -c option. Appendix C displays a
copy of the configuration file. Here is an explanation of all fields that can
be found in the cfg file:
Key
Description
DOMAIN
The domain name. If not specified it would read from
/etc/defaultdomain file.
DNSDIR
Directory where DNS databases reside. Default is
/var/named in case of Solaris and /etc/namedb for FreeBSD.
NAMEDCONF
Full path name of named.conf file. If not specified
DNSDIR/named.conf would be used.
LOGFILE
Full path name of the log file. Default is /tmp/dnsupdate.log.
LOGLEVEL
Log level. 0 = None. 1 = Minimum. 9 = Maximum.
NETWORK
Network addresses. Format is NetworkAddress:Netmask. e.g. 166.117.12:255.255.255.0
NAMESERVER
Additional name servers. Format is NameServerHostName:NameServerIPAddress. e.g. ns1.gopu.com:192.168.0.1
CONTACT
Contact address to be added to the DNS databases. Default
is root.DOMAIN, where DOMAIN is the domain name.
NAMEDPID
Full path of the named PID file. Default is /etc/named.pid
in case of Solaris and /var/run/named.pid in case of FreeBSD.
NAMEDEXE
Full path of the named executable. Default is
/usr/sbin/named in case of FreeBSD and /usr/sbin/in.named in case of Solaris.
HOSTSFILE
Hosts file to create the DNS databases from. Default is
/etc/hosts
ALIAS
Alias name for an existing host. Fomat is AliasName:HostName. e.g. www:gopu.com
Comment lines start with a #
character.
Blank lines are ignored.
File follows a format of KEY=VALUE
There should not be any spaces before
or after the = sign.
NETWORK, NAMESERVER and ALIAS key-value
pairs are updated dynamically by dnsupdate.
6.5 Usage
dnsupdate <-a|-d> -n HostName -i IPAddress
dnsupdate <-a|-d> -z ForwardZone
dnsupdate <-a|-d> -r ReverseZone(NetworkAddress)
-mNetMask
dnsupdate <-a|-d> -s NameServer -i IPAddressOfServer
dnsupdate <-a|-d> -p AliasName(CNAME) -n HostName
dnsupdate -f
dnsupdate -h
Additional options:
[-c
ConfigFile] [-w]
Defaults:
Config
File: /usr/hb/cfg/dnsupdate.cfg
DNS
Directory: /var/named
Log File:
/usr/hb/log/dnsupdate.log
Example:
dnsupdate -h
displays this
help screen
dnsupdate -a -n foo -i 192.168.0.1
Add the
host specified to the DNS table.
dnsupdate -d -i 192.168.0.1 -n foo -w
Delete the
host specified from the DNS table.
But wait
until any running dnsupdate exits instead of
quitting
immediately.
dnsupdate -a -z gopu.com
Add the
forward lookup zone, gopu.com.
dnsupdate -a -r 192.168.5 -m 255.255.255.0
Add the
reverse zone 5.168.192.in-addr.arpa
dnsupdate -a -s ns1.gopu.com -i 192.168.0.1
Add the
name server ns1.gopu.com
dnsupdate -a -p www.gopu.com -n gopu.com
Add the
alias name (CNAME) www.gopu.com for gopu.com
dnsupdate -f
Recreate
the whole DNS database from the hosts file
and the
default configuration file.
Note:
1. DO NOT
specify network address for a reverse lookup
in reverse order.
2. If
specified -f option the program waits for any running
dnsupdate to exit. Without the -f option
the program would exit
saying "Another copy running".
This can be overridden with
with the -w option, which will force the
program to wait
7 Known
Issues
Does not roll back the DNS databases
to its previous good state in case of a failure. As a work around, a script can
do this work. If dnsupdate returns a non-zero value, then the database needs to
be restored.
dnsupdate can support only one domain.
Normally named expects the named.conf
file to be in /etc. But FreeBSD creates a symbolic link from /etc/named.conf to
/etc/namedb/named.conf. So it solves the problem. Solaris does not. One has to
do it manually or copy the file from /var/named each time it is modified.
dnsupdate, in update mode, does not
add host details to the configuration file. So the hosts information should be
maintained external to dnsupdate or a script could create a hosts file from the
DNS databases.
8 Special
Notes
For the first time one needs to run
dnsupdate -f so that things are in place for a dynamic update.
To force writing the updated
information, one can send the TERM signal to named. Don't forget to restart
named after that.
To compile dnsupdate, one should get
the source code for BIND 8.2.2 P7 and compile it first. Then edit the Makefile
to specify the BIND dir. Alternatively, use the already compiled libraries
found on the project home
page.
Ideally Name servers could have been
added dynamically. BIND 8 has some restrictions, so it adds/deletes only the
first nameserver. But BIND 9 seems to support adding name servers dynamically.
Currently dnsupdate directly write to the DNS database and later versions
supporting BIND 9 can do it dynamically.
In nsupdate.c some variables have been
moved to global variable section, since stack based arrays were failing.
While processing the hosts file with
-f option, dnsupdate processes alias names (names from the third column in the
hosts file) too and treats them as though they are valid host names. So an MX
record is also added for each entry. Probably it would have been right to
consider them as aliases.
9 Appendix
A: Default Values
KEY/Description
FreeBSD
Solaris
Configuration File
/etc/dnsupdate.cfg
/etc/dnsupdate.cfg
DOMAIN
contents of /etc/defaultdomain
contents of /etc/defaultdomain
DNSDIR
/etc/namedb
/var/named
NAMEDCONF
$DNSDIR/named.conf
$DNSDIR/named.conf
LOGFILE
/tmp/dnsupdate.log
/tmp/dnsupdate.log
LOGLEVEL
MAX (9)
MAX (9)
CONTACT
root.$DOMAIN
root.$DOMAIN
NAMEDPID
/var/run/named.pid
/etc/named.pid
NAMEDEXE
/usr/sbin/named
/usr/sbin/in.named
HOSTSFILE
/etc/hosts
/etc/hosts
Semaphore Key
492743 (0x784c7)
492743 (0x784c7)
10
Appendix B: Timing comparison with h2n
Number of hosts
dnsupdate -f
h2n
100
0.132s
0.113s
1,000
0.300s
0.439s
5,000
0.862s
2.244s
10,000
1.626s
6.552s
50,000
7.807s
4m20.457s
Benchmark was done on a Sun Sparc system running Solaris 8,
Perl 5.005_3 and h2n 1.29.
11
Appendix C: dnsupdate.cfg - Configuration File
# Configuration file for dnsupdate
# This is a comment, blank lines are ok.
# Your domain name. Only 1 DOMAIN line is allowed. If not
specified
# /etc/defaultdomain would be read.
#DOMAIN=gopu.com
# named.conf file to be used. This is a must. Only one
line is allowed.
# If not specified /var/named/named.conf would be used in
case of Solaris
# systems or /etc/namedb/named.conf would be used in case
of FreeBSD.
#NAMEDCONF=/var/named/named.conf
# DNS Directory. If not specified /var/named would be
used in Solaris.
# /etc/namedb in FreeBSD. Only one such line is
permitted.
#DNSDIR=/var/named
# Log file. If not specified /tmp/dnsupdate.log would be
used. Only
# one line is allowed.
#LOGFILE=/users/gopu/dnsupdate/dnsupdate.log
# Log Level - NONE=0, MIN=1, MED=5, MAX=9. If not
specified
# MED=5 would be used. Only one such line is allowed.
LOGLEVEL=9
# named.pid file. If not specified /var/run/named.pid
would be used
# in FreeBSD systems and /etc/named.pid would be used in
Solaris.
# Only one such line is permitted.
#NAMEDPID=/etc/named.pid
# named executable path. This is used to restart named.
# If not specified /usr/sbin/named would be used in
FreeBSD systems and
# /usr/sbin/in.named would be used in Solaris systems.
# named restarts are done with -f option, to enable the
dynamic
# update
NAMEDEXE=/usr/sbin/in.named
# Hosts file to read for -f option. If not specified,
/etc/hosts file
# would be used. Only one such line is allowed.
HOSTSFILE=/tmp/hosts
# NETWORK : Network without the trailing zeros.
# Format NET:SUBNETMASK
# More than one line is allowed.
# These entries are dynamically updated by dnsupdate,
hence would
# be moved to the bottom of the file.
NETWORK=192.168.2:255.255.255.0
NETWORK=10.1:255.255.0.0
# ALIAS - Alias for an existing host. Also known as CNAME
record.
# Format: ALIASNAME:HOSTNAME
# Multiple lines are allowed.
# These entries are dynamically updated by dnsupdate,
hence would
# be moved to the bottom of the file.
ALIAS=www:gopu.com
# NAMESERVER - Name server in each domain's NS records.
No expansion
# of names would be done if a trailing dot is present. A
colon separated
# IP address must be provided for each server.
# Format: HOSTNAME:IPADDRESS
# More than one line is allowed.
# These entries are dynamically updated by dnsupdate,
hence would
# be moved to the bottom of the file.
NAMESERVER=ns1.gopu.com.:192.168.0.1
NAMESERVER=ns2:10.1.0.2
# CONTACT - Name or email address of the contact person
in the SOA
# mail address. Default is root.DOMAIN. Only one line is
allowed.
# If not specified, root.$DOMAIN would be used.
#CONTACT=root.gopu.com
12
Appendix D:
Definitions, acronyms & abbreviations
DNS
Domain Name Service. The service which provides the IP
address of a host given its name and vice-versa.
Name Server
DNS.
BIND
Berkeley Internet Name Domain. This is an implementation
of DNS, a public domain software, which is used by almost all of the domain
name servers around the world.
hosts file
/etc/hosts file. It contains the names of hosts and their
IP addresses.
h2n
a public domain perl script which can be used to create
the DNS databases (tables) from a hosts file.
named
DNS server executable
in.named
In solaris the name server is named in.named.
IP
Internet Protocol. The whole Internet communicates using
this network protocol.
UDP
Unified Datagram Protocol. A connectionless protocol built
over IP.
TCP/IP
Trasmission Control Protocol / Internet Protocol. The most
common protocol used on the Internet.
IP Address
The addressing scheme used by systems on the Internet to
communicate each other. It is of the form n.n.n.n where n could range from 0
to 255 (certain restrictions apply).
/etc/resolv.conf
The file which tells the system where the DNS is, so that
a name like dnsupdate.sourceforge.net could be translated to its IP address.
13
Reference
Description
Author
Publication
ISBN
http://sourceforge.net/projects/dnsupdate
Project Home Page with downloads
http://dnsupdate.sourceforge.net
Project Web Page
http://www.dns.net/dnsrd
DNS Resources Directory
DNS and BIND, 3rd edition
Paul Albitz, Cricket Liu, Mike Loukides
O'REILLY
1-56592-512-2
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