Maintaining DNS Sanity with Hawk

Greg Heim

If you are a DNS administrator for anything more than a few dozen hosts, it’s easy for your database to get out of sync with what’s really on your network. The GPL software tool, Hawk, is designed to help administrators track which hosts in DNS are really on your network and, just as importantly, which hosts are on your network but not in DNS. Hawk can help take the mystery out of DNS maintenance, resulting in a much cleaner, up-to-date database.

Hawk consists of three components: a monitor written in Perl, a MySQL database backend, and a PHP Web interface. The monitor periodically checks whether hosts on your network appear in DNS and are answering on your network. It checks for existence on the network by way of an ICMP ping. I mention ICMP because by default, the Perl Net::Ping module “pings” by attempting a UDP connection to a host’s echo port. With the various types of hosts possible on a typical network, this is probably not desirable. As each IP address on your network is polled, the monitor records or updates in the database the current IP address and the hostname, if one exists. If the ping is successful, this timestamp is also recorded in the database.

The Hawk interface consists of a Web page that allows you to choose which “network” to view and how to sort the results. You can also choose whether to view addresses that are neither in DNS nor have responded to pings. These are typically uninteresting, so by default they are not displayed. Each host displayed on the page has a hostname (if available), a last ping time, and a colored “LED” indicating the current status of the address. The LED color will indicate one of five states:

Green — Address exists in DNS, and is currently answering pings.
Yellow — Address exists in DNS, but has not answered in more than 24 hours (configurable).
Red — Address exists in DNS, but has not answered in more than 1 week (configurable).
Blue — Address does not exist in DNS, however it is answering pings. This could indicate an unauthorized use of an address, or it could indicate something such as a DHCP — assigned address that has no DNS entry.
Purple — Address does not exist in DNS, and does not answer pings. This is generally uninteresting to us, so by default these hosts are not displayed. See Figure 1.

Installation

Perl

As previously mentioned, Hawk has three components. These components may each be hosted on separate machines or the same machine, depending on your environment. The monitor should run happily with any version of Perl 5. But the following additional modules will need to be installed: Net::Netmask, Net::Ping, DBI, and DBD::mysql. You can install these modules as follows:

# perl -MCPAN -e "install Net::Netmask"
# perl -MCPAN -e "install Net::Ping"
# perl -MCPAN -e "install DBI"
# perl -MCPAN -e "install DBD::mysql"

The database used for storing Hawk’s data is MySQL. Hawk was originally written using MySQL 3.23, but since the database requirements are minimal, you can probably get away with older versions, and certainly newer ones. Before the Perl backend and PHP frontend can communicate with the database, you must create the appropriate database and table to store the data. Next, you need to create a database user to allow read and write access to the data from the scripts. Connect to the database as follows:

# mysql --user=<mysql admin user> --password --host=<mysql server>
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 8 to server version: 3.23.40-log

Type 'help;' or '\h' for help. Type '\c' to clear the buffer.

mysql>

create database hawk;
use hawk;
create table ip (
   ip char(16) NOT NULL default '0',
   hostname char(255) default NULL,
   lastping int(10) default NULL,
   primary key  (ip),
   unique key ip (ip),
   key ip_2 (ip)
) type=MyISAM comment='Table for last ping time of hosts';

grant select,insert,update,delete
     on hawk.*
     to hawk@localhost
     identified by 'hawk';
grant select,insert,update,delete
     on hawk.*
     to hawk@"%"
     identified by 'hawk';
flush privileges;

For managing MySQL, you may want to consider installing phpMyAdmin, which is available from:

http://www.phpmyadmin.net

Apache/PHP

The interface was written using PHP 4.0.6 under Apache 1.3.22. Later versions of PHP should work fine, and any version of Apache will probably work. If your Web server is running on the same machine as the Hawk monitor, you can simply make a symbolic link in the Apache document root to the PHP directory of hawk as follows:

# cd /var/apache/htdocs
# ln -s /opt/hawk/php hawk

Hawk

Hawk is hosted at SourceForge. To download, go to:

http://sourceforge.net/projects/iphawk

ftp://ftp.sourceforge.net/pub/sourceforge/iphawk

# cd /opt
# tar xvzf hawk-0.6.tar.gz
# ln -s /opt/hawk-0.6 /opt/hawk

./daemon                 - directory for perl monitor daemon
./daemon/hawk            - the monitor daemon
./daemon/hawk.conf       - config file for monitor daemon
./php                    - directory for php interface
./php/hawk.conf.inc      - php web interface config file
./php/hawk.css           - style sheet file for web interface
./php/hawk.php           - web interface script
./php/images             - directory for web interface images

@networks — This should contain a list of local networks you want to be monitored by Hawk. The networks must be specified in CIDR format. That is, if you have a class C network (24 bits) of the range 192.168.2.0-255, the CIDR form would be “192.168.2.0/24.”

@gateways — This should contain the list of gateways used by all networks. This parameter is not required, however if it is used, the monitor will verify that the gateway is up before trying the rest of the hosts on that network.

$frequency — This parameter is the number of seconds between checks. A 0 value will cause the monitor to loop continuously.

$pingtimeout — This variable indicates how long a ping will wait before giving up and moving on to the next host.

$debuglevel — This can be set at 0-2. During initial setup, you may want to use debug level 2. This will allow you to see every ping, and verify database operations. Level 1 will give basic progress reports (e.g., when each network is being checked). Level 0 is, of course, no logging at all. You probably want to switch to level 1 or 0 after initial install.

$logfile — The name of the logfile where the above debugging information is written.

$dbuser: mysql database username
$dbpass: mysql database password
$dbhost: database server hostname or ip address
$dbname: database name ("hawk")

$pidfile: pid file used for shutting down and restarting hawk.

The PHP backend has a similar simple configuration. The config file is php/hawk.conf.inc. This file is sourced into the main hawk.php script so, like the monitor config file, it must contain syntax understood by PHP. The configurable parameters are as follows:

$dbuser, $dbpass, $dbhost, $dbname — Should be set to the same as above.

$redzone — If a host has not been ping-able in this amount of time (in seconds), the LED will glow red.

$yellowzone — If a host has not been ping-able in this amount of time (in seconds), the LED will glow yellow, unless it has also surpassed $redzone.

$networks — This should contain all the networks you specified within your hawk.conf file above. However, each of the networks is paired with a human-readable name for this parameter. If your network contains a really large broadcast domain, it may be too large for easy viewing on a single Web page, in which case you can break it into logical pieces. You can do so by specifying smaller, adjacent networks. For example, if you specified 192.168.4.0/22 in your daemon/hawk.conf above, you can break that into the following networks in php/hawk.conf.inc for display purposes: 192.168.4.0/24, 192.168.5.0/24, 192.168.6.0/24, 192.168.7.0/24. See hawk.conf.inc.sample (Listing 2).

The look and feel of the Web interface for Hawk are customizable using cascading style sheets. All of the styles have been placed into a separate CSS file, php/hawk.css.

Running Hawk

After installation of all components is complete, the next step is to start Hawk by hand and watch the logfile to verify proper operation:

# /opt/hawk-0.6/daemon/hawk &
# tail -f /var/log/hawk

Once proper operation is verified above, configure your system to start Hawk at boot. Below is a sample init.d script that can be used for starting/stopping/restarting Hawk. See hawk.init.d.sample (Listing 3).

You will need to copy the script into your init.d directory and make symbolic links to the appropriate rc?.d directories as follows:

For the 0, 1, S, and 6, runlevels:

ln -s /etc/init.d/hawk /etc/rc0.d/K90hawk
ln -s /etc/init.d/hawk /etc/rc1.d/K90hawk
ln -s /etc/init.d/hawk /etc/rc6.d/K90hawk
ln -s /etc/init.d/hawk /etc/rcS.d/K90hawk

ln -s /etc/init.d/hawk /etc/rc2.d/S90hawk
ln -s /etc/init.d/hawk /etc/rc3.d/S90hawk
ln -s /etc/init.d/hawk /etc/rc4.d/S90hawk

Once you’ve verified proper operation of Hawk and installed the above startup scripts, reboot your system at the next opportunity to verify proper startup.

Next, you need to verify the interface is working properly by opening the page in your browser. The URL should be something like http://hawk.someplace.org/hawk/hawk.php. When the page loads, select a network and click “Go”. The page will be redisplayed listing the hosts on your network as in Figure 1. If this does not work as expected, database connectivity is most likely the problem. PHP will generally report any connectivity problems directly on the Web page. The error messages given are usually very specific and you should be able to identify the problem right away. You should also check your MySQL log to verify the PHP queries are actually reaching the database.

If you were successful with your installation, you will be able to use Hawk to manage your DNS with a little more sanity.

Greg Heim has been working as a UNIX systems administrator for 13 years. He has a strong background in programming and relational databases. He can be contacted at: gregheim@mindspring.com.