A Perl script to rewrite the “static” IP address in the FreePBX Asterisk SIP Settings when it is changed by your ISP

August 1, 2011 at 9:58 pm · Filed under Asterisk, Linux, networking, VoIP

This post is going to be a bit long because I first need to explain the “why” behind this script, then how to obtain the prerequisite Perl modules, then the script itself and how to test it after installation.

If you are using a recent version of Asterisk and FreePBX you may be using the Asterisk SIP Settings module (under the “Tools” tab) to automatically set various SIP parameters.  This module is a great help to those who don’t know what they are doing, but there is a trap for the unwary (and in this case it’s NOT the fault of FreePBX – it’s a longstanding bug in Asterisk that’s the problem).

At the top of the Asterisk SIP Settings configuration page, in the NAT Settings section, there are two options that can be set.  The first is NAT and there are four possible choices:

• yes = Always ignore info and assume NAT
• no = Use NAT mode only according to RFC3581
• never = Never attempt NAT mode or RFC3581
• route = Assume NAT, don’t send rport

In theory, if you have a fixed IP address AND your Asterisk server is not behind an external router that does NAT translation, you should use “no” (and most of the rest of this article will not be relevant to you).  This article is intended more for home and SOHO users that both have their Asterisk server behind a hardware router of some kind, and that get their broadband service from a company that occasionally changes their IP address without warning.  For such users, the preferred setting is “yes”.  I’m not enough of a networking guru to tell you under what circumstances one of the other settings might be appropriate (if you understand this stuff, feel free to leave a comment and enlighten us).

FreePBX: Asterisk SIP Settings page, NAT Settings (Public IP Option)

It’s the next set of settings that can get us into trouble.  This is the IP Configuration and there are three possible choices:

• Public IP
• Static IP
• Dynamic IP

If your IP address never changes AND you aren’t behind a hardware firewall then you can usually just set this to “Public IP” and let it go at that.  You will not be asked to fill in any other values.  But most users that are not in that situation will pick one of the other two choices, and this is where the problem arises.  Conventional wisdom has it that if your ISP ever changes your IP address without advance warning (which is the case for most cable broadband and DSL users), you should use the Dynamic IP setting.  In this case there is an auto-configure button that will fill out the fields for you, although you may need to fill in the Dynamic Host field yourself.  This is the “External FQDN as seen on the WAN side of the router and updated dynamically, e.g. mydomain.dyndns.com” (as explained if you mouse over the words “Dynamic Host”).  You can use a DynDNS address (or an address from a similar service) or an address you have purchased.  But the problem is that for some users, THIS METHOD SIMPLY DOES NOT WORK.

FreePBX: Asterisk SIP Settings page, NAT Settings (Dynamic IP Option)

If you try to use Dynamic IP and it won’t work for you, what happens is you will get all sorts of weird errors.  You may get one way audio, some calls may disconnect for no apparent reason after about five seconds, and you will see other weird errors in your CLI.  If you change this setting to “Static IP” and click the auto-configure button and then submit the changes, the problems magically go away – UNTIL your ISP changes your IP address, at which point you suddenly have no connectivity to the outside world.  If you ask for help, everybody and their brother will tell you to use the Dynamic IP setting, and the minute you try that you’ll get all the weird errors again.

FreePBX: Asterisk SIP Settings page, NAT Settings (Static IP Option)

So if that’s your situation, you need this Perl script.  Coupled with a cron job, it goes out and checks your IP address every five minutes and if it notices it has changed, it changes it in the MySQL database (same as if you entered it into the External IP text box on the Asterisk SIP Settings configuration page) and then reloads Asterisk.  Therefore, you can use the Static IP method and it hopefully it will work reliably.  If and when your IP address changes, you should only be down for about five to ten minutes at most (hopefully your broadband provider usually does such changes in the middle of the night!).

Prerequisites:

You still have to use a Dynamic DNS service to keep track of your IP address if you want external extensions to be able to find your server on the Internet.  It’s not required for this script to work, though, so I won’t say any more about that except to note that if you use a recent vintage hardware router, it probably has DDNS support built in.

You may have to install some Perl modules on your system.  This script uses three: WWW::Mechanize, Data::Validate::IP, and Mysql.  There are typically two ways to install any missing Perl modules on your system.  One is to do this from the Linux command prompt:

perl -MCPAN -e shell

This will put you into a Perl CPAN shell and if it’s the very first time you’ve ever run this, it may ask you to do some configuration first.  Go ahead and do it.  If you don’t know how to answer a particular question, accepting the default is usually a pretty safe bet (if you disagree with me on this, then you know enough to know how to answer the questions, so you don’t need my help). However there are a couple questions related to buffers where you have the option to not create one, and I usually don’t because I don’t spend much time in the Perl shell.  Just read the questions and either use the default answer, or another suggested answer that fits your preferences.  When it comes time to pick servers (from which you will download modules), just pick two or three that are close to you.

After you’ve done the configuration, just install each module (if you already have it, it may say “nothing to do” and stop).  Alternately, if you configured Perl to ask before downloading dependencies, you may need to answer “yes” a few times to allow dependencies to be downloaded and installed. To install the required modules from within the CPAN shell, just do these, one at a time:

install WWW::Mechanize
install Data::Validate::IP
install Mysql   (you probably already have this anyway).

To quit the CPAN shell, just type quit and press Enter.

Alternately, in some distributions you can get certain Perl modules from the distribution’s repository.  For example, in Centos you may be able to use:

yum install perl-WWW-Mechanize.noarch
yum install perl-Data-Validate-IP.noarch

It’s likely you already have the Mysql module. Depending on your distro you may have to leave off the .noarch, or find a specific version in an appropriate repository.  Installing from the CPAN shell make take a bit more time for the initial configuration, but you will always get the correct version of the module.

Note that if you use Webmin, there is a third way – you can install modules from the Other | Perl Modules | Install Module page.  BUT, that may not work correctly until you have configured CPAN as mentioned above.  Don’t let that stop you from trying it, though!

The Script:

Here is the Perl script.  Note that as always, it WILL overflow the lines in WordPress, so you will want to cut and paste into a text editor.  Also note that WordPress MAY change apostrophes and quotes into “prettified” versions, and if it does that will totally mess up Perl.  I’m going to put this in a preformatted text block so hopefully WordPress won’t change anything (it doesn’t appear that it has), but you never know.  One final note, don’t confuse backticks (`) with apostrophes (‘) – backticks are used to run a command that would normally be run from a Linux command prompt.

#!/usr/bin/perl

# This program gets the current IP address (as assigned by the ISP) from
# http://hipbx.org/myip.php and modifies the FreePBX Asterisk SIP settings if the
# external IP address has changed. Invoke it as cron job that runs every 5 minutes.

use strict;
use warnings;
use WWW::Mechanize;
use Data::Validate::IP qw(is_public_ipv4);

# GET CURRENT IP ADDRESS
my $mech = WWW::Mechanize->new( autocheck => 1 );

# NOTE THE http QUERY IN THE NEXT LINE - PLEASE PASTE THIS INTO YOUR WEB
# BROWSER AND MAKE SURE IT RETURNS YOUR IP ADDRESS AND NOTHING ELSE.
$mech->get('http://hipbx.org/myip.php');
$mech->success or die 'Cannot connect to http://hipbx.org/myip.php';
my ($ip) = ($mech->content() =~ /(\d+\.\d+\.\d+\.\d+)/);

# VALIDATE RESULT RECEIVED

if (is_public_ipv4($ip)) {

    # SET UP TO CONNECT TO MySQL DATABASE
	use Mysql;

	# MYSQL CONFIG VARIABLES
	my $host = "localhost";
	my $database = "asterisk";
	my $tablename = "sipsettings";
	my $keyword = "externip_val";
	my $user = "freepbxuser";
	my $pw = "password";

	# PERL MYSQL CONNECT()
	my $connect = Mysql->connect($host, $database, $user, $pw);

	# SELECT DB
	$connect->selectdb($database);

	# DEFINE A MySQL QUERY
	my $myquery = "SELECT data FROM $tablename WHERE keyword like '$keyword'";

	# EXECUTE THE QUERY FUNCTION
	my $execute = $connect->query($myquery);

	# FETCHROW SINGLE RESULT
	my $externip = $execute->fetchrow();

	# COMPARE IP ADDRESSES

	if ($externip ne $ip) {
		
		# IP HAS CHANGED SO UPDATE IP ADDRESS IN DATABASE
		
		$myquery = "UPDATE $tablename SET data = '$ip' WHERE keyword = '$keyword'";
		$execute = $connect->query($myquery);

		# WRITE CONFIG FILES AND RELOAD ASTERISK
		`/var/lib/asterisk/bin/module_admin reload`;

		# OPTIONAL SEND EMAIL TO SYSTEM ADMINISTRATOR(S)

		# my $mailstring = 'echo "This is an automated message - please do not reply. Either we had a power or Internet outage (in which case there is a slight chance you may receive this message even if our IP address is unchanged), or our Internet Service Provider has changed the IP address of our phone server to ' . $ip . '" | mail -s "ISP may have changed our IP address" someaddress@gmail.com,anotheraddress@somewhere.com';
		# system($mailstring);
	};
};

NOTES on the above script, including THINGS YOU MUST CHANGE:

Note that the script uses the address http://hipbx.org/myip.php to check for your IP address. Click on that link and make sure you get the expected result — it should show your external IP address and nothing else. I originally used a different service (at http://automation.whatismyip.com/n09230945.asp) but it’s had a pattern of changing URL’s without warning, and Rob Thomas has graciously offered this alternative, which he says will “be there forever.” If for some reason he’s wrong about that, and you find it no longer works, you’ll need to find another source that returns your IP address, and ONLY your IP address, with no extraneous HTML formatting or text (another one I’ve discovered is http://icanhazip.com/).

Under the MYSQL CONFIG VARIABLES, note the two variables $user and $pw. These must be changed to the correct values for YOUR system. You will usually find these in one of two places. You can look in /etc/amportal.conf and look for the variables AMPDBUSER and AMPDBPASS — these will usually be near the bottom of the file in newer installs, in a “— CATEGORY: Bootstrapped or Legacy Settings —” section, but they can be anywhere in the file.

Another place they may be found is in the file /etc/freepbx.conf — in that file, look for lines similar to:

$amp_conf['AMPDBUSER'] = ‘freepbxuser’;
$amp_conf['AMPDBPASS'] = ‘password’;

Those will give you the values to insert into the $user and $pw variables in the script. YOU MUST INSERT THE CORRECT VALUES OR THE SCRIPT WILL NOT WORK! By the way, if you have both of the above-mentioned files, make sure that the AMPDBUSER and AMPDBPASS variables are set to the same respective values in both files, otherwise your CDR Reports page may not work.

Finally, if you want an e-mail notification when your IP address has changed, uncomment the two lines under “# OPTIONAL SEND EMAIL TO SYSTEM ADMINISTRATOR(S)” and modify the first line appropriately (make sure you use one or more valid e-mail addresses!). BE CAREFUL NOT TO DELETE THE TRAILING APOSTROPHE (just before the semicolon). Yeah, I did that once.

Save your script to either the /root directory or the /var/lib/asterisk/agi-bin (or another location of your choosing). I named it checkip.pl, solely because that was the name of a previous script I had run and I had already created a cron job for it. You must make the script executable, for example:

chmod u+rx /var/lib/asterisk/agi-bin/checkip.pl

Of course you will specify the correct filename and directory. Now it’s time to test the script. From the Linux command prompt, navigate to the directory where you stored the script:

cd /var/lib/asterisk/agi-bin

Now run the script from the command prompt:

./checkip.pl

Hopefully you won’t see any error messages. Remember it’s going out to do a web query to get your external IP address, so don’t get concerned if it takes a second or two. If you had an incorrect address stored in your FreePBX Asterisk SIP Settings configuration, it will take longer because it will restart Asterisk (so, you may not want to test this at a time when there are likely to be active calls on your system).

Usually if you do see errors they will fall into one of two categories. The first is a missing Perl module, which you will need to obtain as described above. The second is a syntax error, which you should not get if you cut and pasted the script, and made the changes noted above. If you get a permissions error, you probably forgot to make the script executable!

Setting up a cron job:

Once it runs without errors, you will want to create a cron job so it runs automatically every five minutes. Do NOT run it more often than that, or the lookup service may ban your IP address, and you don’t want that to happen (whatismyip.com would do that, which is another reason not to use them), and besides, it’s not polite to hog the resources of someone else’s server! And if you are running it on multiple servers at the same IP address, then adjust the polling speed so that the total polling from all servers doesn’t exceed once every five minutes. An occasional additional test is probably not an issue, but if you try to poll every minute you just might get banned!

The usual way to add a cron job is to run this command:

crontab -e

(If you’re not currently running as root use sudo crontab -e instead)

This will open a text editor showing your current cron jobs. Just add a new line to the bottom of the file with your new cron job. To run the script every five minutes, you could use something like this:

*/5 * * * * /var/lib/asterisk/agi-bin/checkip.pl

Or to be more specific as to when the script runs (this will run it exactly on the hour, at five minutes after the hour, at ten minutes after the hour, and so on):

0,5,10,15,20,25,30,35,40,45,50,55 * * * * /var/lib/asterisk/agi-bin/checkip.pl

Just save the changed file when you are finished. The alternate method is to use Webmin’s System | Scheduled Cron Jobs module to set up your cron job.

Final testing:

The easiest way to test to make sure this is all working is to wait until a time that there are no active calls on the system, then go to the Asterisk SIP Settings configuration page and change the External IP address to something invalid (just change the last digit of the current address and Submit Changes, then do the usual orange bar reload). On the next five minute interval, the script should detect that the external IP address doesn’t match the one stored in the database, and it will write the correct value to the database and reload Asterisk. If you watch the Asterisk CLI during this time, you should actually see the reload take place. After that, if you go back to the Asterisk SIP Settings configuration page, the correct IP address should be there. To be extra safe, you should also view the contents of the file /etc/asterisk/sip_general_additional.conf and make sure that the externip= line shows the correct IP address.

Now you don’t have to worry about frantic calls from users at inopportune times because your ISP changed your IP address and none of the phones are working, and you also won’t have any of the problems associated with the Dynamic IP method!

I want to thank Moshe Brevda for giving me the information I needed to do the MySQL database write, after a particularly frustrating middle of the night session (not helped by bumping into a truly arrogant bastard on an IRC channel), and also for one correction to this article (see my comment in the comments section below). If any “Perl purists” are reading this and you want to offer a constructive comment without giving me any attitude, I’m fine with that. But if you are like some of your I-know-it-all-and-your-coding-sucks brethren in the IRC channel, don’t even waste your time posting a comment, because I won’t approve it. No, you really DON’T need to use any other Perl database modules to do this simple task, and no, I DON’T want to learn your philosophy of writing Perl code.

NOTE: If you have been using an etc/asterisk/sip_nat.conf file, be sure to remove it completely – you don’t need it anymore! And as usual, there are no warranties — we’re experimenters here, and sometimes we don’t catch all the bugs, especially on the first go around! However, I would assume that anyone who is running a “professional” installation would pay their ISP for a true static IP address (one that never changes), and therefore wouldn’t need this script in the first place.

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