[TriLUG] Strategies for dynamic-IP machines

[Greg Brown]

I have a script that does this.  The script lives in /home/greg/scripts and 
it depends on the file ip-eth1 which is created by the script (it also reads 
the e-mail addresses in from a file called ip-list (I know, poorly named).  
The ip-list file contains one e-mail address per line.  I run the script, 
ip-watch, from cron every 30 minutes (crontab runs as root for no good 
reason).  The following is my cron entry followed by the perl script.  Hope 
this helps!

Cron:
00,30 * * * * /home/greg/scripts/ip-watch 2>/dev/null 

the ip-watch script:

#!/usr/bin/perl

#######################################################
#
# watches eth1 to see if the IP address changes
#
# Greg Brown
# gregbrown at mindspring.com
# Sat Feb 16 22:56:47 EST 2002
#
#######################################################

# first read in the ip address in the current file
open(CURRENTIP, "/home/greg/scripts/ip-eth1");

foreach $line (<CURRENTIP>) {

        chomp($line); # get rid of the newline
        $currentIP=$line;

}

close(CURRENTIP);

# now that we know what the IP address was the last time the script ran
# let's see what it is now to see if it changed
open(CHECKIP, "/sbin/ifconfig eth1 |");

foreach $ipLine (<CHECKIP>) {

        # now sort through this crap until we find the IP address
        chomp($ipLine);  # get rid of the newline

        if ($ipLine =~ m/\binet addr\b/) {

                $ipLine=~ s/\s+/ /g; # get rid of the extra spaces

                @ipLineLong=split(/\s/,$ipLine); # split at the space
                # at this point the ip address is stored in
                # $ipLineLong[2]

                # print "$ipLineLong[2]\n";

                $ipInfo=$ipLineLong[2];

                @ipInfo=split(/\:/,$ipInfo);

                # the current IP address is now stored in $ipInfo[1]

                # now check the two IPs aginst each other

                # print "$ipInfo[1] $currentIP\n";

        } # end the if inet addr

} #end the foreach loop

# now we have the old IP address ($currentIP) and the new IP Address
# (ipInfo[1]) so let's compare them to see if they are the same

if ($ipInfo[1] eq $currentIP) {

        # print "we are the same $ipInfo[1] $currentIP\n";

}

else {

        # print "We are NOT the same: $ipInfo[1] $currentIP\n";

        # if we are here then it can be said that the IP Addresses
        # are not the same so we'll have to notify everyone that the
        # IP Address has changed

        # first open the list containg the people to mail
        open(MAILLIST, "/home/greg/scripts/ip-list");

        # now process the list
        foreach $entry (<MAILLIST>) {

                chomp($entry); # get rid of that newline
                # print "$entry\n"; # test line
                # make sure the line isn't commented out
                if ($entry =~ /^#/) {

                        # print "We have a match: $entry\n"; # test line
                        # do nothing with these entries, they are commented
                        # out

                } # end the if commented

                else {

                        # this line isn't commented so send the notice
                        # to the user
                        open(MAILER, "| /bin/mail -s \"Gregs web server 
address is now $ipInfo[1]\" $entry ") || die "can't figure this out: #!\n";

                        print MAILER "\n\nThe address of Greg Brown's 
personal web server has changed.\n";
                        print MAILER "\nThe new IP Address is $ipInfo[1]\n";
                        print MAILER "\nGreg's Korean Adventure page can now 
be reached at the following address:\n";
                        print MAILER "\nhttp://$ipInfo[1]/korea/\n";
                        print MAILER "\n";
                        print MAILER ".\n";
                        print MAILER "\n";
                        close(MAILER);
 
                } # end the else not a commented line
 
        } #end the foreach loop
 
} # end the else loop
 
 
# now that we've send out all the e-mails telling everyone that there
# is a new IP addres let's write the new IP address to the file ip-eth1
 
open(IPINFONEW, ">/home/greg/scripts/ip-eth1");
 
print IPINFONEW "$ipInfo[1]\n";
close(IPINFONEW);
 
 
# and that's all she wrote, folks.

On Tuesday 01 October 2002 08:33 pm, you wrote:
> On Tue, 2002-10-01 at 19:04, Andrew Perrin wrote:
> > I was thinking about some scheme where when the IP changed, the
> > machine would scp a file containing its new IP address to my office
> > machine (which is fixed IP).
> >
> > Thanks for any comments!
> >
> > ----------------------------------------------------------------------
> > Andrew J Perrin - http://www.unc.edu/~aperrin
>
> That's exactly what I use for remote sites with dynamic IP addresses.
>
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