The FreeBSD Diary

I thank the following people for their help in developing these scripts:

Harold Jarvie - for developing the original script.

Burke Gallagher - for converting the script to use sockets.

Jake Burkholder - for showing me how to send mail from within PERL.

I've also been given another script by Dragon Knight <dragonk@mato.com>.  It also works with yi.org.   Have a look at  dragon.yi.org.sh.  Please note that the script runs under bash and produces an error if run under sh.

DNS (Domain Name Service) is the method by which IP addresses and domain names are associated.  If your IP address changes, then you need to update your DNS records to reflect this change.  And perhaps people will find another website instead of yours.

Several organizations exist which supply dynamic DNS services.  Here are the ones I know about.  If you know of any more, please give us your comments.

URL	Site Title
http://www.yi.org/	Quick, Easy, Painless Dynamic DNS
http://detour.net/	Project Detour
http://tjns.tj/	TJ Network Services
http://www.dhis.org/	Dynamic Host Information System
http://www.dnswiz.com/	DNS Wizard Corporation
http://www.easydns.com/	Easy DNS (not sure they provide Dynamic DNS)
http://www.dyndns.org/	Dynamic DNS Network Services
http://www.tzo.com	The TZO Internet Naming Utility ($24.95)

I use yi.org, but I'm sure you'll be able to substitute the script from your DYNDNS provider.  Some of the above are free, some of them cost.  You get what you pay for.

Make sure the the code from your DYNDNS provider actually updates their DNS for you.   This is the most important step.  If you have trouble here, please contact your DYNDNS provider.

obtain_ip.pl	a perl script run every ten minutes from /etc/crontab
myip.txt	stores the last known IP address
fetch_results.html	holds the result of the last attempt to update our DNS
dns_fetch.sh	a shell script provided by yi.org but modified for my purposes.  runs when a change in IP address is detected. (html version)

I have an ADSL modem/router.  It is this router which actually receives the new IP address.  My FreeBSD box retains the same address all the time, but it is a private address and is not accessible via the Internet (i.g. it's a 192..168.*.* address).  The router has a www interface, so I can browse to it and see what the IP address is for it.   This is pretty simple.  I've provided a screen shot of this interface.  The IP address we need to find is in bold.  It is the FetchM10Address routine in obtain_ip.pl which parses this interface and extracts the current IP.

I run the perl script.  Here is the entry in /etc/crontab which I use to start my script every ten minutes:

*/10 * * * * dan /home/dan/obtain_ip.pl > /dev/null

One thing to note is that I am not using the default yi.org solution.  I had problems running lynx from a cron job.  So I modified the script to use fetch.

1. Every ten minutes, the cron job starts up /usr/home/dan/obtain_ip.pl.
2. This code queries the ADSL router for the current IP address.
3. The current IP address is compared against the last IP address which was stored in /usr/home/dan/myip.txt.
4. If the IP address has changed, the script from the DYNDNS provider (/usr/home/dan/dns_fetch.sh) is invoked.
5. The results of that dns update are stored in /user/home/dan/fetch_results.html.

# perl obtain_ip.pl 
DYNDNS
currentIP = 210.55.152.48,  lastIP = 
change detected
Updating to IP 210.55.152.48
count = 2

Result = '1'
update succeeded

Here are the log entries it generated:

Jul 18 17:29:50 ns DYDNS[23394]: start
Jul 18 17:29:55 ns DYDNS[23401]: The IP Address has changed to 
                                                         210.55.152.48
Jul 18 17:29:56 ns DYDNS[23405]: stopped

And here's the email message you should get.  Note that the message contains HTML because that's what the yi.org script fetches.  It is a www interface.

$ mail
Mail version 8.1 6/6/93.  Type ? for help.
"/var/mail/dan": 1 message 1 new
>N  1 dan              Sun Jul 18 17:30  24/930   "Dynamic DNS change"
& 1
Message 1:
From dan Sun Jul 18 17:30:04 1999
Date: Sun, 18 Jul 1999 17:29:58 +1200 (NZST)
From: Dan <dan>
To: dan, root
Subject: Dynamic DNS change

The IP Address has changed to 210.55.152.48
<HTML>
<HEAD><TITLE>yi.org Domain Update Request</TITLE></HEAD>
<BODY>This update will only service IP changes. To reconfigure your
yi.org settings, please use the account editor available at
<A HREF="http://www.yi.org/">www.yi.org</A>.<BR>
<!-- MS3V STATUS:OK HOSTNAME:yourdomain ACT:1 IP:210.55.152.48 MX:na 
                                                                   -->
Your request has been processed successfully.
<UL><LI><B>Domain Name:</B> yourdomain</LI>
<LI><B>IP Address:</B> 210.55.152.48</LI></UL>
<EM>Report errors to <A HREF="mailto:yi@yi.org">yi@yi.org</A></EM><BR>
</BODY></HTML>

The next time you rung the perl script, you should see this:

# perl obtain_ip.pl 
DYNDNS
currentIP = 210.55.152.48,  lastIP = 210.55.152.48

Here are the log entries that will generate:

Jul 18 17:36:17 ns DYDNS[23425]: start
Jul 18 17:36:18 ns DYDNS[23426]: stopped

$ nslookup ftp.freebsd.org
Server:  localhost.yourdomain.org
Address:  127.0.0.1

Non-authoritative answer:
Name:    wcarchive.cdrom.com
Address:  209.155.82.18
Aliases:  ftp.freebsd.org

A domain alias is easy to set up.  It is most often done with a CNAME.  For example, here's what I use as the zone file for racingsystem.cx:

@       IN      SOA     rock.ghis.net. soa.dvl-software.com.  (
                                199907031       ; Serial
                                3600    ; Refresh
                                900     ; Retry
                                3600000 ; Expire
                                3600 )  ; Minimum

; name servers

                IN      NS      ns.ghis.net.
                IN      NS      ns.freebsddiary.cx.
                IN      MX      5       freebsddiary.yi.org.
;
; Define the rest of my subnet
;

www.freebsddiary.cx.            IN CNAME        freebsddiary.yi.org.
ww3.racingsystem.cx.            IN CNAME        freebsddiary.yi.org.

With this setup, people can get to my box at home using www.freebsddiary.cx.  This will have the same IP address as freebsddiary.yi.org.  To learn how different websites can share the same IP addresss, see Virtual Hosts.

Best wishes.  And I hope this helps.