asked on

Dynamic address broadcasting

Hello,

My Linux box gets its address via DHCP, making it sometimes hard for me to find from outside.

I would like it to write its address on a web page whenever it boots up or gets a new address. Does anyone have a script that does something like this?
Note: I can only use FTP to access the webserver where I want to post the info (ISP's rules).

Thanks,
CubeDweller

jlevie

It would be easy enough to construct a script that could be run from cron or at boot up. I'd think I'd do it from cron, say every half hour, as I don't know how you'd determine if the address had been re-negotiated.

The script would:

1) Get the ip out of an ifconfig.

2) Compare the current IP against a saved copy and if they are different make the new ip become the saved IP and ftp the saved data to the web page using ncftput.

I'd do it with a perl script as it seems to me it'd be easier. I don't have time right now to whip one up, but I'll give it a shot later if someone else doesn't come up with a script in the meantime.

There are places on the Internet that offer this kind of service. Typical costs seem to be in the $20-40 a year and you can have a DNS record associated with the IP. I thought I had a bookmark, but if you do a search on "dynamic dns services" you ought to turn up soemthing.

Alien Life-Form

Greetings.

If you can do cgi-bin on a web server,
you could try something in the line of the following script (untested and I am omitting error checks, etc.):

# your machine ethernet address
ETH='08:00:xx:xx'
#
BCAST='192.168.0.255'
#
ping -q -b -c 5 1> /dev/null 2>&1

SELF=`arp -a | grep $ETH | awk '{print $1}'`

echo 'Content-type: text/plain'
echo ''
echo "You will find yourself as $SELF"

exit 0

The only snag is that the web server this goes on has to be on the same physical segment of your machine (so ping/arp will work, as these days routers tend to drop IP-directed broadcasts. Also, this technique has a (quite low) potential for getting on a netadmin nerves if it gets hit too often.

Actually, I just found out that only root can 'ping -b'. Whoops. Now that's a pity, cause I sorta liked this... So I will post the comment anyway. (I do not think the sysadmin would chmod +s this script...)

Cheers
alf

cubedweller

ASKER

Maybe it would help if I explain exactly what I am trying to do:

I have a couple hundred megs of web content, but an ISP that only gives me 5 megs of space (RoadRunner). I figure I can get around this limitation by hosting the vast majority of the site on my Linux box.

I want to make it a seamless user experience, so I hope to write my current IP address into the META http-equiv="refresh" tag on key pages. This would automatically redirect the user to the right server.

Thanks

ASKER CERTIFIED SOLUTION

jlevie

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cubedweller

ASKER

Alright, jlevie, you convinced me. I went with dyndns.

Thanks again,
CubeDweller

jlevie

Yeah, it just seems like a simpler solution. There are dynamic dns servers that'll service an actual domain name for you (that you'd get registered) rather than the pseudo domain like dyndns uses. I haven't located any free ones though. About $25 or so per year seems to be the norm.