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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
<TITLE> Setting up dynamic IP web server via PPP connection </TITLE>
<META NAME="GENERATOR" CONTENT="Mozilla/3.0Gold (X11; I; Linux 2.0.0 i486) [Netscape]">
</HEAD>
<BODY>
<H4>"Linux Gazette...<I>making Linux just a little more fun!</I>
"</H4>
<P> <HR> <P>
<!--===================================================================-->
<center><H1>Setting up dynamic IP web server via PPP connection</H1></center>
<center><H4>By Henry H. Lu, <A HREF="mailto:honglu@rt66.com">honglu@rt66.com</A>,
<A HREF="http://www.tc.umn.edu/nlhome/m508/luxxx012/">http://www.tc.umn.edu/nlhome/m508/luxxx012/</A>
</H4> </center>
<center><H5>Copyright (c) 1996</H5></center>
<center> <H5>Published in Issue 10 of the Linux Gazette</H5></center>
<P>Have you been thinking of seting up a reachable web server at your home
PC in addition to your permenent page at ISP? There are obvious reasons
to do this: You can show off your home linux box to the world; you do not
need to use other messy method (email) to know your current IP in order
to login remotely; finally, it is fun! </P>
<P>First, You need to have ppp connection and httpd working and a PERMANENT
web page before trying the following dynamic IP solution. </P>
<H3>Description of files: </H3>
<P><B>web_up: </B>shell script I run to update webpage at permenet site
with new IP whenever connection is up. </P>
<P><B>web_down:</B> shell script I run before shutting down the link, to
inform others of the shutdown </P>
<P><B>update_uppage:</B> perl scripts to creat up.html page with updated
IP address on the fly, called by web_up. </P>
<P><B>up.html_source:</B> fixed part of up.html </P>
<P><B>down.html:</B> web page used when link is down. </P>
<P><B>/etc/add, /etc/last_add:</B> files where I put IP address. </P>
<P><B>ip-down, ip-up:</B> files executed when ppp link is disconnected
or connected. they are used to update the /etc/add files here. </P>
<H3>Now lets look at scripts web_up: </H3>
<PRE>------------------------------------------------------------------
#!/bin/sh
#check new IP
new_ip()
{
if [ -f /etc/add ]; then
if [ -f /etc/last_add ]; then
if /usr/bin/diff /etc/add /etc/last_add >/dev/null ; then
exit 1
else
return 0
fi
else
return 0
fi
else
exit 1
fi
}
#check whether maroon is connected
try_connect()
{
if ping -c4 -l3 128.101.118.21 2>&1 | grep "0 packets" > /dev/null
then
return 1
else
return 0
fi
}
if try_connect
then
touch /var/run/maroon_connected
else
rm -f /var/run/maroon_connected
fi
# ftp to update page
if [ -f /var/run/maroon_connected ] && new_ip
then
# update_uppage is perl scripts, exit status is opposite of shell
if ( ! /home/honglu/public_html/update_uppage )
then
cd /home/honglu/public_html
if echo "put up.html /nlhome/m508/luxxx012/dynamic.html" \
| /usr/bin/ftp maroon
then
rm -f /etc/last_add
cp /etc/add /etc/last_add
exit 0
else
exit 1
fi
fi
else
exit 1
fi
-----------------------------------------------------------------
</PRE>
<P>Now let's look at web_up in detail. </P>
<P>Function <B>new_ip()</B> is used to check whether we have new IP and
whether the new IP is different from the last one. /etc/ppp/ip-up and /etc/ppp/ip-down
update IP adress in files /etc/add and /etc/last_add so that we can compare
files "add" with "last_add" to tell whether we need
to update page. </P>
<P>Function <B>try_connect()</B> is used to test whether the perment web
site is reachable. </P>
<P>Next is fun part, I used automatic feature of <B>ftp</B> to update webpage.
In order to make it work, you have to set file ~/.netrc correctly, type
"man ftp" for more information. </P>
<P><B>update_uppage</B> is straitforward perl scripts to parse and creat
up.html by using new IP from /etc/add file. </P>
<P>Final part is to update /etc/add /etc/last_add to reflect correct status
IP address. </P>
<P>You can put "web_up" in your crontab entry ( or ip-up, or
keapalive.sh) to let it execute automatically whenever your PC is connected.</P>
<H3>Web_down is a similar page, main difference is in ftp part: </H3>
<PRE>-----------------------------------------------------
......
......
# ftp to send down.html page
if [ -f /var/run/maroon_connected ]
then
cd /home/honglu/public_html
if echo "put down.html /nlhome/m508/luxxx012/dynamic.html" \
| /usr/bin/ftp maroon
then
rm -f /etc/last_add
else
exit 1
fi
else
exit 1
fi
----------------------------------------------------
</PRE>
<P>Instead of ftp up.html as web_up did, web_down put down.html to permenent
web site to inform the delink of page. </P>
<P>web_down should be run before you shut down the machine. I created a
scripts called "shut" to shutdown machine: </P>
<PRE>-----------------------------------------
#!/bin/sh
if web_down
then
shutdown -h now
else
echo "can not web_down"
exit 1
fi
-----------------------------------------
</PRE>
<P>For more detail check out my home page for source code: </P>
<P><A HREF="http://www.tc.umn.edu/nlhome/g625/luxxx024/">http://www.tc.umn.edu/nlhome/g625/luxxx024/</A></P>
<P>Henry H Lu
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