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Mandrake Linux 8.0 and later offer an easy way to configure connection
sharing via the Mandrake Control Center. Mandrake Linux user Kevin McCormick
however wasn't content with this basic setup. In this article he describes how
to connect a small home network via a Mandrake Linux machine using a dialer
and a DNS cache.
The network consists of three machines, two of them running Mandrake Linux
and one MS Windows 95. They are connected via a hub, the uplink is established
via an ISDN Terminal Adapter (TA). The machine to which this adapter is
connected to is referred to as the server. It has the IP 192.168.1.1. This IP
is configured as the DNS server address on the clients. Make sure that
FORWARD_IPV4 is set to true in
'/etc/sysconfig/network' on the machine which act as the Internet gateway.
The article assumes that the local network is up and running. If it isn't,
refer to the article on Establishing A Local
TCP/IP Network. It also assumes that PPP dial-up is working on the machine
which is connected to the Internet.
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The "feature" of this configuration is the dialer and DNS cache. The dialer
program is called dwun ('Dialer
Without Useful Name'), and the DNS cache is called pdnsd (Proxy DNS
Daemon). These programs allow any computer on the network to dial the ISP for
web surfing or e-mail, as long as the server is running.
Both projects offer source archives or precompiled RPM archives which
should work fine on every Mandrake Linux 8.x system.
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For 'dwun', the preliminary details that must be resolved are the serial
port and modem device file. In my case, the ISDN TA is attached to the first
serial port '/dev/ttyS1', but that device will often be identified by a
symlink, '/dev/modem'. Once that is verified, the proper modem initialization
commands must be determined. This can be discovered by reading the modem user
manual, and perhaps with minicom, a terminal communications program that comes
with Mandrake and many other distributions.
For my setup, 'dwun' uses 'pppd' (Point to Point Protocol daemon) and
'chat', which establishes the connection between the local pppd and that of
your provider.
The directions are found in the README file in the 'examples/chatscripts'
directory.
The basic sequence of events in activating dwun is 1) read the '/etc/dwunrc'
file at startup, 2) when requested, execute 'pppd' using a 'chat' script, and
3) when no computer in the network is asking for the Internet connection,
disconnect and shut down 'pppd'.
The options for pppd are typically found in a file called
'/etc/ppp/options'. For 'dwun', however, you should back up that file and
delete all lines from the original file.
According to man pppd, if 'pppd' is called with the argument
call name, then 'pppd' will read the options from
'/etc/ppp/peers/name'. This is the method used by 'dwun' in my
setup. Thus, the '/etc/dwunrc' file contains the line:
commandon /usr/sbin/pppd call dwun
and the file '/etc/ppp/peers/dwun' contains all the options for the 'pppd'
daemon. The '/etc/ppp/peers/dwun' file in turn contains the line:
connect "/etc/dwun.chatscript /etc/ppp/phonelist"
which directs 'pppd' to initialize by using the chat script found in
'/etc/dwun.chatscript', which takes the argument '/etc/ppp/phonelist'.
Once the initialization commands for the modem are known, the
'/etc/dwun.chatscript' file (the former 'chat.pap-chap' template from
'examples/chatscripts') must be edited to include these in the expect/send
pairs, as well as the proper CONNECT message to expect. An
excerpt from my 'dwun.chatscript', which is contained in the
dial() function shows what works for me:
"" "AT &F S60=64" \
OK ATD\\T \
"CONNECT 115200" \d\c
Note the ATD\\T. The \\T is actually a placeholder for the ISP
telephone number, placed in the '/etc/ppp/phonelist' file (so the phonelist
file should not have blank or comment lines). This does allow one to have
several ISP telephone numbers for 'dwun' to try in sequence until one actually
works. The CONNECT 115200 argument is probably a feature of my
3ComImpactIQ ISDN TA.
Then, following the directions provided by the 'dwun' author, the
'/etc/ppp/ip-up.local' and '/etc/ppp/ip-down.local' files are edited. All of
the suggested changes have worked fine for me without touching the ip-up or
ip-down scripts.
This completes the server discussion regarding dwun.
The client programs for dwun are really quite simple. Install 'gcdial' either
from source or RPM. WinDWUN is for MS Windows 9x
and 2000 machines and comes as an .exe which unpacks and installs
itself.
Both have a very simple setup and work reliably. To use the clients, simply
click on the client icon, click the connect button, and start your
webbrowser.
For MS Windows, Netscape should be set to "direct connection to internet" and
not to a proxy.
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Now on to the setup of 'pdnsd'. There is one relevant point regarding the
'/etc/ppp/peers/dwun' file. Do not include the option 'usepeerdns' if you
intend to use 'pdnsd' or your own caching nameserver.
The 'pdnsd' program has the benefits of providing name resolution without
the overhead of BIND DNS. Also, it uses a cache file, so the name/address
lookup results are not totally lost every time the server is restarted. My
experience has shown an improvement is apparent server performance.
After installation, the '/etc' directory will contain a file called
'pdnsd.conf.sample'. Copy that file and rename it to 'pdnsd.conf'.
'pdnsd.conf' consists of two section which are of interest, 'global' and
'server'. Each option=value line ends with a semi-colon. In the 'global'
section, I set perm-cache=2048, paranoid=on,
daemon=on, and server_ip="192.168.1.1".
The 'ip' entry in the 'server' section should point to your service
provider's DNS address as listed in '/etc/resolv.conf'. If provider offers
more than one DNS address, duplicate the 'server' section and enter the second
DNS address in the 'ip' field of the duplicated 'server' section.
Back up '/etc/resolv.conf' next. Replace all content in the original file
with the line
nameserver 127.0.0.1
Restart the network as 'root' with
service network restart
Now start 'pdnsd' as 'root' with
service pdnsd start
Notice that 'pdnsd' opens port 53 on the server.
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Both dwun and pdnsd should show up in DrakConf | System | Services
Well, that does it for the How-To. I have no idea how secure these programs
are, but I have not detected any problems. I have found this setup to be
reliable and trouble free, and it seems that web surfing is faster. Everyone
can learn to click on the dwun client icon and then the browser icon, so I do
not have to assist with web-surfing very much. I hope this commentary has been
helpful.
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