Remote Logins

You are on the move and need

to access some files from your office computer. Wouldn’t it be nice to dial up your

office server and download the files using FTP? You can do just that with a remote dial-in

server running on your organization’s network. In this article, we’ll explain

how to configure a remote dial-in server in Red Hat Linux using the PPP protocol.

The first step is to install the modem. Plug in the modem’s

serial cable into a spare serial port on your computer. A phone-line should also be

connected to your modem. Start Linux and log in as root. You should remain logged in as

root throughout the setup process. You should also start the X Windowing system.

Fire up glint, the X interface to the Red Hat Package Manager, and

check whether mgetty and PPP packages are installed. mgetty can be found in the

Networking/Utilities folder and PPP in the Networking/Daemons folder.

If these packages aren’t installed on your system, mount the PC

Quest CD in /mnt/cdrom. Once the CD is mounted, switch over to glint and click on the

Available button. Glint should show you a list of available packages arranged in a series

of folders. Double click on the Networking folder and then on the Daemons folder. Search

for the PPP package, select it and click on the Install button. Glint should now install

the PPP package.

Similarly, move to the Networking/Utilities folder, search for the

mgetty package and install it.

Okay, now that both PPP and mgetty have been installed, the next

step is to configure the two packages. Let’s start with mgetty first. Mgetty is a

replacement for the standard Unix getty, capable of handling serial connections. The getty

process is responsible for the login prompt and getting the login name from the user. Open

up the /etc/inittab file in your favorite text editor and add

V1:2345:respawn:/sbin/mgetty -s 115200 ttyS0

at the end. When Linux starts, the init process goes through this

file, looking for processes to execute. The option 2345 tells init to run the mgetty

process in the multi-user run levels 2, 3, 4, and 5. The respawn option allows mgetty to

restart every time it terminates.

Let’s examine the parameters given to mgetty itself. The

parameter "-s 115200" directs mgetty to use the serial port at the highest

possible speed, 11,5200 bps. Remember that this is the speed at which the computer

communicates with the modem. The modem usually talks to other modems at a lower speed. The

last parameter, ttyS0 should be used if your modem is connected to the serial port, COM1.

If your modem is on COM2, type ttyS1 instead.

Remember that mgetty will lock the modem for its own use. If you

wish to use the server for dialing out, you’ll have to terminate the mgetty process

either manually or through some shell scripts.

Since we plan to use Windows Dialup Networking to connect, it makes

sense to enable PAP authentication, that way users don’t have to mess with stuff like

dial-in scripts.

Edit the file /etc/mgetty+sendfax/login.config, and make sure that

the line with "/AutoPPP/" is uncommented, remove the # mark in front of it, and

edit it so that it looks like this:

/AutoPPP/ - - /etc/ppp/ppplogin

Save the file. Notice that this points to a file called /etc/ppp/ppplogin, we need

to create this one. It’s a small file that has the following contents:

#!/bin/sh



mesg n


tty -echo


/usr/sbin/pppd silent auth -chap +pap login

Save the file and make it executable:

chmod +x /etc/ppp/ppplogin

Now create or update the /etc/ppp/options file:

-detach



modem


lock


crtscts


asyncmap 0


netmask 255.255.255.0


proxyarp


ms-dns

In the above replace with the IP address of your

LAN’s DNS server. In our case, the machine 192.168.1.15 acts as our DNS, so we used:

ms-dns 192.168.1.15

Create another file /etc/ppp/options.ttyS0 and add the following to

it:

For example, we used ws120.cmil.com:192.168.1.200

The hostname can be had by running the hostname command. You could

also look into the /etc/HOSTNAME file. The second address is allocated to the remote

system. Any unused IP address on your network should do.

Also remember to set PPPD as SUID root as it configures a network

interface and manipulates kernel routing tables. All this requires special privileges. To

do this, run the command:

# chmod +s /usr/sbin/pppd

Finally, let’s update the PAP authentication database. This is

simple, we are going to validate users against the standard /etc/passwd, so all you need

to do is edit the file /etc/ppp/pap-secrets, and add one line for every IP address you are

going to allocate to a dial-in connection. In our setup, /etc/ppp/pap-secrets looks like

this:

# Secrets for authentication using

PAP



# client server secret IP addresses


* * "" 192.168.1.200

You might add more lines that are identical to the last one shown

above, one for every IP address you’ll be using. That’s it. Now run the command "init q" which will

re-read the file /etc/inittab and start the required processes. Now, dial-in PPP should be

up and running, you can check this on your modem, the DTR light will have come on.

To connect via PPP, dial in from any other system using dial up

networking.

To connect from a Win 9x system, go to Dialup Networking in My

Computer, select "Make a New Connection", enter some name (such as "Linux

dialup"), make sure the correct modem is selected (and optionally configure it), and

press Next. Do not select "bring up terminal after dialing" in the modem

configuration, it’s not required. Nor should you assign a dialup-script.

Enter the telephone number that is attached to your modem, press

Next, and then finish the setup. Now right click the newly created connection, go to

"Server Types" and disable "Log on to Network", NetBEUI and IPX/SPX

Compatible, leaving only "TCP/IP" and "Enable Software Compression"

ticked. Click on OK.

That’s it. Now to connect from the Win 9x machine, double click

the new connection, enter your user ID and password (and optionally tell the system to

remember your password), click on connect, and your Windows machine will dial into the

Linux box, connect, establish PPP, and voila! You are on! Check it out by pointing your

browser to your Linux box, you should see the Web pages stored there. Tell your mail

client to send and receive mail via the Linux box, and that too works.

While reading this, you might feel that the setup is complex.

Don’t let this detailed article scare you away. We thought the same but the whole

process took us a little less than five minutes, and was far easier than configuring a Win

NT RAS server.