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11. Routing and other problems

11.1 My route to the remote keeps disappearing! It last for about 3 minutes and then the route just goes away. Help!

This is not a question for PPP.

Hint: DON'T RUN routed!

If you need to send RIP frames to the peer for its routing purposes then use the bcastd program. The bcastd program is on sunsite.unc.edu.

11.2 I would like to attach my other computers on my network to the Internet through my PPP connection. I have only the one IP address which is assigned to me from my service provider. (It may even have been dynamically assigned.) How may I do this?

You may not. At least, you can't do it in the manner that you would normally want to do it. The problem is that your provider would not know about the IP addresses of your local network and therefore wont route the frames to your local system.

There are other solutions, however.
  • You may telnet to your one computer running pppd and then use telnet or ftp to reach out to the rest of the Internet. This is not really much better then just using the computer directly, but it does work for simple things.
  • You may run a 2.x series kernel and use the \IP Masquerade\ option. For instructions on how to use this facility you should refer to the Net-2-HOWTO document.
  • You may run the socks program on your PPP system. This will perform the same facility as the IP Masquerade but it will take modified clients or a replacement run-time library. The advantage is that the socks program has been around for some years and many clients will understand the concept of a \proxy\ server which is needed to work with socks.

11.3 I can reach the remote server, but I can not get anywhere else.

Did you forget the \defaultroute\ parameter to pppd? This parameter adds a default route into your routing system so that frames to all other IP addresses will be sent to the PPP device.

The PPP software will not replace the default route if you have one already set when you run pppd. This is done to prevent people from destroying their default route to the ethernet routers by accident. A warning message is written to the system log if the defaultroute parameter is not performed for this reason.

11.4 I have a default route and I still can't get anywhere else! Now what?

The problem then is not with the local Linux system. It most likely is routing problem on the remote end.

The remote system is not configured for \IP forwarding\. It is an RFC requirement that this option NOT be enabled by default. You must enable the option. For Linux systems, you will need to build the kernel and specify that you want IP forwarding/gatewaying.

The remote computers need a route back to you just as you need a route to them. This may be accomplished by one of four methods. Each has advantages and limitations. You need to do one and only one of these.
  • Use a host route. At each host on the remote system, add a host route to your Linux IP address with the gateway being the terminal server that you use for your local access. This will work if you have a small number of host systems and a simple network without bridges, routers, gateways, etc.
  • Use a network route. Subdivide the remote IP addresses so that your local Linux IP address and the remote terminal server address and the remote terminal server\s ethernet address is on the same IP network. This will work if you have the IP addresses to spare. It will work very well if you have a Class-B IP network and can afford to put the all of the remote addresses on the same IP network. Then add a network route on each of the gateways and routers so that any address of the remote network is sent to the terminal server. Most configurations have many hosts but few routers. (At sii.com, we have over 300 active host systems with only 3 routers.)
  • Use gated on all of the gateways and on the terminal server. This will cause the terminal server to broadcast to the gateways that it can accept the frames for your IP address. Since the hosts will have a default route to one of the gateways, the gateways will generate the ICMP re-direct frame and the specific host will automatically add its host route.
  • Use proxy ARP on the terminal server. This will only work if your remote IP address is in the same IP domain as one of the domains for the network cards.

There is no clear solution. You must choose one of these.

If your remote router requires to receive RIP frames in order to update the route to your system then you should use the bcastd program on sunsite.unc.edu. This will generate the RIP frames without actually running gated.

11.5 I can not ping my local IP address

You are not able to do this because you wont normally have a route to the address. This is the normal operating environment.

If you wish to ping your own system then use the loopback address of

You may be able to ping the remote address. However, some terminal servers may not allow this as the address may be \phony\ to them. It depends upon their environment.

In general, don't try to ping either address. Choose a third address which is well known to be available on the remote network such as one of your name server IP address.

While the PPP software will not perform this task, you may add the route table entry yourself once the link has been established. The syntax for the route statement is:

route add -host lo

where the local IP address is represented as in this example. This will tell the network software to route all frames destined to your local IP address to the loopback adapter. Once you add the appropriate route to the local IP address then you may use this address as the target to IP frames.

You will be responsible for deleting the route when the link goes down.

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