A Few Caveats

If you have played with LILO (the LInux LOader), /vmlinuz may very well not be your system kernel.Check /etc/lilo.conf if you’re unsure.

Make sure you use networking tools that match your kernel version -- all sorts of strange things can happen with a mismatch! Specifically, watch out for arp, route, ifconfig, and gated. A good rule of thumb is to stick to the versions that come on the CD-ROM distribution. If you’re getting your files from the Internet, pay close attention to READMEs.

Stick to the defaults when configuring by hitting ENTER at the prompts. Be sure you don’t configure a device that you don’t have -- if you do, you risk lockups and erratic system behavior.
In our case, we also had to scour the earth for a Token Ring driver for Linux, and compile it into our kernel, but that’s another long story. If you are looking for Token Ring support, and are willing to live without busmastering and TI chipset support, check out Peter De Schrijver’s Wonderful Token Ring driver:

ftp://linux3.cc.kuleuven .ac.be/pub/Linux

or

ftp://ftp.cs.kuleuven.ac.be/pub/unix/linux

See Terry Dawson’s comprehensive NET2-HOWTO for current information on available networking technology support. Look in:

ftp://sunsite.unc.edu/pub/Linux/docs/linux-doc-project/network-guide

Token Ring may well be included in many distributions by the time you read this. I will mention, however, that we had problems using kernels earlier than 1.2.

Once the kernel was recompiled and ready to forward packets according to its routing table, we needed to give it routing "smarts," so we started up routed, the ancient routing daemon. This was a mistake; routed is obsolete and flakey, and should not be used here. Instead, use gated. It will speak every routing protocol you’re ever likely to need, and it is easy to configure for RIP (see Figure 2). If you need to use something other than RIP, say, OSPF, you can rest easy knowing that the gated distribution has quite a few sample configuration files for you to copy.

Any router needs more than one interface to be useful, and our Linux router was no exception. We chose to use PPP (Point-to-Point Protocol) in conjunction with ISDN terminal adaptors, because ISDN service is extremely inexpensive here. (ISDN was not supported with most Linux distributions at the time, but itmay be by the time you read this.)

Also, pppd, the point-to-point daemon, supports "proxy arp," which lets you avoid wasting a network on the point-to-point link. Basically, proxy arp makes your remote machine’s point-to-point interface appear as if it is on your local network, in our case, the 167.195.160 network (see Figure 1).

The pppd support for a Token-Ring frame type was not complete at the time of this writing. The version of pppd that we used (2.1.2) would proxy-arp, but with a frame type of Ethernet, not Token Ring. The files /etc/ppp/ip-down and /etc/ppp/ip-up (Figure 3) were necessary in order to kludge the proxy arp on the local end. You don’t have to do this if you’re using Ethernet, or if this has been fixed in your version of the pppd.

We chose terminal adaptors that would turn a synchronous 64Kbps channel into an asynchronous 57.6Kbps channel, so that we could use a standard 16550 UART serial port, /dev/ttyS0 on both machines. Note that you must use a 16550 or other buffered or intelligent serial port to run at this speed (or 128K synch transformed into 115K asynch). If you do not, you will experience data overruns and thus network errors.

Also note that when using Linux, if you want to use serial speeds above 38,400Bps, you must use the setserial program to make the 38,400 transform into either 57,600Bps (spd_hi) or 115,000Bps (spd_vhi) (see Figure 4 for details).