Routing

When one network is connected to another, a device called a router connects both networks and passes data between them.

• In a simple ring network a packet may be routed around the ring until it gets ``caught'' or gets back to the sender.
• The Internet is not that simple -- multiple topologies.
• A router can be connected to more than one network.
• A router is, usually, a specialised computer with hardware and software specifically designed for routing network traffic. The problem is that hard.
• The route selected depends on traffic loads, what backbones are working etc.. Not all packets may be routed over the same route.

Some Routing Methods

Many different methods have been tried and many different strategies are in use today.

• Routing Tables -- specific maps (a list of routes) on how to get somewhere. Try one route from list until you succeed
• Centralised point -- send all traffic through a centralised node in a network.
• Nearest Neighbour (Centralised adaptive routing) -- a central node within each network knows only about its direct connections to the outside world. Send to nearest connection.

traceroute to www1.netscape.com (198.95.251.30), 30 hops max, 40 byte packets
1 cr1.cf.ac.uk (131.251.1.42) 2.382 ms 1.868 ms 1.952 ms
2 smds-gw.ulcc.ja.net (193.63.203.33) 8.456 ms 7.820 ms 8.711 ms
3 193.63.94.8 (193.63.94.8) 12.064 ms 9.730 ms 15.122 ms
4 icm-dc-1-S3/2-1984k.icp.net (192.157.65.113) 172.080 ms 168.902 ms 175.264 ms
5 icm-mae-e-H1/0-T3.icp.net (198.67.131.9) 162.964 ms *
6 192.41.177.180 (192.41.177.180) 167.341 ms * 156.772 ms
7 borderx2-hssi2-0.Washington.mci.net (204.70.74.117) 166.732 ms
8 core-fddi-1.Washington.mci.net (204.70.3.1) 246.142 ms 320.413 ms 301.374 ms
9 core1-hssi-4.LosAngeles.mci.net (204.70.1.177) 234.920 ms
10 core-hssi-2.SanFrancisco.mci.net (204.70.1.153) 495.669 ms *
11 border2-fddi0-0.SanFrancisco.mci.net (204.70.3.162) 383.403 ms
12 netscape.SanFrancisco.mci.net (204.70.33.10) 250.367 ms * *
13 www1.netscape.com (198.95.251.30) 243.961 ms

Trace Your Own Route on the WWW

You can trace your own route to the following Web site --- www.beach.net Note that on different runs of this at different times the routes will vary