UNIX System Administration Handbook - Evi Nemeth [231]
What’s great about all of these new developments is that regardless of the medium or its speed, TCP/IP is compatible with it.
15.9 NETWORK TESTING AND DEBUGGING
One major advantage of the large scale migration to Ethernet (and other UTP-based technologies) is the ease of network debugging. Since these networks can be analyzed link by link, hardware problems can often be isolated in seconds rather than days.
The key to debugging a network is to break it down into its component parts and test each piece until you’ve isolated the offending device or cable. The “idiot lights” on switches and hubs (such as “link status” and “packet traffic”) often provide immediate clues to the source of the problem. Top-notch documentation of your wiring scheme is essential for making these indicator lights work in your favor.
As with most tasks, having the right tools for the job is a big part of being able to get the job done right and without delay. The market offers two major types of network debugging tools (although they are quickly growing together).
The first is the hand-held cable analyzer. This device can measure the electrical characteristics of a given cable, including its length (with a groovy technology called “time domain reflectrometry”). Usually, these analyzers can also point out simple faults such as a broken or miswired cable. Our favorite product for LAN cable analysis is the Fluke LanMeter. It’s an all-in-one analyzer that can even perform IP pings across the network. High-end versions have their own web server that can show you historical statistics. For WAN (telco) circuits, the T-Berd line analyzer is the cat’s meow. The T-Berd and its high-end LAN-testing companion, the FireBERD, are made by TTC (www.ttc.com). Be forewarned: all these products cost as much as a small house in most cities.
The second type of debugging tool is the network sniffer. This device disassembles network packets to look for protocol errors, misconfigurations, and general snafus. It usually requires a substantial amount of training and patience to use such a device effectively, and these days analysis at the network-packet level is rarely necessary. If you must do it, the Cadillac of network sniffers is made by Sniffer Technologies (www.sniffer.com).
15.10 BUILDING WIRING
Whether you’re running gigabit Ethernet or just serial cables, we recommend that you use the highest possible quality of wire. It will increase the chances that you can still use the same wire ten years down the road. It’s cheapest to wire an entire building at once rather than wiring it one connection at a time.
UTP cabling options
Category 5E wire is relatively new and offers the best price vs. performance tradeoff in today’s market. Its normal format is four pairs per sheath, which is just right for a variety of data connections from RS-232 to gigabit Ethernet.
Category 5E specifications require that the twist be maintained to within half an inch of the connection to the punchdown block. This implies that any wire with more than four pairs per sheath will have to be taped or secured to maintain the twist, since it feeds more than one connection.
You must use Category 5E termination parts in addition to Category 5E wire. We’ve had the best luck using parts manufactured by The Siemon Company of Watertown, Connecticut (www.siemon.com).
Connections to offices
One connection per office is clearly not enough. But should you use two or four? We recommend four, for several reasons:
• They