Unix Guide Page 19 - Hardware and Cabling

19. Hardware and Cabling

Cabling Types
Data Protocol	Wire Specs	Characteristics	Max Length	Shielded?
10T (10 Base T)	UTP/Twisted Pair/Cat 5 Cable	Has 6 connectors. Pins 2,3, & 7 are usually used. Resembles common phone cable	50 Meters (62.5 ft)	No
10₂ (10 Base 2)	Thinnet or Coax	1 connector. Outside part of cable is part of the circuit (two cables are required for a circuit.) Resembles cable TV cable.	185 Meters (225 ft) (max is 1200 ft with repeaters)	No
10₅ (10 Base 5)	Thick Net	7 connectors.	500 Meters (625 ft)	Yes
For a cable to be considered shielded, it needs a metal braid, and a separate ground.

Terms

Properties of cable

Hardware

Hubs – amplify and forwards info, and can only do one send at a time
Switches – (similar to a hub) has a buffer that holds packets when one is already sending, and it sends info to only computer it was meant for runs at speed times number of ports runs on Ethernet address.
Repeater – basically a hub with two ports, amplifies a signal to increase its reliability and possible distance.
Router – transfers datagrams between networks (the difference between a router and a switch is that a router transfers between networks, which a switch works in a network, sending datagrams to specific areas.)
Bridge – basically a switch with 2 ports that translates between routing protocols.

Device levels

Hardware level devices are devices that ignore the data, they just pass the info along (Passive.)
1. Interfaces
2. Hubs (don’t communicate with other hubs, rather they look for routers)
Ethernet level devices are ones that listen to the Ethernet address and send or don’t. These are considered passive.
1. Switches
2. Bridges
IP layer devices use the IP address and decide whether to forward or not, based on the IP. These devices are considered active.
1. Routers
2. Firewalls
Out of these, only devices under the IP layer have addresses that packets are sent to, and they manipulate the data. The others just send the information along.

Commands

Command to work with each interface – ifconfig (Sample hardware interfaces, le0 [lance Ethernet], ie0 [intelligent Ethernet], hme0, bme0 qe0 [quad Ethernet]) 0 is the first card you have (Sample software interfaces, lo0 [loopback interface, kernel])
ifconfig –a – shows all plumbed interfaces (plumbed means kernel has recognized it)
ifconfig [interface name] plumb – makes the kernel recognize interface (able to be configured by the kernel)
ifconfig [interface name] unplumb – lose the config of the interface and remove it from the kernel
ifconfig [interface name] ether [Ethernet address] (ie: ifconfig hme1 ether 8:0:20:4a:5b:6c) chooses the Ethernet address (not recommended, useful for licensing issues and when the programmable read only memory (prom) fails)
ifconfig [interface name] up – tells the kernel to use this interface. ifconfig [interface name] down – tells the kernel not to use this interface
at +10 reboot – this command will reboot the computer after 10 minutes, so that if you make a mistake and lock yourself out, it will reboot. Configuring devices can lock you out.

Go to Chapter 18 Go to Index Go to Chapter 20