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Ethernet is a method for communication also called CSMA/CD (carrier sense, media access / collision detect). It was developed at DEC first. It was cheaper than token ring for a Local Area Network (LAN) so it became the industrial standard. Ethernet has historically been used on copper cabling up to Gigabit speeds, but fibre-optic cabling is becoming very popular especially at Gigabit speeds. When ethernet is in a half-duplex setting (possibly connected to a hub) collisions can occur when two or more NICS broadcast at the same time. When a collission is detected a NIC will back off a random amount of time and try again, because the other cards also back off a random amount of time the odds are low that they will collide again. Today hubs are not used anymore but switches which eliminate the need to put cards in half duplex mode. If you only have one network card,

# /sbin/ifconfig -a | grep media
media: Ethernet autoselect (100baseTX <full-duplex>)

should show you what your network card is currently running at. If you have multiple cards, or are not getting the anticipated response, just try

# /sbin/ifconfig -a

On BSD, once you've determined your network device you can see what options it has in section 4 of the Manual. In this case I'm using sis0:

man 4 sis

Thinnet & Thicknet


Called Thin-net or Cheapernet. Today this is not used anymore.


Uses coaxial cable for a range of 500 meters without repeaters. Today this is not used anymore.

Twisted Pair & Fibre optics

10baseT Ethernet

Has a bandwidth of 10 Mbps (Mega bit per second). It can work in full duplex and half duplex mode. The maximum length of one copper ethernet cable between 2 NIC's is 100 meters, 200 meters if a ethernet repeater is used, which boosts the signal.

100baseT Fast Ethernet

Has a bandwidth of 100 Mbps. It can work in full duplex and half duplex mode. The maximum length between 2 NICS is the same as 10 Mbps ethernet.

1000baseT Gigabit Ethernet

Has a bandwidth of 1000 Mbps. It can work in full duplex and half duplex mode.

10 Gigabit Ethernet

Has a bandwidth of 10 Gbps (Giga bit per second). It probably works in full duplex mode.

Twisted Pair Copper Cabling

Ethernet copper cabling also called Twisted Pair cabling is composed of 4 pairs of copper wire which are twisted between the pairs and also twisted around in their plastic protective coating. The twist is to ensure shielding which is questionable. The ends of ethernet cabling are connectors called RJ-45 bits. The individual wires are colour coded and are visible in the RJ-45 connector from the top. The most common sequence is 1. green-white 2. green 3. orange-white 4. blue 5. blue-white 6. orange 7. brown-white 8. brown. This is the setup on both ends for what is called a straight-thru cable. The only wires actually used are positions 1, 2, 3 and 6. When you want to connect 2 ethernet cards directly without use of a hub or switch you require a cable that is crossed-over or a cross-over cable. This is called so because positions 1 and 3 and 2 and 6 are crossed, so the end of the crossed end looks like this 1. orange-white 2. orange 3. green-white 4. blue 5. blue-white 6. green 7. brown-white 8. brown. The most common type of cabling for ethernet is category 5 cabling although there is category 5e now for gigabit. To attach the RJ-45 bits to the cabling a special tool called a RJ-45 crimper is used. Cheap version s are about $30 (CA) at cabling surplus stores.

File:Rj45-st.jpg File:Rj45-co.jpg

Wireless LAN

WLAN also called Wifi was first developed at Lucent with their Wavelan product. It is a standard based around IEEE 802.11b and g. At first Wifi could speak only 11 Mbps maximum which was then upgraded to 54 Mbps with the 802.11g standard. Wifi came with built-in encryption at first called WEP but the implementation of this cryptography was breakable. It should be noted that all Wifi should be encrypted with ipsec to ensure additional security.



PPP over Ethernet is a hack of protocol spoken with most DSL home end-user connections. It is covered in RFC 2516 and involves packet encapsulation, a packet within a packet. As a result a PPPoE user will often have to dumb down their MTU and/or MRU settings. Although the default is usually 1500, this author has the following in his ppp.conf:

set mru 1492
set mtu 1452

as the best setting for his PPPoE sDSL connection.