- NIC: Network Interface Card.
- OSI: Open System Interconnection. This is
a standard/model for networking. The OSI model slices network
protocols into 7 layers, from physical (electrical voltages
and other physical properties) to application (logical/abstract).
- MAC Address: Media Access Control
Address. Each interface should have a unique MAC address to
uniquely identify itself. In reality, MAC addresses can be
cloned. That is, one NIC can assume the MAC address of another
NIC. MAC addresses are used mostly in OSI layer 2 protocols.
- TCP/IP: Transfer and Control Protocol/Internet
Protocol. TCP implies IP, but not the other way round. In order to
connect to the Internet, a computer must understand how to
speak the language: TCP/IP. IP specifies layer 3 in the OSI
model, while TCP builds on top of IP at layer 4 in the OSI model.
- LAN: Local Area Network. This is a bunch of computers
linked by a network that is relatively local (close to each
other).
- WAN: Wide Area Network. This is a bunch of computers
that are not close to each other, linked together by a network.
A WAN may link multiple LANs together.
- hub: A hub connects multiple network interfaces
together. A hub only works for certain types of LANs, such as
ethernet. Logically, a hub allows every network interface
listen to every other network interface connected to the hub.
- switch: A switch connects multiple network interfaces
together. Unlike a hub, however, a switch does not broadcast
messages to all interfaces. Instead, a switch understands
enough protocol (OSI layer 2, and a little bit of layer 3)
to direct traffic as needed. Consequently,
when a message is sent, only the intended network interface
receives it. All other network interfaces connected to the same
switch do not receive cross traffic not intended for them.
- router: A router connects multiple network interfaces
like a switch or a hub. However, a router understands
higher level protocols (OSI layers 3 and 4). As a result,
a router differs from a switch because it can connect
network interfaces with different IP address ``families''.
As the name implies, a router can also decide how to forward
a packet of information based on traffic pattern and static
routing information. Some routers are intelligent enough to
masquerade an entire LAN as a single IP address (via
NAT, network address translation).
- firewall: A firewall is a
programmable filter that operates at layers 2 to 7 in the OSI
model. In short, a firewall determines what type of traffic is
permitted across a single connection point between networks.
A ``pure'' firewall is completely transparent in a network.
However, most firewalls are integrated into routers or gateways.
- gateway: A gateway is a special kind
of router (and often doubles, or triples as a firewall).
Sometimes, a gateway is called an ``edge router''.
A residential gateway is a combination
of router, switch and firewall. Essentially, a gateway in a
network is ``the guy to ask if the destination is not in the
local network.''
Copyright © 2005-10-06 by Tak Auyeung
