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Spelling: Router
See also: Hub [1], Switch [2], Routing [3]
Also known as a Gateway [4]
A ROUTER IS AN INTELLIGENT DEVICE THAT LINKS TWO OR MORE COMPUTER
NETWORKS TOGETHER.
Generally (see note below) this means that it links two subdivisions
or Subnets [5] of a TCP/IP network together.
A router can be a dedicated device or it can be a normal PC with two
or more network cards. It operates a bit like a postal exchange.
Network data is sent as PACKETS. Each packet contains information as
to its destination. A router will read the destination of every packet
it receives and work out where to send it. It does this by consulting
its ROUTING TABLE. The Routing Table is a list of destination network
addresses and/or subnets. In this list each destination is
cross-referenced to one of the router's network interfaces and the
address of the next router on the path to that destination. The router
does not "know" the entire delivery path or _'Route_ of the data. It
simply "knows" that by sending the data to the appropriate interface
it will get to its destination.
Routers often have a DEFAULT ROUTE (sometimes called a DEFAULT
GATEWAY in their Routing Tables. If the router receives a packet that
is destined for an address that is not in its Routing Table, the
router will send that packet to the DEFAULT GATEWAY, if it has one. If
the router does not have Default route and it does not "know" where to
send the packet, it will send a DESTINATION HOST UNREACHABLE or
similar message back to the sender.
NOTE: A device that links two parts of a network together that are
physically different medium eg FibreOptic [6] and Cat5 [7] Ethernet
[8] or Cat5 [9] and 802.11b [10] Ethernet is generally not considered
to be a Router unless it also routes traffic between two networks or
Subnets [11].
Links:
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[1] http://melbournewireless.org.au/?Hub
[2] http://melbournewireless.org.au/?Switch
[3] http://melbournewireless.org.au/?Routing
[4] http://melbournewireless.org.au/?Gateway
[5] http://melbournewireless.org.au/?Subnet
[6] http://melbournewireless.org.au/?FibreOptic
[7] http://melbournewireless.org.au/?Cat5
[8] http://melbournewireless.org.au/?Ethernet
[9] http://melbournewireless.org.au/?Cat5
[10] http://melbournewireless.org.au/?802.11b
[11] http://melbournewireless.org.au/?Subnet
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