See also: [Hub], [Switch], [Routing]



'''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 [Subnet Subnets] 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.



If you run [Windows] you can control your routes using the ''route'' command at a DOS prompt. ''route print'' will show your routing table.



If you run Linux you should be able to control your routes using ''route'' or ''ip''.  Issuing a ''route'' or ''ip r'' at the command prompt should show your routing table.



[Broadband] or [ADSL] Routers are common examples of routers designed for the home market.  They allow you to run a home [LAN Local Area Network] and let any device on that LAN access your Broadband Internet connection.  Broadand Routers usually also have [Firewall] and other capabilities



'''Note:''' A device that links two parts of a network together that are physically different medium eg [FibreOptic] and [Cat5] [Ethernet] or [Cat5] and [802.11b] Ethernet is generally not considered to be a Router unless it also routes traffic between two networks or [Subnet Subnets].  A device that links two or more network protocols (such as [TCPIP TCP/IP], [IPX] or [AppleTalk]) is these days known as a [Gateway].