NETWORK TUTORIALS: Routers

Determine the best path for sending data and filtering broadcast traffic to the local segment. They DON'T pass on broadcast traffic
work at the Network layer of OSI => they can switch and route packets across network segments
They provide these functions of a bridge

all known network addresses
how to connect to other networks
possible paths between those routers
costs of sending data over those paths
not only network addresses but also media access control sublayer addresses for each node

REQUIRE specific addresses: they only understand network numbers which allow them to talk to other routers and local adapter card addresses
only pass Packets to the network segment they are destined for.
routers don't talk to remote computers, only to other routers
they can segment large networks into smaller ones
they act as a safety barrier (firewall) between segments
they prohibit broadcast storms, because broadcasts and bad data aren't forwarded
are slower than most bridges
can join dissimilar access methods: a router can route a packet from a TCP/IP Ethernet network to a TCP/IP Token Ring network

Routers don't look at the destination computer address. They only look at the NETWORK address and they only pass on the data if the network address is known => less traffic

Choosing Paths

routers can choose the best path for the data to follow
routers can accommodate multiple active paths between LAN segments. To determine the best path, it takes these things into account:

If one path is down, the data can be forwarded over on alternative route
routers can listen and determine which parts of the network are busiest.
it decides the path the data packet will follow by determining the number of hops between internetwork segments

Static - manually setup and config the routing table and to specify each route
Dynamic

Distinguishing between Bridges and Routers
Both bridges and routers

recognizes the address of EACH computer on it's segment and forwards packets on the basis of the destination address
either recognizes the address or it doesn't, and forwards the packet accordingly
forwards all broadcast messages to all ports, except to the port from which the broadcast message came. Every computer on every segment receives this broadcast

works at the NETWORK layer and thus takes more information into account when determining what to forward and where to forward it to.
Routers recognize the addresses of other routers and determine which packets to forward to which routers

Multiple Paths-- important

Bridges recognize ONE PATH between networks
Routers can search between multiple paths and determine the best path at the moment

The 4 KEY pieces of information that distinguish bridges and routers:

Bridges	Routers
recognize the MAC sublayer addresses (i.e. the addresses of the network cards on its own segment)	Routers recognize network addresses not individual computer addresses
forwards everything it doesn't recognize and forwards all addresses it knows, but only out the appropriate port	routers filter addresses. It forwards particular protocols to particular addresses (other routers) if the router doesn't recognize a destination address, the packet is usually discarded
works with all protocols	only works with routable protocols Non-Routable = NetBEUI, DLC, LAT

Because they make path choices and filter out packets the segment doesn't need to receive they

Because is works at the network layer, a router can connect networks that use

Different architectures
Different media access control methods -- for example, they can connect an Ethernet segment to a Token-Ring segment

Summary of Router features

NETWORK TUTORIALS