Ethernet Basics – 8 Routers

Routers and Routing Definition of a router- A device which provides a path from a node on one network or subnet to a node on another network Definition of routing- the process of determining and end-to-end path between the sender and the receiver of a packet. There are 2 types: –Source routing- the source node determines the route and includes it in special fields in the data frame. Source route bridging in Token Ring uses source. –Hop-by-hop- The route between source and destination is determined along the way, hop by hop. Most routing protocols are hop-by-hop based. The routing protocols most used are RIP, RIPII and OSPF for standard protocols. They will be discussed in greater detail during the Routing/Layer 3 presentation

Routers A router has 2 main functions: –Connect networks together –Block broadcasts All the other functions that we have seen routers do are add-ons and are not part of the root functionality For routers to learn where the different networks are located within an area, a routing protocol is used to tell routers what network is off what router. There are 2 ways to do this… –Static- you manually script on each router where all the networks are. This is very time and maintenance intensive –Dynamic- the routing protocol itself learns the attached networks and sends this information automatically between all the routers. Routing Table- This table holds all the IP/Network layer information for the router much like the forwarding database on a switch holds the layer 2 location information for end devices. It also called an ARP cache for end device information.

Router- Network Layer

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