Networking and internetworking devices

Repeater

Hub

Function of a bridge

Regenerate and filter traffic

Check destination address

Forwards the new copy to the segment towhich the address belongs

Multiport bridge

Connecting LAN segments in two buildings

Router

Gateway

Gateway is a protocol converter

IBM

Novell

Switch

Backbone

Routing algorithms

• Calculate the shortest path between two routers– Distance vector routing– Link state routing

In distance vector routing, each router periodically shares its knowledge about the

entire network with its neighbors

Network ID Cost Next Hop(ID of the next router)

The cost is base on hop count1= No hop

Routing table

14 155 1 + 1 hop

14 2 B55 2 B

14 1 14 2 B23 1 55 2 B78 114 1 23 1 55 2 B78 1

A’s new table

Final routing table

In link state routing, each router shares its knowledge of its neighborhood with all

routers in the internetwork• Flooding router sends its info.

to all of its neighbors, each neighbor sends the packet to all of its neighbors, and so on.

• Link state packet (LSP)Advertiser IDDestination network IDCostNeighbor ID

Initialization• Each router sends a short

greeting packet to its neighbor• Prepare an LSP, Floods the

network• Every router receivers every

LSP , Puts the info. Into a Link state

database

Flooding of A’s LSP

Every router has the same Link state database

Dijkstra’s Algorithm

• finds shortest paths from given source node s to all other nodes

• by developing paths in order of increasing path length

• algorithm runs in stages. each time adding node with next shortest path

• algorithm terminates when all nodes processed by algorithm

Link state routing table for router A โดยใช้� Dijkstra Algorithm

Link state routing table for router A

Bellman-Ford Algorithm

• find shortest paths from given node subject to constraint that paths contain at most one link

• find the shortest paths with a constraint of paths of at most two links

• and so on 

Example of Bellman-Ford Algorithm