M ODULE 1 UNIT 3 ROUTING

R OUTING Routing protocols are the set of rules used by the routers to communicate between source and destination. They do not move information to source, to destination, only update the routing table.

P ATH SELECTION Multiple path to same destination Best path is selected by the routing protocol, based on a specific value (metric) Each protocol uses its own rules and metrics to build and update routing tables Metric is used to measure the distance to the destination network Lowest metric = best path, placed in routing table

A B R1 R4 R2 R3 R6 R7 R5 R8 P ATH S ELECTION Minimum cost from A to B is 39 units

P ACKET DELIVERY Packet delivery is the physical process of transmitting the packet to the destination host.

R OUTING ALGORITHMS AND METRICS Performance Be efficient in selecting the best route Be efficient in routing packets Be reliable and flexible Support rapid convergence

T YPES OF ROUTING ALGORITHMS Hierarchical – in hierarchical routing systems, certain routers form a routing backbone Host-intelligent – it assumed that end systems (hosts) can perform path determination and routers act as store-and-forward devices only.

T YPES OF ROUTING ALGORITHMS CONT ’ D … Distance vector – uses simple algorithms that calculate distance value between routers based on hop count. Example Routing Information Protocol (RIP) Interior Gateway Routing Protocols

T YPES OF ROUTING ALGORITHMS CONT ’ D … Link State Routing Protocols – uses sophisticated algorithms that maintain a complex database of internetwork topology Example Enhanced Interior Gateway Routing Protocol Open Shortest Path First

R OUTING METRICS Bandwidth – Throughput speed in bits per second Cost – An arbitrary value assigned by an administrator for the intersecting of networks Delay – Network latency caused by such factors as distance or congestion Hop Count – The number of network layer devices along with the path

R OUTING METRICS CONT ’ D … Load – a metric that bases routing decisions on how busy a particular route is. MTU (Maximum Transmission Unit) – The largest unit size allowed to be transmitted on all routes from source to destination Reliability – Represents the amount of network downtime, that is, how reliable a network path is)

RIP (R OUTING I NFORMATION P ROTOCOL ) Uses Distance Vector Routing approach Each node exchanges information with neighbors Directly connected by same network Each node maintains three vectors Link cost One entry for each network it attaches Distance vector ( metric column in the next slide) Current cost of route from the node to each destination network in the configuration Next hop vector ( Next router column in the next slide) The next router for each destination network in the configuration Every 30 seconds, exchange distance vector with neighbors Use distance vectors received from neighbors to update distance and next hop vector Similar to Bellman-Ford algorithm. Routing table

R OUTING PROTOCOLS CONT ’ D … Enhanced Interior Gateway Routing Protocol (EIGRP) works on any condition It supports the features both distance vector & link state protocol. EIGRP is an ideal protocol in the large networks.

R OUTING PROTOCOLS CONT ’ D … Each router stores information in three tables: Neighbour Tables Each router keeps state information about adjacent neighbours. When newly discovered neighbours are learned, the address and interface of the neighbour are recorded The topology table contains all destinations advertised by neighbouring routers. Associated with each entry are the destination address and a list of neighbours that have advertised the destination.

R OUTING PROTOCOLS CONT ’ D … Routing table – stores the routes selected by DUAL as the best ones

O PEN S HORTEST P ATH F IRST (OSPF) RIP is limited in large internets OSPF is preferred interior routing protocol for TCP/IP based internets Link state routing used

R OUTING PROTOCOLS CONT ’ D … Each router sends that portion of the routing table (keeps track of routes to particular network destinations) that describes the state of its own links, and it also sends the complete routing structure (topography).

B ORDER G ATEWAY P ROTOCOL (BGP) For use with TCP/IP internets Preferred ERP of the Internet Allows routers (gateways) in different Autonomous Systems to exchange routing information Current version is BGP-4 RFC 4271 No time to cover

I PV 4 AND IPV 6 INTERNET ROUTING Features of IPV4… Connectionless protocol and best effort based. Simplicity It is simpler and easy to remember Require less memory Familiarity Millions of devices are already knowing it Existing infrastructure already support it

B ENEFITS OF IPV4…. Widely support Shorter & Sweeter (header) Support of all Operating Systems All commonly used protocols are supported

S HORTCOMING OF IPV4…. IPV4 specification didn’t identify any security mechanism. Millions of class A addresses are wasted. Many class B addresses also wasted. Not so many organizations are so small to have a class C block. Class E addresses were reserved for future purposes.

IPV4 S UPPORTING D EVICES.. PCs Servers Modems Routers Printers Cameras Smart Phones Tablets & Gaming Systems Just about anything else connecting to the Internet

W HY IPV6…..? IPV6 provides a platform on new internet functionality that will be needed in the immediate future and provide flexibility for future growth and expansion.