Introduction to Routing and Routing Protocols By Ashar Anwar
Objectives Routing Static and Dynamic Routing Dynamic Routing Protocols Distance Vector and Link state Routing Protocols
What is Routing? Routing is the process of moving information (data packets) from one network to another network using routers. Internet is composed of multiple physical networks interconnected by routers. Both host and router participate in routing a packet to its destination. – The host must make the initial routing decision when it chooses where to send the packet.
Function of a Router Data is sent in form of packets between 2 end devices Routers are used to direct packet to its destination
Static Route A manually configured route used when routing from a network to a stub network
To view Static Routes in Routing Table Static route includes the network address and subnet mask of the remote network, along with the IP address of the next-hop router or exit interface. Static routes are denoted with the code ‘S’ in the routing table R1# show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP Gateway of last resort is not set C 192.168.1.0/24 is directly connected, FastEthernet0/0 C 192.168.2.0/24 is directly connected, Serial0/0/0 S 192.168.3.0/24 [1/0] via 192.168.2.2 Static Route
Static Routing Advantages of static routing – -Easy to configure – -No extra resources are needed – -More secure Disadvantages of static routing – -Network changes require manual reconfiguration – -Does not scale well in large topologies
Dynamic Routing Dynamic Routing involves a Routing Protocol which does: – Exchange of routing information between routers – Dynamically learns information about remote networks – Determines the best path to each network Adds routes to routing tables – Automatically learns about new networks – Automatically finds alternate paths if needed (link failure in current path)
Dynamic Routing Protocols Components of a routing protocol – Algorithm In the case of a routing protocol algorithms are used for facilitating routing information and best path determination – Routing protocol messages These are messages for discovering neighbors and exchange of routing information
Classifying Routing Protocols Dynamic routing protocols are grouped according to characteristics.
Classifying Routing Protocols Distance vector – Routes are advertised as vectors of distance & direction. – Incomplete view of network topology. – Periodic updates. Link state – Complete view of network topology is created. – Updates are not periodic.
Routing Protocols Metrics – A value used to determine which routes are better than others. – It is quantitative value used to measure the distance to a given route.
Distance Vector Algorithm Distance vector algorithms (also known as Bellman-Ford algorithms) call for each router to send all or some portion of its routing table only to its neighbors. Distance vector algorithms perform routing decisions based upon information provided by neighboring routers. Distance vector protocols use fewer system resources but can suffer from slow convergence and may use metrics that do not scale well to larger systems.
Link-State Routing Protocols Reputation of being much more complex than their distance vector counterparts. – Functionality and configuration is complex than distance vector – Algorithm is complicated than distance vector
Link-State Routing Protocols Distance vector routing protocols - road signs – Distance and vector Link-state routing protocols - road map – Topological map used by each router – Each router determines the shortest path to each network