Kazi Fall 2007 CSCI 370/EENG CSCI-370/EENG-480 Computer Networks Khurram Kazi

Kazi Fall 2007 CSCI 370/EENG Major sources of the slides for this lecture  Slides from Tanenbaum’s and William Stallings’ website are used in this lecture  Interworking with TCP/IP, M , Global knowledge, training manual, (  Teach yourself TCP/IP in 24 hours, Joe Casad, Bob Willsey, SAMS  The Internet and Its Protocol, Adrian Farrel’s book.

Kazi Fall 2007 CSCI 370/EENG Reference Network: For discussion purposes

Kazi Fall 2007 CSCI 370/EENG Implementation of Connectionless Service Routing within a diagram subnet.

Kazi Fall 2007 CSCI 370/EENG Implementation of Connection-Oriented Service Routing within a virtual-circuit subnet.

Kazi Fall 2007 CSCI 370/EENG Comparison of Virtual-Circuit and Datagram Subnets 5-4

Kazi Fall 2007 CSCI 370/EENG Routing Algorithms The Optimality Principle Shortest Path Routing Flooding Distance Vector Routing Link State Routing Hierarchical Routing Broadcast Routing Multicast Routing Routing for Mobile Hosts Routing in Ad Hoc Networks

Kazi Fall 2007 CSCI 370/EENG Routing  Routing and forwarding is what the Internet is all about  How can an IP packet from one host be delivered to the destination host?  Within an individual router lies the answer: Routing Table  Routing table maps the destination address carried in a datagram to the address of the next hop along the path (next hop address) and the interface through which the datagram should be forwarded (the outgoing interface)

Kazi Fall 2007 CSCI 370/EENG Routing  In simple networks, routing table can be manually configured or learned from the configuration of interfaces on the router.  In complex networks where there are many routers arranged in a mesh with lots of links between routers, each having different capabilities, manual configuration becomes onerous/troublesome.  Even more important is when there are changes in the network – how do other routers are informed of such changes and how they react to the change.  e.g. Link failure, routers added to the network  Routing protocols are used to collate and distribute information about the network connectivity  Once the connectivity information has been distributed the question of how to compute the best path still remains.  Routing algorithms can be run against the view of the network to determine the best path along which to forward the datagram.

Kazi Fall 2007 CSCI 370/EENG Routing  Routing Information Protocol (RIP) is simple and ubiquitous.  Open Shortest Path First (OSPF) protocol is very popular and has a close rival, Intermediate System to Intermediate System (IS-IS), that performs a similar function  Border Gateway Protocol (BGP) is important for hooking together the many Service Provider networks into a single Internet

Kazi Fall 2007 CSCI 370/EENG Classless Interdomain Routing (CIDR)  Last lecture: IP addresses are grouped in classes  Different nibbles/bytes split the address into network portion and the host portion of the IP address  Network mask indicates the length of the network part of the address – know as prefix length  Earlier networks routed traffic based on the classes (A, B or C type)  Subnetting allows the networks to be divided into smaller segments  Subnetting process defines range of addresses assigned to a subnet according to prefix length  Routing using subnetwork addresses is not quite simple as routing as using class addresses, because knowledge of the network mask (prefix length) is not encoded in the address itself  Routing table must consist of a list of subnetwork addresses (i.e. addresses and prefix length), each mapping to a route or path along which packet for that subnet should be forwarded  Routing table will explode if all addresses have to be included in the routing table. e.g., in class A potentially there are bit prefix subnetworks  The solution within the Internet is to route at an appropriate level of granularity through address aggregation

Kazi Fall 2007 CSCI 370/EENG Route address aggregation SubnetworkSubnetwork MaskAddress Range / – / – / – The subnet addresses can be combined/aggregated as a single subnetwork /26

Kazi Fall 2007 CSCI 370/EENG Simple network showing a multi-access link, a numbered point-to-point link and an un-numbered link Numbered link Loop back address is known as a routable router identifier because it is an IP address that can be installed in the routing tables at other routers

Kazi Fall 2007 CSCI 370/EENG Distance Vectors

Kazi Fall 2007 CSCI 370/EENG Routing Table at Router E. Initial routing Distribution while the link between Routers A and B Disabled DestinationOutgoing Interface DistanceNext Hop E B B F F C B D F A 3F

Kazi Fall 2007 CSCI 370/EENG Routing Table at Router E. After Full Distribution DestinationOutgoing Interface DistanceNext Hop E B B F F C B D F A 2B