Static And Dynamic Routing Computer Science Essay

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Static routing is a data communication concept that describes one of the two ways to configure the path selection of routers in a network. Static routing consists on manually adding routes to the routers in a network. It is possible to design and run a network completely on static routing however it is not fault tolerant. This means that if a fault arises in a certain rout, traffic will stop and until either the fault is fixed or another route is manually provided by the network administrator. With this in mind there are some cases where static routing is desirable such as "default routes".

In the figure showed above. The two LANs (Ryde and Newport) are connected to each other via WAN. Also the have an Ethernet network tied to each router. This is a prime opportunity to use Static Routing to enhance network performance. By entering just one route in each router the routing configuration will be complete. This means that all traffic directed to the network in either end of the router will have to travel on the given route. This also helps to reduce network overhead hence increasing its bandwidth.

The second way for routers to select a path on a network is called Dynamic Routing. Dynamic Routing consist on generating a series of routes to a destination node automatically from know routes. Dynamic routing is fault tolerant which makes it highly effective in large networks so if a network segment is changed or fail it does not affect the flow of traffic as there will be other routes around the failure. Dynamic routing uses several protocols to achieve hence increasing overhead in the network. Some of the protocols used on Dynamic Routing are:

Routing Information Protocol (RIP): distance vector routing protocol that uses the hop count as a routing metric and prevents routing loops by setting up a limit on the number of hops allowed in a path from source to destination (Time-to-Live).

Open Shortest Path First (OSPF): dynamic routing protocol for IP networks. It uses link state routing algorithm and operates is classed as an interior routing protocol that operates within a single autonomous system.

Intermediate System to Intermediate System (IS-IS): routing protocol design to create routes in within a group physically connected computers or similar devices by determining the best route for datagrams through a packet-switched network.

Interior Gateway Routing Protocol (IGRP): is it a Cisco proprietary distance vector interior routing protocol. It is by routers to exchange data in an autonomous system.

On the example given above, we can see how…

Question 2

Distance Vector and Link State Routing

Distance Vector Routing Protocol is one of the two major types of routing protocols on a packet-switching network. As the name implies, the routes are broadcast as vectors of distance and direction where distance represents the cost of reaching a destination (hop count) and Vector is the direction to which the packets are send to which for a router means the next-hop address and destination address. To determine which route is the best path Distance Vector Routing Protocol uses the Bellman-Ford and Ford-Fulkerson algorithm.

The second type of routing protocols on a packet-switching network is called Link State Protocol. The Link State Protocol is performs by every switching node in a network (routers for example forward packets to the internet). This type of protocols enable the nodes to create a graph of it's connectivity to the network showing which nodes are connected to other nodes. Each node then separately calculates the next best route to every possible destination in the network, this collection of "route" is called a Routing Table.

As defined above the two types of routing protocols used in packet-switching networks, there are stark differences between them. One of such differences is the way each protocol chooses the best path. While Distance Vector Protocols will prioritize the metric distance between the sending and the receiving nodes (by using path with the shortest hop count), Link State Protocols will analyse every possible route available to the destination node and will choose the one with faster time of arrival depending on the medium in spite of a higher hop count. As a result Link State Protocols are better suited for networks in which multiple types of medium are used with different transfer speed and bandwidth. However if the same type of medium is used in a network and medium speed is not a factor, Distance Vector Protocols are better suited because since medium speed is constant, hop count will significally impact the speed of data transfer. Another big difference between these two types of protocols is the way the Routing table is populated. Distance Vector type protocols every node share its routing table with other "adjacent" nodes in its network, and the Link State type protocols only share information regarding connectivity.

Question 3

Routing Information Protocols v1, v2 and Enhanced Interior Gateway Routing Protocols

As briefly explained in question 1, Routing Information Protocol (RIP) is a distance vector type of dynamic routing protocol that uses the hop count as a routing metric to determine the best path. It. Hendrick from Rutgers University in June 1988 and it is now the most widely used protocol for internet routing within networks. Since its initial development in 1988 there has been at least two versions published.

Routing Information Protocol v1: this was the original version developed by C. Hendrick in 1988 and was based on a computer program called "routed". Because it was developed during the early days of IP protocols, it uses classful routing. This means that routing updates do not carry subnet information, and have no support for variable length subnet masks thus making it impossible to have different sized subnets in the same network class. It also lacks support for router authentication making it very sensible to external attacks. RIP v1 has a limit of 16 hop counts between two routers.

Routing Information Protocol v2: because of the weakness and vulnerabilities of the original version RIP v2 was developed in 1993. This new version does indeed support Classless Inter-Domain Routing (CIDR). As the original version, RIPv2 remain a distance vector protocol and uses hop counts to determine the best path (Hop count limit remain at 16 to keep compatibility). Because RIPv2 is classless, its supports the use of variable lengths subnet masking. Unlike RIPv1, RIPv2 does not broadcast table updates but multicasted by using the address Another major flawed was corrected in this version and it is the capability of router authentication to increase security.

Enhanced Interior Gateway Routing Protocol: it is a loosely based version of the Cisco Propriety protocol IGRP. As the original version, it is also a distance vector type routing protocol. It increases routing stability after topology changes and also increases the use of bandwidth and processing power of the router.

Setting up commands and troubleshooting


REQUEST (1)- Request either a partial or full table update from another RIP router.

RESPONSE (2) - A response to a request. All route updates use this command in the command field.

TRACEON (3) / TRACEOFF (4) - Obsolete and ignored.

RESERVED (5) - Sun Microsystems uses this field for it's own purposes.

VERSION field - Describes which version of the RIP protocol it is (1 or 2).

ADDRESS FAMILY ID - Identifies which addressing protocol is being used (CLNS, IPX, IP etc.)

METRIC - Metric measures how 'good' a route is. RIP uses the number of hops as the metric. The route with the fewest number of hops is preferred.