Routing Protocols

The purpose of this document is to explain different routing protocols by using them within a scenario of being charged to reconfigure a company’s network. In the past static routes have been used and, for the scenario, I would like to ease the configuration of routing information. I am concerned about processor utilization if dynamic routing protocols are used. Also the reduction of network utilization by routing protocols is desired, as well as, ensuring the shortest path is the path taken all while preventing routing loops.
[Introduction and background]
I have been charged with the task of reconfiguring my company’s network which has grown considerably over the past year. Previously static routes have been used, but I do not wish to maintain the static routing tables since the network has grown. I would rather use a dynamic routing protocol to cause me the least amount of administrative work as possible, however I do have some major concerns. I would like to automate the updating of router table information, but I do not want this to put a major burden on my networking devices processor, memory, and I do not want this automation to place a burden on my network bandwidth. I also wish to ensure packets are being sent along the truest shortest path and in the process, avoid causing any routing loops. Finally I would like to ensure I have redundant links, so that in the event of a failure traffic will still be able to be passed via the shortest path. I am going to draw a conclusion about which dynamic routing protocol will best suite my needs by thoroughly assessing the different types of dynamic routing protocols based upon my requirements.
[Comparison of routing protocols: memory, processor, and network bandwidth usage]
There are different link-state routing protocols and it is important to know each one. Open Shortest Path First (OSPF) is a link-state routing protocol that utilizes route tables, topological databases, and the shortest path first algorithm to determine the most ideal path to send data along. OSPF uses only the destination address of a packet to determine the best route. Because OSPF maintains routing tables and topological databases it can quickly determine if a link should happen to go down and therefore reduces the processor and bandwidth overhead needed for passing routing information. OSPF maintains neighboring relationships between routers in which “hello packets” are exchanged during a handshaking by each router. This handshaking is when routers will send any updates to their routing table. Another link-state routing protocol is the Intermediate System to Intermediate System (IS-IS) routing protocol. The IS-IS routing protocol is similar to OSPF, however it is an interior gateway protocol. This means that it does not route information to external autonomous systems, and therefore relies on an exterior gateway protocol to talk between different autonomous systems (Martey, 2002). The IS-IS protocol is also not an Internet standard and also is not as widely used as OSPF. The IS-IS protocol functions at the networking layer of the OSI model, which is at the same layer as IP traffic, but it does not use IP to carry routing information messages. OSPF, on the other hand, functions at the networking layer, but it functions on top of IP allowing it to use the Internet Protocol to carry routing information messages. OSPF and IS-IS are routing protocols that are similar, however OSPF is the most widely used routing protocol and it can function on top of the Internet Protocol.
There are different distance-vector routing protocols and it is important to know about each one. The routing information protocol (RIP) is a distance vector protocol which uses hop-count as a routing metric and it relies on information from other routers to attempt to determine the best routing path. RIP allows for a 15 maximum hop count and it sends complete routing table updates to other routers every 30 seconds. Cisco has developed a proprietary distance-vector routing protocol called “Interior Gateway Routing Protocol (IGRP).” This routing protocol uses the distance-vector algorithm with the conjunction of four elements, bandwidth, delay, load, and reliability, to determine the best path for routing packets. IGRP sends routing information to other routers on the network every 90 seconds and can become both a burden on network bandwidth and processor utilization as it is updating routing information in 90 second intervals. Although, IGRP is better than RIP, it too can use some improvement. Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco proprietary protocol, however it is not the same as IGRP. EIGRP is a balanced network protocol that uses a hybrid of both the link-state and distance vector routing algorithms. This has many benefits as it provides an equal-cost load balancing, incremental routing updates, and formal neighbor relationships (Lammel, Barkl, 2003). EIGRP is similar to IGRP as it uses the same distance-vector information as IGRP, but it puts a different algorithm against that information. EIGRP uses a diffusing update algorithm (DUAL) to calculate different metrics. Distance-vector routing protocols rely on information from other routers, which is sent out in 30 second intervals, to determine the most ideal path for passing traffic.
[Distance vector protocols versus link state protocols]
When considering which dynamic routing protocol is best to use for reconfiguring a network, it is important to know about routing protocols. Routing protocols are a set of protocols that have a specific function. Routing protocols main function is to maintain route tables that are used by routers and make decisions based upon those routes (Lammel, Barkl, 2003). There are two major categories of routing protocols: Link-state and Distance-vector. A link-state routing protocol understands an entire network, it does not listen to secondhand information, and it can make advanced routing decisions. A distance-vector routing protocol only understands the distance and direction to a network connection and it listens to secondhand information in order to get its routing table updates. Link-state routing protocols will send routing information to other routers during a handshake period of communication. This allows for less CPU utilization and less bandwidth needed because link-state routing protocols only update routing tables that have changed. Distance-vector routing protocols rely on information from other routers so they will periodically send routing tables to other routers, which in the even of a connection going down can slow down a network because all networking devices using distance-vector routing will send information to each other. There are two different types of routing protocols, link-state and distance-vector, that both have their advantages, disadvantages, and proper uses.
[Recommended Protocol]
Both the link-state and the distance-vector routing protocols have advantages and disadvantages, however it is the advanced metric calculating and hybrid of both link-state and distance-vector that allows for the Cisco proprietary EIGRP routing protocol to be the most ideal dynamic routing protocol to best suite my requirements and allow for the reconfiguring of the network.
In conclusion, both link-state and distance-vector routing protocols had their uses, however it is the hybrid of both of these two routing protocols which will be the most ideal solution for my reconfiguration of my company’s network. Link-state routing protocol is efficient in identifying the most ideal routes by talking with other routers and sharing if a connection goes down. Distance-vector was one of the first routing protocols used, however its lack of efficiency and relying on outside sources to pass traffic with the high overhead needed makes it not a viable solution to suite my needs.
1. Lammel, Barkl, Todd, Andy (2003). CCDA Cisco Certified Design Associate. Alameda, California: SYBEC Inc..
2. Martey, Abe (2002, May 17). Integrated IS-IS Routing Protocol Concepts. Retrieved September 21, 2008, from Integrated IS-IS Routing Protocol Concepts Web site:

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