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1. ) Routing Information Protocol (Version 2) Routing Information Protocol version 2 (RIPv2) is an extension of the Routing Information Protocol (RIP), designed to increase the quantity of useful information that can be stored in messages, while adding a measure of security. This classless distance-vector routing protocol, which also uses User Datagram Protocol (UDP) port 520, was first defined in Request For Comment (RFC) 1388 (in the year 1993) and was updated in RFC 1723 (in the year 1994) and RFC 2453 (in the year 1998).

It is similar to its predecessor (RIPv1) in the following ways: updates are also sent every 30 seconds; the hop limit is also 15; triggered updates are also used, as well as UDP Port 520; split horizon with poisoned reverse is also used to prevent loops and counting to infinity; it has the same administrative distance, which is 120 on Cisco routes; it also summarizes IP networks at network boundaries; and automatic summarization can also be disabled using the no auto-summary command.

However, RIPv2 is more enhanced, with Variable-Length Subnet Mask (VLSM) and Classless Inter-Domain Routing (CIDR) support, as well as support for route authentication. RIPv2 can be used in small networks where VSLM is required, or at the edge of the larger networks. Furthermore, since RIPv2 multicasts route updates, it does send the subnet mask with route updates. While RIPv1 uses the IP address 255. 255. 255. 255 to broadcast its route updates to the other RIP routers, RIPv2 uses the IP address 224. 0. 0. 9 to multicast the router updates.

With RIPv2, authentication can be enabled on any router interface to ensure that communication only takes place with RIP routers that are part of the network. If authentication is enabled, RIP routers will only accept and process the route updates holding the correct authentication password. Although RFC 1723 describes plain text passwords for RIPv2, Message Digest (MD) 5, as defined in RFC 1321, may also protect routers against intentional misdirection by malicious users. The new implementation also includes a built-in Internet Control Message Protocol (ICMP) Router Discovery (RFC 1256) mechanism.

A maximum of 25 routes are contained in RIPv2 messages. When authentication is used, the figure is 24 routes. References: * Cisco Certification Academy (2009). Routing Information Protocol version 2 (RIPv2). Retrieved October 31, 2011 from http://www. ciscocertificationacademy. com/Routing-Information-Protocol-version2-RIPv2. php * DiNicolo, D. (2007). Routing Information Protocol Version 2 (RIPv2). Retrieved October 31, 2011 from http://www. 2000trainers. com/routing-protocols/ripv2/ * Javvin Company (2004). RIP2: Routing Information Protocol version 2. Retrieved October 31, 2011 from http://www. avvin. com/protocol/RIP2. html * Oracle Corporation (2010). Routing Information Protocol Version 2 (RIPv2). Retrieved October 31, 2011 from http://download. oracle. com/docs/cd/E19683-01/817-0493/whatsnew-updates-28/index. html 2. ) Interior Gateway Routing Protocol The Interior Gateway Routing Protocol (IGRP) is a Cisco interior routing protocol. An interior routing protocol is designed to be used within an autonomous system (the private network of an organization), as opposed to an exterior routing protocol which operates between autonomous systems. IGRP is a distance-vector protocol.

Although link-state protocols are superior because they send local information to all nodes in the internetwork, distance-vector protocols are appropriate for small internetworks, since they mathematically compare routes using some measurement of distance and require much less configuration and management. In the mid-1980’s, the most widespread interior routing protocol was the Routing Information Protocol (RIP). Although it was quite convenient for routing within small-sized to moderate-sized, relatively homogeneous internetworks, its limits were being pushed by network growth.

As a result, Cisco developed IGRP to provide a substitute to RIP. The popularity of Cisco routers and the strength of IGRP encouraged many organizations with large internetworks to replace RIP with IGRP, which at the time was a noteworthy improvement over RIP, which had a hop count restriction that limited the size of an internetwork. IGRP supports internetworks with up to 255 hops. Since RIP and IGRP are both distance-vector routing protocols, IGRP share many features in common with RIP. However, IGRP is distinct in several ways.

Upon router startup, IGRP broadcasts request messages to other routers and upon receiving the messages, these routers send their routing tables to the startup router; routing tables contain entries for each of the networks that a router can reach. At regular intervals, routers automatically send their routing tables to other routers which in turn update their own routing tables if there are changes in the topology; a triggered update occurs if the network topology changes, allowing quick responses to changes in the network.

When routers add entries to routing tables, 1 is incremented to the hop count to account for the hop between the router and the sender of the route information. Finally, when a route is entered into the routing table, a timer is set. As routing table updates reach their destination and a route entry is evaluated for its validity, the timer is reset; if a known router fails to appear in an update and in subsequent updates, the timer runs out and the route entry will be removed.

Because distance-vector routing is based on distance, a distance-vector table is built by each router that contains two primary entities: a vector (the destination) and a distance (the cost). IGRP gives more flexibility to this concept by supporting various types of cost metrics used to calculate the best route to a destination. These metrics consist of: Internetwork delay, Bandwidth, Reliability and Load. Internetwork delay is based on the delay of different types of networks and links (e. g. token ring, Ethernet, etc. ), which Cisco has predefined while Bandwidth is based on their different bandwidths.

Meanwhile, Reliability and Load both use a scale of 1 to 255, where 255 is a 100% reliable interface for the former and is a 100% reliable load for the latter. To provide additional flexibility, IGRP also allows multipath routing of up to six parallel paths. However, only routes with metrics that are within a certain range or variance of the best route are used as multiple paths. In order to address the issues of IGRP, enhanced alternatives were made: EIGRP (Enhanced Interior Gateway Routing Protocol) and OSPF (Open Shortest Path First). References: Javvin Company (2004). Cisco IGRP: Interior Gateway Routing Protocol. Retrieved October 31, 2011 from http://www. javvin. com/protocolIGRP. html * Sheldon, T. and Big Sur Multimedia (2001). IGRP (Interior Gateway Routing Protocol). Retrieved October 31, 2011 from http://www. linktionary. com/i/igrp. html 3. ) Open-Shortest-Path-First Routing Protocol The Open Shortest Path First (OSPF) is an interior gateway protocol (IGP), complex yet more efficient and faster than the Routing Information Protocol (RIP), making it an alternative routing protocol.

It is used to distribute routing information between routers belonging to a single autonomous system. The OSPF protocol was specially designed by the Internet Engineering Task Force for the Internet Protocol Suite (ISP) environment, with specific support for Class Inter-Domain Routing (CIDR) and the labeling of externally-derived routing information. It is based on link-state technology or Shortest Path First (SPF) algorithms, instead of the Bellman-Ford algorithm. Link-state routing is a substitute for distance-vector routing, an earlier routing protocol that is not as efficient when used on large internetworks.

Each router collects information on how it is linked to other routers on an internetwork, and builds a database describing the autonomous system’s topology. From this database, a routing table is calculated by constructing a shortest-path tree. This tree defines the shortest path from each router to each destination address. When there are several routes having equal costs to a destination, traffic is divided equally among them. A route’s cost is defined by a single dimensionless metric.

The main difference between RIP and OSPF is that the former only keeps track of the closest router for each destination address, while the latter keeps track of a complete topological database of all connections in the local network. OSPF offers the authentication of routing updates, and uses IP multicast when transmitting or receiving the updates. OSPF routes IP packets based exclusively on the destination IP address found in the IP packet header. Moreover, IP packets are not encapsulated in any other protocol headers as they travel the autonomous system. OSPF allows different networks to be grouped together in areas.

However, an area’s topology is hidden from the rest of the autonomous system, significantly reducing routing traffic. Also, routing within the area is controlled only by the area’s own topology, protecting the area from bad routing data. OSPF allows the flexible configuration of IP subnets. Although each route has a specific destination and mask, two different subnets of the same IP network may have different sizes (masks). This is called variable length subnetting. Furthermore, a packet is routed to the best match. References: * Colasoft Co. , Ltd. (2006). OSPF (Open Shortest Path First Routing Protocol).

Retrieved October 31, 2011 from http://www. protocolbase. net/protocols/protocol_OSPF. php * Javvin Company (2004). OSPF: Open Shortest Path First Protocol (OSPFv2). Retrieved October 31, 2011 from http://www. javvin. com/protocolOSPF. html * Living Internet (1996). Open Shortest Path First (OSPF). Retrieved October 31, 2011 from http://www. livinginternet. com/i/iw_route_igp_ospf. htm * Sheldon, T. and Big Sur Multimedia (2001). OSPF (Open Shortest Path First) Routing. Retrieved October 31, 2011 from http://www. linktionary. com/o/ospf. html 4. ) Enhanced Interior Gateway Routing Protocol

The Enhanced Interior Gateway Routing Protocol (EIGRP) or Enhanced IGRP is a proprietary Cisco classless distance-vector routing protocol utilizing the Diffusing Update Algorithm (DUAL), invented by Dr. J. J. Garcia-Luna Aceves of Stanford Research Institute (SRI) International as an improvement to the IGRP. Created especially for use in large networks, EIGRP is often regarded as a hybrid protocol because it incorporates features of a distance-vector routing protocol (advertises routes) and features of a link-state routing protocol (creates neighbor relationships).

EIGRP uses Internet Protocol (IP) 88, has the ability to support IP, AppleTalk and IPX, and is often used in Cisco-based networks running multiple network-layer protocols. Although IGRP uses the same distance vector technology as IGRP, changes were made in the convergence properties and the operating efficiency of the protocol. EIGRP can redistribute its routes and metrics into other routing protocols and accepts redistribution from other routing protocols as well. The main trouble in scaling an organizational network is managing the network overhead that is transmitted, specifically over slow WAN links.

The less the information about the network, its services and networks that need to be sent, the greater the capacity available for the data between clients and servers. While sending less routing information alleviates the network, it provides the routers less information needed to make decisions. Static and default routes may lead to poor routing decisions and the loss of connectivity. As a proprietary distance-vector protocol, IGRP has solved many of these difficulties. However, it still confronts some issues concerning scaling due to the intrinsic nature of the distance vector.

EIGRP is focused on these problems related to network scaling; it has four major constituents: the Neighbor Discovery/Recovery, the Reliable Transport Protocol (RTP), the Diffusing Update Algorithm (DUAL) Finite State Machine and Protocol-Dependent Modules. Using Neighbor Discovery/Recovery, routers dynamically find other routers running IGRP/EIGRP, form neighbor relationships and discover the state of their neighbors (may be unreachable or inoperative) using hello packets.

Using RTP, route updates are guaranteed to be transported or distributed in a reliable and dependable manner, while routing update information transported in succession is properly sorted. Meanwhile, the DUAL Finite State Machine chooses the finest successor path and the second best feasible path in reaching the destination for EIGRP, and prevents routing loops. When there is no possible path and the recipient is down, the route entry is placed in an active state. The EIGRP routers then continue to send query packets to the neighbor routers in order to discover an alternate path for the packet.

DUAL may also be used to prevent routing loops by detecting loop-free paths to the destination network. Because EIGRP is classless, Classless Inter-Domain Routing (CIDR) and Variable-Length Subnet Mask (VLSM) support the multicasting of the route updates, along with the subnet mask. EIGRP also supports route authentication using Message Digest (MD) 5. Similar to IGRP, EIGRP can only be used in Cisco routers, can load balance across equal and unequal cost paths, and summarizes at network restrictions. Unequal cost path load balancing must be configured using the variance command. References: Cisco Certification Academy (2009). Enhanced Interior Gateway Protocol (EIGRP). Retrieved October 31, 2011 from http://www. ciscocertificationacademy. com/Enhanced-Interior-Gateway-Routing-Protocol-EIGRP. php * Patterson, J. (1999). Enhanced Interior Gateway Protocol (EIGRP). Retrieved October 31, 2011 from http://www. inetdaemon. com/tutorials/internet/ip/routing/eigrp/index. shtml 5. ) Border Gateway Protocol The Border Gateway Protocol (BGP) is a classless inter-domain routing protocol used mainly for providing and exchanging network accessibility information between domains or autonomous systems.

It is also the most common exterior gateway protocol (EGP), which ensures that packets arrive at their destination network regardless of the current network conditions. It makes it possible for Internet Service Providers (ISPs) to connect with each other and for end-users to connect with more than one ISP. BGP is the only protocol that is created to deal with a network having the size of the Internet, and is the only protocol that can handle multiple connections to unrelated routing domains. It became an Internet standard in 1989 and was originally defined in Request for Comment (RFC) 1105.

The current version, BGP4 was adopted in 1995 and is defined in RFC 4271. BGP has been verified to be scalable, stable and provides the mechanisms needed to support complex routing policies. Comparable to RIP, the BGP algorithm offers immense network stability, substantiating that if one Internet network line goes down, BGP routers can immediately adjust to send packets using another connection. Used on the edge of autonomous systems, BGP is an exterior routing protocol which identifies loop-free paths across the Internet.

It uses a path-vector routing algorithm, which records the path taken in terms of the autonomous system it passes through, does not track the route through individual routers within an autonomous system, and is not particularly able to perform load balancing or packet forwarding itself. The routing protocol of choice used by all the Network Service Providers (NSPs) such as UUNet, Sprint, Cable & Wireless, Level3 and Quest, BGP is dynamic and can handle outages and link failures cautiously. BGP has undergone three amendments.

The present version (BGP4) is supported by most router manufacturers including Cisco, Lucent/Bay and Juniper, as well as by Unix and Linux programs such as Zebra. BGP uses a Transmission Control Protocol (TCP)/Internet Protocol (IP) connection to send routing updates using TCP/IP port 179. BGP can be defined as a “reliable” protocol. Although BGP version 3 supplies the dynamic learning of routes, BGP 4 includes additional route dampening features, communities, Message Digest (MD) 5 and multicasting capability. References: * Cisco Certification Academy (2009).

Border Gateway Protocol (BGP). Retrieved October 31, 2011 from http://www. ciscocertificationacademy. com/Border-Gateway-Protocol-BGP. php * Patterson, J. (1999). What is Border Gateway Protocol (BGP)?. Retrieved October 31, 2011 from http://www. inetdaemon. com/tutorials/internet/ip/routing/bgp/whatis. shtml * Living Internet (1996). BGP, Border Gateway Protocol. Retrieved October 31, 2011 from http://www. livinginternet. com/i/iw_route_egp_bgp. htm * BGP Advanced Internet Routing Resources (2002). Border Gateway Protocol. Retrieved October 31, 2011 from http://www. bgp4. as/

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