[bs_icon name=”glyphicon glyphicon-chevron-right”]  The Purpose and Properties of Routing

• Interior Gateway Protocol (IGP) – routing protocol that is used within an autonomous system which is sometimes referred to as an administrative domain. One type of Interior Gateway Protocol are the Distance-vector routing protocols such as Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP) and Enhanced Interior Gateway Routing Protocol (EIGRP). Another type are the Link-state routing protocols such as Open Shortest Path First (OSPF) and Intermediate system to intermediate system (IS-IS)
• Exterior Gateway Protocol (EGP) – routing protocol that is used across different autonomous systems / administrative domains. It was the routing protocol leveraged for Internet connected devices in the early 1980s. Border Gateway Protocol (BGP) is the replacement standard for Internet routing over EGP.
• Static Router Updates – a router with manually configured routing tables. For these types of devices, a network administrator will manually build and make updates to the routing table for all routes in the administrative domain. Static routers are best suited for small internetworks; due to the need of the manual administration, they do not scale well to large networks where routing information is often changed, updated and appended. Static routers are not fault tolerant because when another network device goes down the manually input information may not necessarily provide alternate pathing to a destination which makes it unreachable (unless quick, manual administrative updates are made.)
• Dynamic Router Updates – A router with dynamically configured routing tables. This type of automatic configuration is made up of routing tables that are built and maintained by ongoing communication between the routers only (by default – this does not include initial setup and configuration or administrative needs for a persistent route configuration). Dynamic routing is fault tolerant; if a router or link goes down, the routers sense the change in the network topology when the “learned route” expires in the routing table and cannot be renewed due to the outage. This change is then disseminated to other routers so that all the routers “learn” of the network changes. Routing Information Protocol (RIP) and Open Shortest Path First (OSPF) routing protocols for IP and RIP for IPX are some of examples of protocols that can be used for these dynamic updates.
• Next Hop – defined as the next place that a data packet needs to go. In most cases, routers do not need all of the information regarding where the originating source of the data transmission was. In most cases routers just need to know where there data needs to go next and the “next” referred to as the “next hop” because all they are trying to do is deliver it to the specified destination IP address that is included in the header information of the data being sent. If that router is the last hop and can deliver it to the specified IP address it does otherwise it refers to its routing tables to figure out which router to hand it off to in the effort to get the data packet where it needs to go.
• Routing Tables – sometimes referred to as a Routing Information Base (RIB), is the database information that stores all the rout information for the routing network devices. The routing table holds the route information regarding the topology of the network immediately around the device to other network destinations and it will often include the metric / cost associated for the route. There are three main route entries that are generally found in the routing tables – Network Route, Host Route and the Default Route. The Network Route is route to a specific Network ID on the network. The Host Route is a route to a specific network address. A Default route is the path used if a physical router or other network routing device cannot find a route for the specified destination.
• Convergence – achieved when all of the available topology information from routing devices have been passed along to all of the other deceives in totality and all when the information gathered is not in a contradiction state to any other router’s informed topology information. When all of the network routing devices “agree” on what the network topology looks like it is said to have full convergence.

**Source by wikipedia**

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