Dynamic Routing: Dynamic routing protocols can dynamically respond to changes in the network. The routing protocol is configured on each router and the routers learn about both each other and remote networks. Examples of modern dynamic routing protocols include: • RIP v1,2 • EIGRP • IS-IS • OSPF • BGP Dynamic Routing Protocols could be “IGP” or “EGP” Interior Gateway Routing (IGP) Protocol: Used for intra-As routing that is routing inside an AS. Exterior Gateway Routing (EGP) Protocol: Used for inter-As routing that is, routing between autonomous systems. What is an Autonomous system? An AS is a collection of routers under a common or technical administration that represents a common, clearly defined policy for the internet. Dynamic Routing Protocols have classed into three different classes: 1. Distance vector 2. Link state 3. Hybrid Distance Vector routing protocols: Distance vector means that routes are advertised as vectors or distance direction. Distance is defined in terms of a metric such as hop count, and direction is the next hop router or exit interface. Distance vector protocols typically use the bellman-ford algorithm for the best route determination. Some distance vector routing protocols periodically send complete routing table to all connected neighbors. In large networks these updates can be an issue. The bellman-ford algorithm needs enough knowledge to maintain a database of reachable networks, the algorithm does not allow a router to know the exact topology of an internetwork. The router only knows about the information that it receives from its directly connected neighbors. The only information that router knows about a remote network is the distance or metric to reach that network and which path to interface to use to get there. Distance vector routing protocols do not have the actual map of the network topology. Distance Vector routing protocol works well in situations where: 1. The network is simple and flat and does not have a hierarchical design. 2. The administrators do not have enough knowledge to configure and troubleshoot link state routing protocols. 3. Specific types of networks, such as hub-and-spoke networks, are being implemented. 4. Worst-case convergence times in a network are not concern. Link State Routing Protocol: In contrast to distance vector routing protocol a router configured with a link state routing protocol can create a “complete view” or topology of the network by gathering information from the other routers. Think of a like state routing protocol as having a complete map the network topology. A link state router uses the link state information to create a topology map and select the best path to all destination networks in the topology. Link state routing protocols do not send periodic updates of their routing tables to their neighbors after the network is converged. They send triggered updates as a link state update packet when there is a change in the topology. Link state routing protocols work best in situations where: 1. The network design is hierarchical usually used in large networks. 2. The administrators have a good knowledge of the implemented link state routing protocols. 3. Fast convergence of the network is crucial. Examples: 1. OSPF 2. IS-IS Hybrid/Advanced Distance Vector Advanced distance vector is the title Cisco gives to EIGRP, which borrows the best attributes of both distance vector and link state designs. EIGRP does not send periodic route information; instead it sends updates only when changes occur (like link state protocols). Also, EIGRP forms neighbor relationships with its directly connected peers and only updates them – not the entire network (like distance vector protocols).
Posted on: Sun, 02 Nov 2014 12:22:18 +0000
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