cisco ccna v6

cisco ccna v6.66 Chapter 1 Network Protocols and Network Device BasicsIP routing protocols can also be classified based on the algorithms used to learn routes and select the best path to the destination network, which is another common way to classify routing protocols. Commonly used algorithms for IGP protocols include the distance vector algorithm (used by RIPv2), the link state algorithm (used by OSPF and IS.IS), and the advanced distance vector algorithm (also called the hybrid algorithm, used by EIGRP).1. Distance Vector AlgorithmThe distance vector (DV) algorithm is the first algorithm used by routers to exchange routing information and is generally based on the Bellman-Ford algorithm. RIPv2 is one of the routing protocols that uses the DV algorithm and is very well known. To better understand the principles of the DV algorithm, the following two concepts are to be introduced.Neighbor is two routers or Layer 3 devices that are directly connected to each other.Hopcount is a number that represents the distance between a router and a particular network (i.e., the number of routers along the path). A router running the DV protocol will send a "distance vector" (a routing protocol message) to neighboring routers containing information about the IP networks to which the machine can forward packets and the corresponding forwarding cost.In Figure 1.59, R2 sends a message to R1 indicating that the machine can forward packets to IP network 10.0.3.0/24 with a forwarding cost of 0 (because the IP network is directly connected to the machine); it can also forward packets to IP network 10.0.5.0/24 with a forwarding cost of loR3 also sends a message to R1 indicating that the machine can forward packets to IP network 10.0.5.0/24 with a forwarding cost of 2; it can also forward packets to IP network 10.0.3.0/24 with a forwarding cost of 1. After receiving the above message, R1 updates its routing table to add both IP networks 10.0.3.0/24 and 10.0.5.0/24 as reachable via R2, because the number of routers separating R2 from those two IP destinations is 1. The number of routers between R2 and those two IP destinations is low (i.e., it costs less to forward packets to those two IP networks).The NetB 10.0.3.0/24 DV protocol has the following shortcomings. Figure 1.59 Example of exchanging distance vectors between routers1.4 Internet Protocol and Layer 3 Technologies 67Distance vectors are exchanged between routers that are neighbors of each other until all routers generate a stable routing table. At this point, the routing protocol reaches convergence. Routing protocol messages are also periodically exchanged between mutually neighboring routers. If the link between the neighboring routers is broken, both routers detect the failure and immediately notify their respective other neighboring routers. Each neighboring router will notify its own neighboring router of the failure and make the appropriate updates to the route until the routing protocol converges again.