Dynamically determine the optimal route, the skillful mechanism of "routing protocol"

　The routing protocol is a protocol used by routers to exchange information.The router uses a routing protocol to exchange route information and dynamically creates and updates a routing table.Then, refer to the routing table to select the optimal route to the destination network.

　Routing protocols can be broadly divided into IGP (Interior Gateway Protocol) and EGP (Exterior Gateway Protocol).EGP is a protocol used for a routing protocol used in one AS (Autonomous System) to connect between IGP and AS.AS is a network that is managed and operated by unified policies.

　Representative IGP and EGP are OSPF (Open Shortest Path First) and BGP (Border Gateway Protocol).For this reason, most of the network specialists (Nespe) exams are taken up.

回線の帯域や信頼性を考慮

　The feature of OSPF is to consider the bandwidth and reliability of the line.When calculating the metrick, the costs are used in consideration of the type and bandwidth of the connected network.

　The cost in OSPF is the value set by the network administrator to the interface of each router, and is determined based on bandwidth and reliability.A value that adds the cost on the route is used as a metric.Then select a small route of the metric.

　For example, there are multiple routes to reach the destination network.From the router A of the source network to the router E of the destination network, there are two types: (1) router A → router B → router D → router E and (2) router A → router C → router E.

　Suppose you set the cost of the interface connected with a 100m bit/second line to "10" and the cost of the interface connected with a 1G bit/second line to "1".

　In this case, the route (2) has a smaller hop number (number of routers via), but the metric, which is the total cost of the route (1), is smaller.For this reason, OSPF selects the route (1) as the optimal route.