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A routing protocol specifies how routers communicate with each other to distribute information that enables them to select paths between nodes on a computer network. Routers perform the traffic directing functions on the Internet; data packets are forwarded through the networks of the internet from router to router until they reach their ...
The link-state protocol is performed by every switching node in the network (i.e., nodes which are prepared to forward packets; in the Internet, these are called routers). [3] The basic concept of link-state routing is that every node constructs a map of the connectivity to the network in the form of a graph , showing which nodes are connected ...
If there are multiple routes with the same subnet mask, the route with the lowest metric is used. If there are multiple default routes, the metric is also used to determine which to use. If there are multiple routes with the same subnet mask and metric, the system may use equal-cost multi-path routing as a forwarding strategy.
OSPF's Hello messages are used as a form of greeting, to allow a router to discover other adjacent routers on its local links and networks. The messages establish relationships between neighboring devices (called adjacencies) and communicate key parameters about how OSPF is to be used in the autonomous system or area.
It is implemented through the use of the router configuration commands ip helper-address and ip forward-protocol. ip helper-address To enable the forwarding of User Datagram Protocol (UDP) broadcasts, including BOOTP, received on an interface, use the ip helper-address command in interface configuration mode.
Because a routing metric is specific to a given routing protocol, multi-protocol routers must use some external heuristic to select between routes learned from different routing protocols. Cisco routers, for example, attribute a value known as the administrative distance to each route, where smaller administrative distances indicate routes ...
Link-state update (LSU) messages contain updated information about the state of certain links on the LSDB. They are sent in response to a link state request message, and also broadcast or multicast by routers on a regular basis. Their contents are used to update the information in the LSDBs of routers that receive them.
This is in contrast to exterior gateway protocols, primarily Border Gateway Protocol (BGP), which is used for routing between autonomous systems. [5] IS-IS is a link-state routing protocol, operating by reliably flooding link state information throughout a network of routers. Each IS-IS router independently builds a database of the network's ...