Action: Recalculate the attached network’s Backup Designated Router and Designated Router, as shown in Section 9.4. As a result of this calculation, the new state of the interface will be either DR Other, Backup or DR. State(s): Any State Event: InterfaceDown New state: Down Action: All interface variables are reset, and interface timers disabled. In this case, in an attempt to discover the attached network’s Designated Router the interface state is set to Waiting and the single shot Wait Timer is started. OSPF supports the following types of physical networks: Point-to-point networks A network that joins a single pair of routers. Index value. For the other link types it specifies the router’s associated IP interface address. They are defined in Appendix C. The name of each architectural constant follows, together with its value and a short description of its function. The value of MaxAge is set to 1 hour. Status Set to either Advertise or DoNotAdvertise. Point-to-point physical networks are an exception – they are considered a single network no matter how many (if any at all) IP network/subnet numbers are assigned to them. This article has been created by GSA Co nten t Generator DEMO.
Networks forms the protocol’s topological database. This externally derived data is kept separate from the OSPF protocol’s link state data. To see why it is necessary to advertise the location of each ASBR, consult Section 16.4.) Other than the difference in the Link State ID field, the format of Type 3 and 4 link state advertisements is identical. The collected link state advertisements of all routers. For example, the inoperative state is listed first, followed by a list of intermediate states before the final, fully functional state is achieved. Discard all routers from the list that are ineligible to become Designated Router. The Designated Router is elected by the Hello Protocol. For example, the ExternalRoutingCapability (below called the E-bit) has meaning only in OSPF Hello Packets. 1.2. Definitions of commonly used terms This section provides definitions for terms that have a specific meaning to the OSPF protocol and that are used throughout the text. This conte nt has be en creat ed by GSA C ontent Gener ator D emoversion.
This section gives a brief description of the developments in link-state technology that have influenced the OSPF protocol. 1.3. Brief history of link-state routing technology OSPF is a link state routing protocol. Abbreviated as AS. Interior Gateway Protocol The routing protocol spoken by the routers belonging to an Autonomous system. Autonomous System A group of routers exchanging routing information via a common routing protocol. Neighboring routers Two routers that have interfaces to a common network. The receive processing of OSPF packets is detailed in Section 8.2. The sending of OSPF packets is explained in Section 8.1. A.3.1 The OSPF packet header Every OSPF packet starts with a common 24 byte header. Router ID A 32-bit number assigned to each router running the OSPF protocol. This number uniquely identifies the router within an Autonomous System. Externally derived routing data (e.g., routes learned from the Exterior Gateway Protocol (EGP)) is passed transparently throughout the Autonomous System. This data has be en gener ated by GSA Content Gene rator DEMO !
First, if used effectively, it can greatly
reduce the administrative overhead of the routing configura-
tion in the internetwork by reducing the number of route
entries that need to be kept accurate. The Designated Router concept enables a reduction in the number of adjacencies required on a multi-access network. Maintain neighbor relationships. On multi-access networks the Hello Protocol can also dynamically discover neighboring routers. Figure 4 shows graphically the link state representation of the two kinds of transit vertices: routers and multi-access networks. The neighbor events are documented in Section 10.2. The graph in Figure 12 shows the state changes effected by the Hello Protocol. This is regardless of such an interface’s state. This includes the state of the router’s interfaces and adjacencies. The flooding algorithm is reliable, ensuring that all routers have the same collection of link state advertisements. An interface has state information associated with it, which is obtained from the underlying lower level protocols and the routing protocol itself. If there is no routing table entry for the network (the usual case), a routing table entry for the IP network should be added.