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29 Cards in this Set
- Front
- Back
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Link State Database |
The data structure held by an OSPF router for the purpose of storing topology data.
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Shortest Path First (SPF)
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The name of the algorithm OSPF uses to analyze the LSDB. The analysis determines the best (lowest cost) route for each prefix/length.
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Link State Update (LSU)
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The name of the OSPF packet that holds the detailed topology information, specifically LSAs.
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Link State Advertisement (LSA)
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The name of a class of OSPF data structures that hold topology information. LSAs are held in memory in the LSDB and communicated over the network in LSU messages.
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Area
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A contiguous grouping of routers and router interfaces. Routers in an area strive to learn all topology information about the are, but they do not learn topology information about areas to which they do not connect.
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Area Border Router (ABR)
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A router that has interfaces connected to at least two different OSPF areas, including the backbone area. ABRs hold topology data for each area, and calculate routes for each area, and advertise about those routes between areas.
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Backbone router
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Any router that has at least one interface connected to the backbone area.
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Internal routers
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A router that has interfaces connected to only one area, making the router completely internal to that one area.
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Designated Router (DR)
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On multiaccess data links like LANs, an OSPF router elected by the routers on that data link to perform special functions. These functions include the generation of LSAs representing the subnet, and playing a key role in the database exchange process.
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Backup Designated Router (BDR)
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A router on a multiaccess data link that monitors the DR and becomes prepared to take over for the DR, should the DR fail.
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What does OSPF use as a router ID?
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When OSPF process is initialized, as follows, in the listed order of precedence:
1 - Use the router ID defined in the router-id x.x.x.x OSPF router subcommand. 2 - Use the highest IP address of any up/up loopback interface. 3 - Use the highest IP address of any up/up non-loopback interface. |
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show ip ospf interface brief
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Lists the interfaces on which OSPF is enabled (based on the 'network' commands); it omits passive interfaces.
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show ip protocols
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Lists the contents of the 'network' configuration commands for each routing process, and a list of enabled but passive interfaces.
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show ip ospf neighbors
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Lists known neighbors, including neighbor state; does not list neighbors for which some mismatched parameter is preventing a valid OSPF neighbor relationship.
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show ip ospf database
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Lists all LSAs for all connected areas.
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show ip route
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Lists the contents of the IP routing table, listing OSPF-learned routes with a code of 'O' on the left side of the output.
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Transport
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IP, protocol type 89 (does not use UPD or TCP).
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Metric
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Based on cumulative cost of all outgoing interfaces in a route. The interface cost defaults to a function of interface bandwidth but can be set explicitly.
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Hello Interval
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Interval at which a router send OSPF Hello messages on an interface.
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Dead interval
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Timer used to determine when a neighboring router has failed, based on a router not receiving any OSPF messages, including Hellos, in this timer period.
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Update destination address
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Normally sent to 224.0.0.5 (All SPF Routers) and 225.0.0.6 (All Designated Routers).
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Full or partial updates
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Full updates are used when new neighbors are discovered; otherwise, partial updates are used.
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Authentication
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Supports MD5 and clear-text authentication.
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VLSM/classless
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OSPF includes the mask with each route, also allowing it to support discontiguous networks and VLSM.
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Route Tags
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Allows OSPF to tag routes as they are redistributed into OSPF.
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Next-hop field
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Supports the advertisement of routes with a different next-hop router than the advertising router.
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Manual route summarization
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Allows route summarization at ABR routers only.
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Items in a Hello Packet
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OSPF Router ID, Stub area flag, Hello interval, Dead interval, subnet mask, list of neighbors reachable on the interface, area ID, router priority, DR IP address, BDR IP address, authentication digest
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Must meet to become neighbors
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Interface IP address must be in same subnet, must not be a passive interface, must be in same area, Hello and Dead timer must match, Unique router IDs, MTU must match, authentication if configured
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