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NETW204 Ch 11
OSPF
| Question | Answer |
|---|---|
| Autonomous System Boundary Router (ASBR) | The OSPF router located between an OSPF autonomous system network and a non-OSPF network. ASBRs run both OSPF and another routing protocol, such as RIP. ASBRs must reside in a non-stub OSPF area. |
| Backup Designated Router (BDR) | A router that becomes the designated router if the current designated router fails. The BDR is the OSPF router with the second-highest priority at the time of the last DR election. |
| Database Description (DBD) | A packet used in OSPF that contains link-state advertisement (LSA) headers only and describes the contents of the entire link-state database. Routers exchange DBDs during the exchange phase of adjacency creation. |
| Designated Router (DR) | OSPF router that generates LSAs for a multiaccess network and has other special responsibilities in running OSPF. Each multiaccess OSPF network that has at least two attached routers has a designated router that is elected by the OSPF Hello protocol. |
| DROther | Routers that are not DR or BDR. They are the other routers in the OSPF network. |
| Flapping Link | Routing problem where an advertised route between two nodes alternates (flaps) back and forth between two paths because of a network problem that causes intermittent interface failures. |
| Link-state Acknowledgment (LSAck) | Acknowledges receipt of LSA packets. Link-state acknowledgment packets are Type 5 OSPF packets. |
| Link-state Advertisements (LSA) | Broadcast packet used by link-state protocols that contains information about neighbors and path costs. LSAs are used by the receiving routers to maintain their routing tables. |
| Link-state Request (LSR) | Link-state request packets are Type 3 OSPF packets. The link-state request packet is used to request the pieces of the neighbor's database that are more up to date. |
| Link-state Update (LSU) | Link-state update packets are Type 4 OSPF packets. A link-state update packet carries a collection of link-state advertisements one home father from its origin. |
| Multiaccess Networks | Networks that allow multiple devices to connect and communicate simultaneously. |
| Nonbroadcast Multiaccess (NBMA) | Term describing a multiaccess network that either does not support broadcasting (such as X.25) or in which broadcasting is not feasible (for example, an SMDS broadcast group or an extended Ethernet that is too large). |
| OSPF Area | A logical set of network segments (CLNS-, DECnet-, or OSPF-based) and their attached devices. Areas are usually connected to other areas through routers, making up a single autonomous system. |
| SPF Schedule Delay | After executing the show ip ospf command, you will see the parameter "SPF schedule delay X seconds". This is the delay time of SPF calculations. |
| Give three statements regarding routing protocols that use the link-state algorithm. | They are known collectively as link-state routing protocols, They maintain a database of the network topology, & They are based on the Dijkstra algorithm. |
| Creates & maintains neighbor adjacencies | Hello Packet |
| Triggered when a topology change has occurred | LSA - Link-state Advertisements |
| Description of an interface and its relationship to other routers | State of the link |
| Calculates the best path to each destination network | SPF algorithm |
| What reasons would a network administrator have for using loopback interfaces when configuring OSPF? Give two reasons. | Loopbacks are logical interfaces and do not go down & The loopback address will be used as the router ID, overriding the physical IP address values. |
| In what types of networks will OSPF designated routers no be elected? Give 2 types. | Point-to-Point (PTP) & Point-to-Multipoint |
| A network administrator enters the router ospf 100 command. What is the function of the number 100 in this command? | Process ID |
| On a router running OSPF, what is the purpose of entering the bandwidth 56 command on a serial interface? | Changes the cost value. |
| What factor does the Cisco implementation of OSPF use to pick the best route? | Bandwidth |
| Which command allows a router to advertise default static routes via OSPF? | default-information originate |
| During an OSPF DR/BDR election, what is used to determine the DR or the BDR when participating OSPF routers have identical interface priorities? | The router ID |
| Which packet type is invalid for OSPF? Hello, LRU, LSR, LSAck, or DBD | LRU |
| In the router ospf command, does the process ID need to match on all routers? | No, unlike EIGRP, the OSPF is locally significant and does not need to match other OSPF routers. |
| What command enables you to verify or determine the bandwidth value of an interface used by the OSPF metric? | show interface |
| What command enables you to modify the OSPF cost of an interface without modifying the bandwidth value of that interface? | The ip ospf cost interface command. |
| What is the default Hello interval on Ethernet networks and serial point-to-point networks? What is the default Hello interval on NBMA networks? | By default, OSPF Hello packets are sent every 10 seconds on multiaccess & PTP segments & every 30 seconds on NBMA segments. |
| What values must match before two routers will form an OSPF adjacency? | Hello interval, Dead interval, Network type, & Subnet masks |
| What problems does electing a DR and BDR solve? | Creation of multiple adjacencies, one adjacency for every pair of routers. Extensive flooding of LSAs (link-state advertisements) |
| How are the DR and BDR elected? | DR is the router with the highest OSPF interface priority, and the BDR has the second highest OSPF interface priority. If the OSPF interface priorities are equal, the highest router ID is used to break the tie. |
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AZ4ME
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