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Questions and Answers
What protocol is used to exchange routing information among routers?
What protocol is used to exchange routing information among routers?
- BGP
- OSPF (correct)
- EIGRP
- RIP
Which OSPF packet is primarily used to discover neighboring routers?
Which OSPF packet is primarily used to discover neighboring routers?
- Link-state update packet
- Database description packet
- Link-state acknowledgment packet
- Hello packet (correct)
What does the link-state database (LSDB) represent in OSPF?
What does the link-state database (LSDB) represent in OSPF?
- Information about all routers within an area (correct)
- Network performance statistics
- The list of directly connected hosts
- Topology of the physical network
What algorithm does OSPF use to calculate the shortest path to a destination?
What algorithm does OSPF use to calculate the shortest path to a destination?
What command is used to view the link-state database in OSPF?
What command is used to view the link-state database in OSPF?
What type of database contains routing information unique to each router in OSPF?
What type of database contains routing information unique to each router in OSPF?
How does OSPF determine the best routes to include in the forwarding database?
How does OSPF determine the best routes to include in the forwarding database?
What is the role of the link-state acknowledgment packet in OSPF?
What is the role of the link-state acknowledgment packet in OSPF?
What is the formula for calculating the OSPF cost?
What is the formula for calculating the OSPF cost?
What is the default reference bandwidth for OSPF?
What is the default reference bandwidth for OSPF?
What command is used to change the reference bandwidth in OSPF?
What command is used to change the reference bandwidth in OSPF?
Why might FastEthernet, Gigabit Ethernet, and 10 GigE interfaces share the same OSPF cost value?
Why might FastEthernet, Gigabit Ethernet, and 10 GigE interfaces share the same OSPF cost value?
What effect does changing the reference bandwidth have on the OSPF calculation?
What effect does changing the reference bandwidth have on the OSPF calculation?
What happens when the calculated OSPF cost is a non-integer value?
What happens when the calculated OSPF cost is a non-integer value?
To ensure OSPF uses the correct metric for path determination for links faster than 100 Mbps, what adjustment is necessary?
To ensure OSPF uses the correct metric for path determination for links faster than 100 Mbps, what adjustment is necessary?
What command must be configured on every router in the OSPF domain to apply changes to the reference bandwidth?
What command must be configured on every router in the OSPF domain to apply changes to the reference bandwidth?
What is the best practice when configuring static routes for a connection to the Internet?
What is the best practice when configuring static routes for a connection to the Internet?
Which command verifies the default route settings on a router?
Which command verifies the default route settings on a router?
What does the 'O*E2' designation indicate when viewing the routing table?
What does the 'O*E2' designation indicate when viewing the routing table?
What is a potential impact of a default route without a gateway on non-point-to-point interfaces?
What is a potential impact of a default route without a gateway on non-point-to-point interfaces?
What command is used to start the OSPF process on a router?
What command is used to start the OSPF process on a router?
In the context of OSPFv2, what does the 'Gateway of last resort' signify?
In the context of OSPFv2, what does the 'Gateway of last resort' signify?
What is represented by the asterisk (*) in the routing table output?
What is represented by the asterisk (*) in the routing table output?
Which of the following commands is used to configure the default information to be originated in OSPF?
Which of the following commands is used to configure the default information to be originated in OSPF?
What command provides a detailed list of settings for every OSPFv2-enabled interface?
What command provides a detailed list of settings for every OSPFv2-enabled interface?
What information does the 'show ip ospf interface' command NOT display?
What information does the 'show ip ospf interface' command NOT display?
In the output of 'show ip ospf interface brief', what is the significance of the 'Nbrs F/C' column?
In the output of 'show ip ospf interface brief', what is the significance of the 'Nbrs F/C' column?
Which type of network is indicated for the interface 'GigabitEthernet0/0/0' in the provided example?
Which type of network is indicated for the interface 'GigabitEthernet0/0/0' in the provided example?
What is the cost assigned to the link of 'GigabitEthernet0/0/1' according to the brief output?
What is the cost assigned to the link of 'GigabitEthernet0/0/1' according to the brief output?
How many adjacent neighbors are reported for 'GigabitEthernet0/0/0'?
How many adjacent neighbors are reported for 'GigabitEthernet0/0/0'?
What command would you use to get a quick summary of OSPFv2-enabled interfaces?
What command would you use to get a quick summary of OSPFv2-enabled interfaces?
Which of the following is true about the router ID in the output of the 'show ip ospf interface' command?
Which of the following is true about the router ID in the output of the 'show ip ospf interface' command?
What is the maximum number that can be assigned as a process ID for OSPF?
What is the maximum number that can be assigned as a process ID for OSPF?
How does an OSPF router primarily determine its router ID?
How does an OSPF router primarily determine its router ID?
What is the purpose of the OSPF router ID?
What is the purpose of the OSPF router ID?
Which command enables OSPF on a router?
Which command enables OSPF on a router?
What criteria does OSPF use to select the router ID if no explicit configuration is provided?
What criteria does OSPF use to select the router ID if no explicit configuration is provided?
Which command is used to configure the OSPF network for a router?
Which command is used to configure the OSPF network for a router?
What is one of the first tasks to be completed in implementing OSPFv2 in a network?
What is one of the first tasks to be completed in implementing OSPFv2 in a network?
Which of the following describes a broadcast multiaccess network in OSPF?
Which of the following describes a broadcast multiaccess network in OSPF?
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Study Notes
OSPF Packets
- Routers running OSPF exchange routing information using five types of packets: Hello, Database description, Link-state request, Link-state update, and Link-state acknowledgment packets.
- These packets discover neighboring routers and share routing information to build an accurate network map.
OSPF Databases
- OSPF messages maintain three databases: Adjacency, Link-state, and Forwarding.
- The Adjacency database lists all neighboring routers with bi-directional communication, and it's unique to each router.
- The Link-state database, or LSDB, contains information about all routers within the network. All routers in an area have an identical LSDB.
- The Forwarding database lists routes generated by an algorithm based on the LSDB and determines how to send packets to other routers.
Shortest Path First Algorithm
- The Shortest Path First (SPF) algorithm is used to build the topology database.
- The SPF algorithm calculates the shortest path to each destination using a cumulative cost metric.
- The SPF algorithm creates an SPF tree with each router at the root and calculates the shortest path to each node.
- This tree is used to calculate the best routes, which are then placed into the forwarding database and used to create the router's routing table.
OSPF Cost Calculation
- The OSPF cost is calculated using the formula: Cost = reference bandwidth / interface bandwidth.
- The default reference bandwidth is 100,000,000 bps.
- The cost value must be an integer.
Adjusting the OSPF Cost
- FastEthernet, Gigabit Ethernet, and 10 GigE interfaces share the same cost due to the OSPF cost being an integer.
- To address this, you can either adjust the reference bandwidth using the auto-cost reference-bandwidth command on each OSPF router or manually set the OSPF cost using the ip ospf cost command on necessary interfaces.
Default Route Propagation
- OSPF supports the propagation of a default route using the default-information originate command in router configuration mode.
- The default route is configured and propagated to all other OSPF routers in the routing domain.
OSPFv2 Configuration
- OSPFv2 is enabled using the router ospf process-id global configuration mode command.
- The process-id is a number between 1 and 65,535.
OSPF Router ID
- The OSPF router ID is a 32-bit value, represented as an IPv4 address.
- It's used by routers to synchronize OSPF databases and participate in the election of designated routers (DR and BDR).
- Routers choose the router ID based on these criteria in order of priority:
- Explicitly configured using the OSPF router-id command.
- The highest IPv4 address of any configured Loopback interface.
- The highest active IPv4 address of any physical interface.
OSPF Network Configuration
- The network command configures an OSPF network.
- The basic syntax is network network-address wildcard-mask area area-id.
- Any interface that matches the network-address can send and receive OSPF packets.
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