“OSPF Practice Test”

In OSPF NBMA broadcast mode, the network is treated as a broadcast network even though it may not actually be a broadcast network. In this mode, OSPF routers can dynamically discover and form adjacencies with other routers on the network without the need for static neighbor configurations. This is because OSPF packets are sent to the multicast address, allowing routers to learn about each other automatically. Therefore, the statement that you do not need to define static neighbors when using OSPF NBMA broadcast mode is true.

When configuring an area to be totally stubby, the "no-summary" keyword does not have to be added to all devices that belong to the area. This keyword is used in OSPF to prevent the generation of summary routes in the area and is typically only added to the area's ABR (Area Border Router). By enabling the "no-summary" keyword on the ABR, it will advertise only the default route into the totally stubby area. Therefore, the correct answer is False.

A loopback address is configured on a router to provide a single IP address for management purposes. This address is always up and available, regardless of the status of other interfaces. Additionally, the loopback address serves as a consistent router ID, allowing for easier identification and management of the router.

ABR stands for Area Border Router and ASBR stands for Autonomous System Boundary Router. Both ABR and ASBR are OSPF device types that have the ability to summarize information. ABRs are responsible for connecting different OSPF areas and they summarize the routing information between these areas. ASBRs, on the other hand, are responsible for connecting OSPF with external routing domains and they summarize the routing information between OSPF and these external domains. Therefore, both ABRs and ASBRs have the capability to summarize information in OSPF.

The correct answer is "Router(config-if)#ip ospf network point-to-point". This command is used to change the OSPF network type for the interface serial 0/0 to point-to-point mode. The "ip ospf network point-to-point" command is specifically used to configure the OSPF network type for a specific interface.

RFC 2328 describes OSPF version 2.

The correct answer is LSA Type 3. LSA Type 3 is used to advertise network summary information to other areas in OSPF. It is generated by the Area Border Router (ABR) and contains information about networks within the area that are not directly connected to the ABR. This information is then used to build the routing table entries for inter-area routes. The "O IA" in the routing table entry indicates that the route was learned from an OSPF inter-area route.

P1R1 in the diagram maintains two Link State Databases (LSDBs). This means that P1R1 has information about the network topology and routing information from two different sources. Having multiple LSDBs allows P1R1 to have a more comprehensive view of the network and make better routing decisions.

The statement is false because the next step after creating point-to-point subinterfaces is not necessarily to set the OSPF network type to NBMA point-to-point. The appropriate OSPF network type would depend on the specific network configuration and requirements.

Router Link and Network LSAs cannot move between areas because they are local to the area in which they are originated. Router Link LSAs describe the links between routers within an area, while Network LSAs describe the networks connected to a router within an area. These LSAs are not flooded outside of their originating area and are used by routers within the same area to build their routing tables. Summary and External LSAs, on the other hand, can move between areas and are used for inter-area and external routing respectively.

External Type 2 LSAs do not increment normally in the internal network because they have a higher administrative distance and are considered less trustworthy than internal LSAs. On the other hand, External Type 1 LSAs do increment normally within the internal network because they have a lower administrative distance and are considered more trustworthy.

The given output is related to networking devices in a network. BDR stands for Backup Designated Router, which is a role assigned to a router in a network that acts as a backup to the Designated Router (DR). The DR and BDR are responsible for maintaining the network topology and exchanging routing information. Therefore, the correct answer suggests that the output represents a BDR device in the network.

The command "Ip ospf name-lookup" will allow you to see device names instead of router-ids when doing OSPF display commands. This command enables the OSPF process to resolve router-ids to their corresponding device names, providing more meaningful and easily identifiable information in the output.

The two main functions of the DR (Designated Router) are to generate LSA (Link State Advertisement) type 2 and to distribute updates on the multi-access segment. The DR is responsible for maintaining and managing the LSDB (Link State Database) for the multi-access segment. It generates LSA type 2, which contains information about the network's routers and their connections. Additionally, the DR distributes updates to other routers on the multi-access segment, ensuring that all routers have the most up-to-date information about the network topology.

An ASBR (Autonomous System Boundary Router) is not able to inject external protocol information into all areas. ASBRs are routers that connect different autonomous systems and exchange routing information between them. They are responsible for injecting external routes into the local routing domain, but this information is not automatically propagated to all areas within the domain. Instead, ASBRs typically inject external routes into a specific area or areas based on the network design and routing policies in place. Therefore, the statement that an ASBR can inject external protocol information into all areas is false.

Configuring a point-to-point subinterface on one Cisco device and a point-to-multipoint subinterface on the other device in a frame-relay network will not allow these devices to establish an adjacency. Point-to-point subinterfaces are used for direct connections between two devices, while point-to-multipoint subinterfaces are used for connections to multiple devices. Since the configurations are not compatible, the devices will not be able to establish an adjacency.

The correct answer is Router(config-if)#ip ospf hello-interval xx,Router(config-if)#ip ospf dead-interval xx. These two commands are used to adjust the hello and dead intervals on a Cisco router. The first command is used to configure the hello interval for a specific OSPF interface, while the second command is used to configure the dead interval for the same interface. By adjusting these intervals, the router can control the frequency of OSPF hello packets and the length of time before declaring a neighbor as unreachable.

In a hub-and-spoke topology with only one IP subnet, the recommended OSPF mode to use would be Point-to-Multipoint. This mode allows for efficient communication between the hub (P1R1) and multiple spokes, without the need for a full mesh of point-to-point links. It is suitable for scenarios where there is a central hub that needs to communicate with multiple remote sites.

In a point-to-multipoint network topology, OSPF demand circuit should be done on the hub device. The hub device is responsible for connecting multiple spoke devices in the network. By implementing OSPF demand circuit on the hub, it allows the hub to dynamically establish and tear down connections with the spoke devices based on demand, optimizing network resources and improving efficiency.

The correct answer is NBMA. NBMA (Non-Broadcast Multi-Access) networks require static neighbor configuration in OSPF. In NBMA networks, OSPF does not automatically discover neighbors like it does in broadcast or point-to-point networks. Instead, the network administrator needs to manually configure the neighbors in the NBMA network for OSPF to function properly.

In a hub and spoke topology with routing equipment from different vendors, using the Point-to-Multipoint OSPF mode would minimize the potential number of IP addresses used in configuring these devices. This mode allows multiple devices to communicate with each other using a single IP subnet, reducing the need for individual IP addresses for each device. This is beneficial in a multi-vendor environment where IP address allocation may be limited or complicated.

To make area 1 in the diagram a stub area, the devices P1R1, P1R2, and P1R3 would need to receive the appropriate configuration. This configuration would involve implementing the stub area feature on these devices, which would limit the number of routes advertised into the area. By configuring these devices as stub routers, they would not advertise external routes into area 1, making it a stub area.

The correct answer is "Show ip ospf database border-router." This command will display the OSPF database for the specified border router, showing all the ABR devices for the local area and all the ASBR devices in the AS.

In order for OSPF neighbors to establish adjacencies, the fields that have to match between them are the Stub Flag and Timers. The Stub Flag indicates whether a router is configured as a stub router, which affects the way it advertises routes. Timers, on the other hand, determine the intervals at which OSPF neighbors exchange hello packets and other OSPF messages. Matching these fields ensures that the OSPF neighbors have compatible configurations and can communicate effectively.

LSA type 5 packets are accepted in the Backbone and Standard areas. The Backbone area is the central area of an OSPF network and is responsible for interconnecting different areas. The Standard area is a regular area within an OSPF network. However, LSA type 5 packets are not accepted in the Stub and NSSA (Not-So-Stubby Area) areas. Stub areas do not allow external routes, while NSSA areas allow external routes but with some limitations.

The OSPF NBMA mode does not have the characteristic of being Cisco proprietary. This means that it is not exclusive to Cisco devices and can be implemented on other network devices as well. The other characteristics listed, such as having one IP subnet, full mesh topology, and static neighbor definitions, are all valid characteristics of the OSPF NBMA mode.

The default Hello and Dead timers for NBMA mode are 10 and 40 seconds respectively. For Point-to-Point mode, the default Hello and Dead timers are 30 and 120 seconds respectively.

The default External LSA type is Type 2, which means that it does not increment its cost normally as it passes from one device to another. Type 2 LSAs are used to describe the routes to networks outside of the OSPF autonomous system. Unlike Type 1 LSAs, which have a cost that increments as it passes through routers, Type 2 LSAs have a fixed cost that does not change. This allows for more predictable routing decisions and helps to maintain stability in the network.

The initial age value assigned to an LSA when sent to a neighbor is 0x00000001.

An OSPF router with only point-to-point leased lines cannot generate a "Network Link" type of LSA. This is because a "Network Link" LSA is used to advertise the presence of a multi-access network, such as an Ethernet LAN, to other routers in the OSPF area. Since point-to-point leased lines are not considered multi-access networks, the OSPF router cannot generate this type of LSA to advertise its presence.

OSPF operates in the NBMA (Non-Broadcast Multi-Access) mode by default on a point-to-multipoint subinterface. NBMA is a network type that does not support broadcast or multicast traffic, and it is commonly used in Frame Relay or ATM networks. In this mode, OSPF uses a designated router (DR) and backup designated router (BDR) to establish adjacencies with other routers on the network.

The MaxAge value determines the maximum time a router will keep a received LSA before discarding it. In this case, the MaxAge value of 60 minutes indicates that the router will keep the LSA for up to 60 minutes before considering it outdated. The LSA Refresh value determines the time interval after which a router will regenerate and flood its own LSAs. A value of 30 minutes means that the router will refresh and flood its LSAs every 30 minutes. Therefore, the given answer of MaxAge – 60 min and LSA Refresh – 30 min is appropriate.

The commands "show ip ospf neighbor" and "show ip ospf interface" can be used to determine whether a device is a DR/BDR. The "show ip ospf neighbor" command displays information about OSPF neighbors, including their roles as DR or BDR. The "show ip ospf interface" command provides information about OSPF interfaces, including the DR and BDR roles assigned to them.

The OSPF reference bandwidth is the value used to calculate the cost of a link in OSPF. The cost is inversely proportional to the bandwidth, so a higher reference bandwidth will result in a lower cost for a given link. In this case, a T3 link with a cost of 50 means that the reference bandwidth needs to be set in such a way that the resulting cost is 50. Among the given options, the reference bandwidth of 2237 would yield a cost of 50 for a T3 link.

The given IP address 172.16.2.255/16 is a valid host address. The IP address itself falls within the private IP address range (172.16.0.0 - 172.31.255.255) and the subnet mask /16 indicates that the first 16 bits of the IP address represent the network portion, leaving the remaining 16 bits for the host portion. Therefore, 172.16.2.255 is a valid host address within the network.

The given answer is correct because the "range" command is used in OSPF to summarize information for a specific area. In this case, the "range" command is used in both Area 0 and Area 1 to summarize the IP address ranges. The specified ranges, 10.0.0.0/8 in Area 0 and 192.168.1.0/24 in Area 1, will summarize the information for both areas that P1R1 attaches to.

The OSPF RFC defines two NBMA modes: Point-to-Multipoint and NBMA. Point-to-Multipoint mode allows communication between a single sender and multiple receivers, while NBMA (Non-Broadcast Multiple Access) mode is used for networks where broadcast communication is not possible. The other options, Point-to-Point and Broadcast, are not specifically defined as NBMA modes in the OSPF RFC.

The correct answer options reflect valid ways of influencing link costing in OSPF. The command "Router(config-if)#ip ospf cost 100" allows the administrator to manually set the cost of a specific interface. On the other hand, the command "Router(config-router)#auto-cost reference-bandwidth 3000" sets the reference bandwidth for calculating the cost of OSPF links based on the bandwidth of the interface. Both options provide a means to influence link costing in OSPF.

Designated Router elections occur on Ethernet networks and ATM networks running in NBMA (Non-Broadcast Multiple Access) mode. In Ethernet networks, the Designated Router is responsible for maintaining the Link State Database and flooding Link State Advertisements. In NBMA mode, ATM networks use virtual circuits to connect multiple endpoints, and the Designated Router is elected to optimize the flooding of Link State Advertisements in this type of network.

The route 172.16.1.0/25 with OSPF/10 and metric 28 will be used for traffic destined for 172.16.1.1. This is because the more specific route (172.16.1.0/25) will be preferred over the less specific route (172.16.1.0/24). Additionally, within the same prefix length, the route with the lower metric value (in this case, 28) will be preferred over the route with the higher metric value (metric 23).

The "Show ip ospf database router" command is used to view the detailed router link entries in the Link State Database (LSDB) for OSPF. This command specifically displays information related to OSPF routers in the database. By using this command, network administrators can get a comprehensive view of the OSPF routers and their link information within the network.

The initial sequence number used for all LSAs is 0x80000000.

In OSPF, each router forms an adjacency with every directly connected router. In this scenario, there are 8 routers connected via an Ethernet switch. Each router will form an adjacency with the other 7 routers, resulting in a total of 56 adjacencies. However, since OSPF uses a two-way handshake, the number of adjacencies is divided by 2, resulting in 28 adjacencies. However, the question specifically asks for the number of adjacencies in a full state. In a full state, each adjacency goes through multiple states (such as Down, Attempt, Init, 2-Way, Exstart, Exchange, Loading, Full) before reaching the Full state. Since there are 8 routers and each adjacency goes through these states, there will be a total of 8 * 7 = 56 states. However, each adjacency is counted twice (once for each router involved), so the total number of adjacencies in a full state is 56 / 2 = 28. 

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In a full mesh frame-relay topology, the easiest and most appropriate configuration would be to use the "Broadcast" configuration. This configuration allows for efficient communication between multiple devices in the network by allowing one device to send a message to all other devices simultaneously. This is particularly useful in a full mesh topology where every device is directly connected to every other device. Using the "Broadcast" configuration ensures that all devices receive the message, simplifying communication and reducing the need for complex routing protocols.

The question asks about the number of LSA type 3 entries maintained by P1R1 in the diagram. However, the answer options provided do not include the correct number of entries. Therefore, none of the answer options accurately represent the correct answer.

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The correct answer is Point-to-Multipoint. OSPF NBMA (Non-Broadcast Multi-Access) is a network type used in OSPF routing protocol for non-broadcast networks. Cisco proprietary modes are specific to Cisco devices and not supported by other vendors. Point-to-Multipoint is a valid OSPF NBMA mode, but it is not a Cisco proprietary mode.

The correct answer is NBMA, 30 & 120s. When the encapsulation frame-relay command is typed on serial 0/0, the default OSPF mode for this interface is NBMA. The default hello timer is 30 seconds and the default dead timer is 120 seconds.

Multicast: OSPF uses multicast addresses (224.0.0.5 for all OSPF routers, and 224.0.0.6 for all designated routers) to send OSPF packets to all routers in the network segment.

Unicast: OSPF also uses unicast addresses to send OSPF packets directly to specific routers.

Broadcast and Anycast addresses are not used as destinations for OSPF.

Static neighbors would be required on an NBMA (Non-Broadcast Multi-Access) network type and on a Point-to-Multipoint Non-Broadcast network type. In both of these network types, there is no automatic neighbor discovery or broadcast capability, so static neighbors need to be manually configured in order for the devices to communicate with each other.

The first statement is true because the backbone can be used as a transit area in a virtual link configuration. This means that traffic can pass through the backbone area to reach other areas in the network.

The second statement is also true because the configuration syntax in virtual link configuration references the router-id of the remote devices. This is necessary to establish the virtual link and ensure proper connectivity between the devices.

The third statement is false because stub areas cannot act as transit areas. Stub areas are designed to have only one exit point, which is the ABR (Area Border Router) connecting it to the backbone area.

The fourth statement is also false because the configuration for virtual link needs to be done on both ABRs (Area Border Routers) at each end of the virtual link. It is not sufficient to configure it on just one ABR.

The Point-to-Multipoint network type allows for communication between a single hub device and multiple spoke devices. The NBMA (Non-Broadcast Multi-Access) network type is used in situations where a broadcast cannot be sent, such as in a Frame Relay network. Both of these network types are suitable for scenarios where devices from different vendors are used. The Broadcast network type is not suitable as it assumes all devices are from the same vendor and can send and receive broadcast messages. The Point-to-Point network type is also not suitable as it only allows for communication between two devices.

To configure Point-to-Multipoint mode in OSPF, the "ip ospf network" command needs to be used. This command specifies the type of network being used. Additionally, the "network x.x.x.x area x" command is also required to define the network address and the corresponding OSPF area. These commands together enable the router to establish OSPF adjacency and exchange routing information in Point-to-Multipoint mode. The other options, "neighbor" and "ip ospf priority," are not specifically related to configuring Point-to-Multipoint mode.

OSPF represents a numbered point-to-point link in the LSDB as either a Stub Link or a Point-to-point link. A Stub Link is a link that connects a router to a network, but does not have any other routers connected to it. A Point-to-point link, on the other hand, is a direct link between two routers. Both of these representations are used in OSPF to accurately depict the topology of the network in the LSDB.

LSA Type 1 (Router LSA): Generated by every router and includes information about the router itself and its directly connected links. These LSAs do not cross area boundaries.

LSA Type 2 (Network LSA): Generated by the Designated Router (DR) on multi-access networks, providing information about all routers on that network segment.

LSA Type 3 (Summary LSA): Generated by Area Border Routers (ABRs) to advertise networks from one area to another. This type of LSA allows routers in one area to learn about networks in different areas.

LSA Type 4 (ASBR Summary LSA): Generated by ABRs to inform routers about the presence of an ASBR (Autonomous System Boundary Router) in another area.

LSA Type 5 (External LSA): Used to advertise external routes (routes to networks outside the OSPF autonomous system) that are injected into OSPF by an ASBR.

Therefore, LSA Type 3 is the correct answer.

Based on the diagram and the assumption that all 3 devices are from different vendors, both the Stub and Not so stubby (NSSA) variations of stub areas can be configured. The Stub area is a type of OSPF area that allows only summary routes to be advertised into the area, while the Not so stubby (NSSA) area is similar to the Stub area but allows the importation of external routes with the use of an Autonomous System Boundary Router (ASBR). Therefore, both of these variations can be configured in this scenario.

OSPF (Open Shortest Path First) is a dynamic routing protocol that allows the redistribution of various types of routes into its routing table. Static routes can be redistributed into OSPF to provide alternative paths for network traffic. Connected interfaces, which are directly connected to the OSPF router, can also be redistributed to allow OSPF to advertise these networks to other routers. BGP (Border Gateway Protocol), another dynamic routing protocol, can be redistributed into OSPF to exchange routing information between different autonomous systems. Lastly, OSPF can redistribute its own routes to ensure that all OSPF routers have the same routing information.

In a single area OSPF design, there are several types of Link State Advertisements (LSAs) that might exist. These include Router links, which are used to advertise the links of the router itself within the area. Network links are used to advertise the links of the networks connected to the router within the area. External links are used to advertise routes from other routing domains or autonomous systems. Therefore, in a single area OSPF design, the LSAs that might exist are Router links, Network links, and External links.

To configure MD5 authenticated OSPF updates, the following commands would be required:

1. Router(config-router)#area x authentication message-digest: This command enables MD5 authentication for OSPF updates in a specific OSPF area.

2. Router(config-if)#ip ospf authentication message-digest: This command enables MD5 authentication for OSPF updates on a specific interface.

3. Router(config-if)#ip ospf message-digest-key 1 md5 cisco: This command configures a message-digest key with ID 1 and the MD5 algorithm, using the password "cisco" for OSPF authentication.

These commands ensure that OSPF updates are authenticated using MD5 encryption for security purposes.

In NBMA point-to-point mode with point-to-point subinterfaces, the "Neighbor" command would typically not be used because in this mode, each subinterface is treated as a separate point-to-point link and does not require neighbor statements. The "Ip ospf network" command would also not be used as it is used to specify the OSPF network type, which is not applicable in this mode. Therefore, "All of the above" is the correct answer as both "Neighbor" and "Ip ospf network" commands would typically not be used in this scenario.

If the network is using NBMA (Non-Broadcast Multi-Access) mode, the OSPF (Open Shortest Path First) routing protocol needs to be configured accordingly. The "ip ospf network" command is used to specify the type of network, and in this case, it would be used to set the network type to NBMA. The "ip ospf priority" command is used to set the priority for the OSPF router in the network. The "network x.x.x.x area x" command is used to advertise the network with the specified IP address and assign it to the specified OSPF area.

Based on the OSPF lab diagram provided, the correct commands to configure PXR1 (which functions as an Area Border Router or ABR, connecting Area 0.0.0.0 and Area 1.0.0.0) are as follows:

Router(config-router)#network 10.1.1.0 0.0.0.255 area 0

This command correctly assigns the network 10.1.1.0/24 to Area 0.

Router(config-router)#network 192.168.1.0 0.0.0.255 area 1

This command correctly assigns the network 192.168.1.0/24 to Area 1.

These commands reflect the valid OSPF configuration necessary to set up PXR1 as an ABR, enabling it to route traffic between Area 0 and Area 1.

The correct order of the OSPF adjacency states is as follows: Initial, Two way, Exstart, Exchange, Loading, Full. In the Initial state, OSPF routers are initialized and ready to begin forming adjacencies. The Two way state is when routers have exchanged hello packets and have confirmed bidirectional communication. The Exstart state is where routers negotiate the master/slave relationship. The Exchange state is when routers exchange link-state database information. The Loading state is when routers request and receive missing link-state information. Finally, the Full state is when routers have a complete and synchronized link-state database.