CCNP ENCOR v8 Chapters 8 – 10: OSPF Test Online

Hint

LSR packets are used by OSPF routers to request link-state database information from a neighbor.

Hint

OSPF is designed with a hierarchical architecture using the concept of areas. An area is a collection of connected networks and is identified with the network command. Area 0 is a special area known as the backbone. All other areas must connect to Area 0.

Hint

The OSPFv2 process ID does not have to be the same on each router, and it is enabled globally, not separately on each interface. OSPFv3 (IPv6) uses link-local addresses to form an adjacency with a neighbor router, and requires the OSPF process to be enabled on the interface.

Hint

There is no autonomous system number to configure on OSPF. The area number is located at the end of the network statement. The cost of a link can be modified in the interface configuration mode. The process ID is local to the router.

Hint

When OSPF is operational and converged, a full adjacency is formed between routers.

Hint

A DR and BDR are elected on multiaccess networks to reduce the number of OSPF adjacencies formed. Non-DR routers will form adjacencies with the DR and BDR and send LSU packets to the AllDR-Routers multicast address of 224.0.0.6

Hint

The network 192.168.4.0 0.0.3.255 area 0 command has the correct network and wildcard mask combination to capture the four networks and activate the associated interfaces for area 0.

Hint

To get an OSPF router to advertise a default route even if there is no default route in the RIB, use the default-information originate command with the always key word.

Hint

Several variables must match for an OSPF neighbor adjacency to be formed between two OSPF routers. These variables include: area ID, hello and dead timers, interface MTU, and interface subnet.

Hint

As OSPF areas grow in size, the size of the LSDB grows and the number of type 1 and type 2 LSAs increases. Breaking an OSPF domain into multiple areas reduces the size of the LSDB and the number type 1 and 2 LSAs in each area.

Hint

OSPF uses link-state advertisement messages (LSAs) to build the LSDB and maintain routing tables. OSPF routers use LSA types 1 to 5 to describe the networks to which they are directly connected or networks which they learned from other routers. These networks can be located in other areas or can also be from non-OSPF networks. Some LSAs are used to identify an ASBR. Although most LSAs will be flooded across multiple areas, some LSAs are flooded only within the area where they originated.

Hint

When OSPF summary routes are being configured, the metric of the summary route is equal to the lowest cost network within the summary address range. The area 51 range 172.0.0.0 255.0.0.0 command identifies area 51 as the area that contains the range of networks, 172.0.0.0. through 172.255.255.254 to be summarized.

Hint

A prefix list configured on an ABR can be used to filter routes as advertised into or out of an area.

Hint

Type 1, router link, LSAs are advertised by all OSPF routers.

Hint

In a routing table, the designation O IA means the entry was learned from an interarea LSA that was generated from an ABR. The C label indicates a network that is directly connected to an interface on the router. The O label indicates a network that is advertised by another router in the same area. The label O*E2 indicates an external network. In this case, the network designation of 0.0.0.0/0 indicates that this external network is the default route for all traffic that is destined for external networks.

Hint

If not updated with a new LSA, LSAs in the local LSDB will age out at 3600 seconds and be purged from the LSDB.

Hint

When an ABR receives a type 1 LSA, it creates a type 3 LSA that references the network in the original type 1 LSA and then advertises that type 3 LSA into other areas.

Hint

Type 2 LSAs are flooded by the DR to inform other OSPF routers about multiaccess networks within an area.

Hint

An OSPF area contains one set of link-state information, although each router within the area will process that information individually to form its own SPF tree. OSPF process IDs are locally significant and are created by the administrator. Router IDs uniquely identify each router.

Hint

Because all OSPF networks start with area 0, the new area would need to be anything but area 0, The correct option would be area 15 range 172.16.8.0 255.255.248.0 because this is the correct summarization of the networks in the new area 15. The summarization must come from area 15 to area 0, because all OSPF areas interconnect via area 0. The matching bits for the correct option, in binary, are:

• 172.16.8.0 10101100.00010000.00001 000.00000000
• 172.16.10.0 10101100.00010000.00001 010.00000000
• 172.16.12.0 10101100.00010000.00001 100.00000000

Hint

Because OSPFv3 routers form neighbor adjacencies by using the link-local address of the interface, they are not required to have global addresses configured on the interfaces. Even if they do have global addresses configured, the addresses do not have to be in the same subnet on each end of the link.

Hint

Two new LSA types are added to OSPFv3, type 8, link-local LSA, and type 9, interarea prefix LSA. These two LSAs advertise unicast prefixes and prevent the need for OSPF calculations when interface addresses are added or changed.

Hint

Before the OSPFv3 process will start, IPv6 routing must be enabled with the ipv6 unicast-routing command.

Hint

OSPFv3 Hello packets for discovering neighbors are sent to the all OSPFv3 router address FF02::5.

Hint

OSPFv2 has built in support for neighbor authentication which OSPFv3 does not. OSPFv3 relies on IPsec for neighbor authentication.

Hint

OSPFv3 uses the code O to identify intrarea routes learned from type 1 LSAs in the routing table.

Hint

The basic command to implement OSPFv3 on a router uses the same process-id parameter as OSPFv2 to assign a locally-significant number to the OSPF process. OSPF does not use autonomous system numbers. Following the assignment of the process ID, a prompt will direct the user to manually assign a router ID. After the router ID is assigned, the reference bandwidth can be set.

Hint

Two new LSA types are added to OSPFv3, type 8, link-local LSA, and type 9, interarea prefix LSA. These two LSAs advertise unicast prefixes and prevent the need for OSPF calculations when interface addresses are added or changed.

Hint

Router R2 is a DR. Other OSPFv3 routers form an adjacency with the DR and send link-state updates to the ALLDRouters multicast ff02:06 and to the link -local address of the DR, which for g0/1 on R2 is fe80::2.

Hint

A network LSA (type 2) is generated by a DR to identify the routers attached to the network segment.

Hint

Interarea summarization reduces the number of type 3 LSAs advertised by an ABR.

Hint

Each OSPF router maintains a link state database (LSDB) for each area it participates in.

Hint

All OSPFv3 messages are sourced from the link-local IPv6 address of an interface. Link local addresses use the prefix FE80::/10.

Hint

OSPFv3 uses type 5, AS external LSAs, to announce default routes and routers learned through redistribution from other routing protocols.