Chapter 9

1:
A:	From the perspective of an OSPF router, a neighbor is another OSPF router that is attached to one of the first router's directly connected links.
2:
A:	An OSPF adjacency is a conceptual link to a neighbor over which LSAs can be sent.
3:
A:	The five OSPF packet types, and their purposes, are: Hellos, which are used to discover neighbors, and to establish and maintain adjacencies Updates, which are used to send LSAs between neighbors Database Description packets, which a router uses to describe its link state database to a neighbor during database synchronization Link State Requests, which a router uses to request one or more LSAs from a neighbor's link state database Link State Acknowledgments, used to ensure reliable delivery of LSAs
4:
A:	A router originates a link state advertisement to describe one or more destinations. An OSPF Update packet transports LSAs from one neighbor to another. Although LSAs are flooded throughout an area or OSPF domain, Update packets never leave a data link.
5:
A:	The most common LSA types and their purposes are: Type 1 (Router LSAs) are originated by every router and describe the originating router, the router's directly connected links and their states, and the router\xd5 s neighbors. Type 2 (Network LSAs) are originated by Designated Routers on multiaccess links and describe the link and all attached neighbors. Type 3 (Network Summary LSAs) are originated by Area Border Routers and describe inter-area destinations. Type 4 LSAs (ASBR Summary LSAs) are originated by Area Border Routers to describe Autonomous System Boundary Routers outside the area. Type 5 (AS External LSAs) are originated by Autonomous System Boundary Routers to describe destinations external to the OSPF domain. Type 7 (NSSA External LSAs) are originated by Autonomous System Boundary Routers within not-so-stubby areas.
6:
A:	The link state database is where a router stores all the OSPF LSAs it knows of, including its own. Database synchronization is the process of ensuring that all routers within an area have identical link state databases.
7:
A:	The default OSPF HelloInterval is 10 seconds.
8:
A:	The default RouterDeadInterval is four times the HelloInterval.
9:
A:	A Router ID is an address by which an OSPF router identifies itself. It is either the numerically highest IP address of all the router's loopback interfaces, or if no loopback interfaces are configured, it is the numerically highest IP address of all the router's LAN interfaces.
10:
A:	An area is an OSPF sub-domain, within which all routers have an identical link state database.
11:
A:	Area 0 is the backbone area. All other areas must send their inter-area traffic through the backbone.
12:
A:	MaxAge, 1 hour , is the age at which an LSA is considered to be obsolete.
13:
A:	The four OSPF router types are: Internal Routers, whose OSPF interfaces all belong to the same area Backbone Routers, which are Internal Routers in Area 0 Area Border Routers, which have OSPF interfaces in more than one area Autonomous System Boundary Routers, which advertise external routes into the OSPF domain
14:
A:	The four OSPF path types are: Intra-area paths Inter-area paths Type 1 external paths Type 2 external paths
15:
A:	The five OSPF network types are: Point-to-point networks Broadcast networks Non-broadcast multi-access (NBMA) networks Point-to-multipoint networks Virtual links
16:
A:	A Designated Router is a router that represents a multiaccess network, and the routers connected to the network, to the rest of the OSFP domain.
17:
A:	Cisco IOS calculates the outgoing cost of an interface as 10 8 /BW, where BW is the configured bandwidth of the interface.
18:
A:	An area is partitioned if one or more of its routers cannot send a packet to the area's other routers without sending the packet out of the area.
19:
A:	A virtual link is a tunnel that extends an OSPF backbone connection through a non-backbone area.
20:
A:	A stub area is an area into which no type 5 LSAs are flooded. A totally stubby area is an area into which no type 3, 4, or 5 LSAs are flooded, with the exception of type 3 LSAs to advertise a default route. Not-so-stubby areas are areas through which external destinations are advertised into the OSPF domain, but into which no type 5 LSAs are sent by the ABR.
21:
A:	OSPF network entries are entries in the route table, describing IP destinations. OSPF router entries are entries in a separate route table that record only routes to ABRs and ASBRs.
22:
A:	Type 2 authentication uses MD5 encryption, whereas type 1 authentication uses clear-text passwords.
23:
A:	The three fields in the LSA header that distinguish different LSAs are the Type, Advertising Router, and the Link State ID fields. The three fields in the LSA header that distinguish different instances of the same LSA are the Sequence Number, Age, and Checksum fields.