Ch.19 Understanding OSPF Concepts

Question 1

Define Routing protocol

Answer 1

A set of messages, rules, and algorithms used by routers for the overall purpose of learning routes

Question 2

Define Routed protocol/routable protocol

Answer 2

Both terms refer to a protocol that defines a packet structure and logical addressing, allowing routers to forward or route the packets

Question 3

What is a Link-state advertisement

Answer 3

In OSPF, the name of the data structure that resides inside the LSDB and describes in detail the various components in a network, including routers and links (subnets)

Question 4

How do Link-state protocols build IP routes

Answer 4

1. The routers together build a lot pf information about the network
2. The routers flood the information, so all routers know the same info
3. Each router can calculate routes to all subnets, but from each routers own perspective

Question 5

What is a Link-state Database (LSDB)

Answer 5

A data structure with some specific information about the network topology, a collection of LSAs

Question 6

Describe the Shortest Path First algorithm

Answer 6

Analyzes the LSDB and builds the routes that the local router should add to the IP routing tables

Question 7

What command do you use to see if two routers have become OSPF neighbors

Answer 7

show ip ospf neighbor

Question 8

Describe router ID (RID)

Answer 8

32 bit numbers, which servers as each routers unique name or identifier for OSPF

Question 9

What does it mean for both routers to have reached a two way state with each other

Answer 9

It means both routers meet all OSPF configuration requirements to become neighbors and they are ready to exchange theri LSDB with each other

Question 10

What are the messages that send LSA between neighbors are called

Answer 10

Link-State Update packets (LSU)

Question 11

What does it mean when two ospf neighboring routers have reached the full state

Answer 11

They have fully exchanged the contents of their LSDBs

Question 12

What is the Hello Interval

Answer 12

With OSPF and EIGRP, an interface timer that dictates how often the router should sned Hello messages

Question 13

What is the Dead Interval

Answer 13

In OSPF, a timer used for each neighbor. A router considers the neighbor to have failed if no Hellos are received from that neighbor in the time defined by the timer

Question 14

What is a designated router

Answer 14

A router responsible for managing a streamlined process for exchanging OSPF topology information between all routers attached to that network

Question 15

What is the multicast IP address for OSPF

Answer 15

224.0.0.5

Question 16

What are the three problems with a single area design

Answer 16

1. A larger topology databse requires more memory on each router
2. The SPF algorithm requires processing that grows exponentially compared to the size of the topology database
3. A single interface status change anywhere in the internetwork (up to down, or down to up) forces every router to run SPF again

Question 17

Area Border Router (ABR)

Answer 17

An OSPF router with interfaces connected to the backbone area and to atleast one other area

Question 18

Backbone router

Answer 18

A router connected to the backbone area

Question 19

Internal router

Answer 19

A router in one area (not the backbone area)

Question 20

Area

Answer 20

A set of routers and links that shares the same detailed LSDB information, but not with routers in other areas, for better efficiency

Question 21

Backbone area

Answer 21

A special OSPF area to which all other areas must connect-area 0

Question 22

Intra-area route

Answer 22

A route to a subnet inside the same area as the router

Question 23

Interarea route

Answer 23

A route to a subnet in an area of which the router is not a part