Saturday, August 26, 2006

 

OSPF Q & A -II

11: What is the significance of area 0?

***Area 0 is the backbone area. All other areas must send their inter-area traffic through the backbone.

12: What is MaxAge?

***MaxAge, 1 hour, is the age at which an LSA is considered to be obsolete.

13: What are the four OSPF router types?

***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: What are the four OSPF path types?

***The four OSPF path types are:

Intra-area paths

Inter-area paths

Type 1 external paths

Type 2 external paths


15: What are the five OSPF network types?

*** The five OSPF network types are:

i)Point-to-point networks

ii) Broadcast networks

iii) Non-broadcast multi-access (NBMA) networks

iv) Point-to-multipoint networks

v) Virtual links


16: What is a Designated Router?

***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: How does a Cisco router calculate the outgoing cost of an interface?

***Cisco IOS calculates the outgoing cost of an interface as 108/BW, where BW is the configured bandwidth of the interface.


18: What is a partitioned area?

***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: What is a virtual link?

*** A virtual link is a tunnel that extends an OSPF backbone connection through a non-backbone area.


20: What is the difference between a stub area, a totally stubby area, and a not-so-stubby area?

***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: What is the difference between OSPF network entries and OSPF router entries?

*** 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: Why is type 2 authentication preferable over type 1 authentication?

***Type 2 authentication uses MD5 encryption, whereas type 1 authentication uses clear-text passwords.


23: Which three fields in the LSA header distinguish different LSAs? Which three fields in the LSA header distinguish different instances of the same LSA?

***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.

Thursday, August 24, 2006

 

OSPF Q & A

1: What is an OSPF neighbor?

*** 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: What is an OSPF adjacency?

***An OSPF adjacency is a conceptual link to a neighbor over which LSAs can be sent.

3: What are the five OSPF packet types? What is the purpose of each type?

*** 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: What is an LSA? How does an LSA differ from an OSPF Update packet?

***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: What are LSA types 1 to 5 and LSA type 7? What is the purpose of each type?

*** 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: What is a link state database? What is link state database synchronization?

***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: What is the default HelloInterval?

***The default OSPF HelloInterval is 10 seconds.


8: What is the default RouterDeadInterval?

***The default RouterDeadInterval is four times the HelloInterval.


9: What is a Router ID? How is a Router ID determined?

***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: What is an area?

***An area is an OSPF sub-domain, within which all routers have an identical link state database.

Wednesday, August 23, 2006

 

Classes of IP addresses

1. To which class of IP address would the IP address of 197.22.103.221 belong?

A. class "A"
B. class "B"
C. class "C"
D. class “D”
E. class “E”

2. Which of the following dotted notations cannot represent an IP address?

A. 301.188.12.77
B. 167.78.35.202
C. 122.31.22.226
D. 254.254.254.254

3. In a class "A" network using an IP addressing scheme, the first sixteen bits are used for the network part of the address, and the last two octets are reserved for the host part of the address.

A. True
B. False

4. To what class of network would the following IP address belong: 144.26.108.15?

A. Class "A" network
B. Class "B" network
C. Class "C" network
D. Class “D” network

5. To what class of network would the IP address, 18.12.245.10, belong?

A. Class "A" network
B. Class "B" network
C. Class "C" network
D. Class “D” network

6. In the IP address, 190.233.21.12, how many octets have been assigned by the NIC?

A. One
B. Two
C. Three
D. Four

7. In the IP address, 88.224.73.201, how many octets could be assigned locally by the network administrator?

A. One
B. Two
C. Three
D. Four

8. Select the IP address below which would belong to the largest network.

A. 69.22.214.158
B. 144.144.144.3
C. 220.91.144.222
D. 255.255.255.255

9. Which of the following best describes a class "B" network?

A. network.network.host.host
B. network.network.network.host
C. network.host.host.host
D. host.network.host.network


10. There are three classes of commercial networks.

A. False
B. True

11. Which of the following is an example of a class "C" network address?

A. 196.25.10.0
B. 113.0.0.0
C. 11.3.22.104.0
D. 74.255.255.255

12. Which of the following best describes a class “C” network?

A. network.network.host.host
B. network.network.network.host
C. network.host.host.host
D. host.host.host.network

13. Which of the following best describes a class “A” network?

A. network.network.host.host
B. network.network.network.host
C. network.host.host.host
D. host.host.host.network

14. Which of the following is a class “C” IP address?

A. 220.15.64.126
B. 191.15.64.126
C. 127.15.64.126
D. 242.15.64.126

15. Select the IP address for the smallest network.

A. 220.15.64.126
B. 191.15.64.126
C. 127.15.64.126
D. 242.15.64.126

16. How many octets have been assigned by InterNIC in a class “C” network?

A. one
B. two
C. three
D. four

17. If you have a class “A” IP address, then how many bytes have been assigned to you for your hosts?

A. one
B. two
C. three
D. four

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