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PAQPre-Assessment Quiz

Produced byMohamed BEN HASSINE

CNA InstructorThe American University of Paris

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1. What are the two main ways of classifying dynamic IGP routing protocols?

•Distance-vector•Link-state

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2. Which ones are also known as “shortest path first” protocols? Why?

Link-state, because that’s exactly what they do: they look for the shortest path to the destination (regardless of whether or not this is the BEST path).

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Q3. Fill in the following table:

Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector

Link State

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1

Link State

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2

Link State

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Link State

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Link State OSPF

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Link State OSPF IS-IS

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Easy to configure

Link State OSPF IS-IS

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Easy to configure Updates regularly

Link State OSPF IS-IS

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Easy to configure Updates regularly

Takes up significant bandwidth

Link State OSPF

IS-IS

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Easy to configure Updates regularly

Takes up significant bandwidth

Slow to converge

Link State OSPF IS-IS

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NA

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Easy to configure Updates regularly

Takes up significant bandwidth

Slow to converge Subject to routing

loops

Link State OSPF IS-IS

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NA

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Easy to configure Updates regularly

Takes up significant bandwidth

Slow to converge Subject to routing

loops RIP only has 1

metric

Link State OSPF IS-IS

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Easy to configure Updates regularly

Takes up significant bandwidth

Slow to converge Subject to routing

loops RIP only has 1

metric Only RIP v. 2 can

use VLSM Link State OSPF

IS-IS

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NA

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Easy to configure Updates regularly

Takes up significant bandwidth

Slow to converge Subject to routing

loops RIP only has 1

metric Only RIP v. 2 can

use VLSM Link State OSPF

IS-IS Only sends out updates as

needed

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NA

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Easy to configure Updates regularly

Takes up significant bandwidth

Slow to converge Subject to routing

loops RIP only has 1

metric Only RIP v. 2 can

use VLSM Link State OSPF

IS-IS Only sends out updates as

needed Doesn’t use much bandwidth to

maintain tables

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NA

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Easy to configure Updates regularly

Takes up significant bandwidth

Slow to converge Subject to routing

loops RIP only has 1

metric Only RIP v. 2 can

use VLSM Link State OSPF

IS-IS Only sends out updates as

needed Doesn’t use much bandwidth to

maintain tables Fast to converge

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NA

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Easy to configure Updates regularly

Takes up significant bandwidth

Slow to converge Subject to routing

loops RIP only has 1

metric Only RIP v. 2 can

use VLSM Link State OSPF

IS-IS Only sends out updates as

needed Doesn’t use much bandwidth to

maintain tables Fast to converge Not subject to routing loops

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NA

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Easy to configure Updates regularly

Takes up significant bandwidth

Slow to converge Subject to routing

loops RIP only has 1

metric Only RIP v. 2 can

use VLSM Link State OSPF

IS-IS Only sends out updates as

needed Doesn’t use much bandwidth to

maintain tables Fast to converge Not subject to routing loops Knows complete topology of

network so knows all routes

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NA

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Easy to configure Updates regularly

Takes up significant bandwidth

Slow to converge Subject to routing

loops RIP only has 1

metric Only RIP v. 2 can

use VLSM Link State OSPF

IS-IS Only sends out updates as

needed Doesn’t use much bandwidth to

maintain tables Fast to converge Not subject to routing loops Knows complete topology of

network so knows all routes Uses cost metrics instead of

distance metrics

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NA

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Easy to configure Updates regularly

Takes up significant bandwidth

Slow to converge Subject to routing

loops RIP only has 1

metric Only RIP v. 2 can

use VLSM Link State OSPF

IS-IS Only sends out updates as

needed Doesn’t use much bandwidth to

maintain tables Fast to converge Not subject to routing loops Knows complete topology of

network so knows all routes Uses cost metrics instead of

distance metrics Can use VLSM and CIDR

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NA

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Easy to configure Updates regularly

Takes up significant bandwidth

Slow to converge Subject to routing

loops RIP only has 1

metric Only RIP v. 2 can

use VLSM Link State OSPF

IS-IS Only sends out updates as

needed Doesn’t use much bandwidth to

maintain tables Fast to converge Not subject to routing loops Knows complete topology of

network so knows all routes Uses cost metrics instead of

distance metrics Can use VLSM and CIDR

Difficult to configure correctly

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NA

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Easy to configure Updates regularly

Takes up significant bandwidth

Slow to converge Subject to routing

loops RIP only has 1

metric Only RIP v. 2 can

use VLSM Link State OSPF

IS-IS Only sends out updates as

needed Doesn’t use much bandwidth to

maintain tables Fast to converge Not subject to routing loops Knows complete topology of

network so knows all routes Uses cost metrics instead of

distance metrics Can use VLSM and CIDR

Difficult to configure correctly

Requires more memory and more powerful CPUs in routers

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NA

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Type Protocol(s) Advantage(s) Disadvantage(s)

Distance Vector RIPv1 RIPv2 IGRP

Easy to configure Updates regularly

Takes up significant bandwidth

Slow to converge Subject to routing

loops RIP only has 1

metric Only RIP v. 2 can

use VLSM Link State OSPF

IS-IS Only sends out updates as

needed Doesn’t use much bandwidth to

maintain tables Fast to converge Not subject to routing loops Knows complete topology of

network so knows all routes Uses cost metrics instead of

distance metrics Can use VLSM and CIDR

Difficult to configure correctly

Requires more memory and more powerful CPUs in routers

Takes a lot of bandwidth when first started

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4. What are “hello” packets used for?

• Link state protocols use them to make sure a link is still active. They’re very small packets.

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5. What are the five things that link state protocols use to maintain their tables:

• Link-state advertisements (LSAs)• A topological database• The shortest path first (SPF) algorithm• The resulting SPF tree• A routing table of paths and ports to

each network to determine the best paths for packets

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6. What is meant by a “link” when talking about link state protocols?

• A link is an interface on a router.

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7. How does a link state protocol build its topological database? What kind of information is in it?

• It’s a database of the entire topology of the network and includes each link and how to reach it. It’s built by using the LSAs that have been received by the router.

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8. What are the three types of networks recognized by OSPF?

• Nonbroadcast multi-access (NBMA), such as frame relay

• Broadcast multi-access, such as Ethernet

• Point-to-point networks

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Q9. What is the DR and the BDR in an OSPF network? What do they do?

• DR – Designated Router acts as the “brains” of the network. This router makes sure that all the LSAs are sent to all the other routers in the Area.

• BDR – Backup Designated Router acts as the “second in command” of the network. If the DR goes down, the BDR takes over as DR. However, until the DR goes down, the BDR does not send out LSAs to any other routers in the Area.

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10. What is the multicast address used by the DR to send out LSAs to all other OSPF routers? For LSAs just to other designated (and backup) routers?

• 224.0.0.5• 224.0.0.6

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11. What is a hello packet used for and what is the multicast address used for it? Why this address?

• A hello packet is the way OSPF routers make sure that a link is still active. 224.0.0.5 is the address used so that all links are checked, not just DRs and BDRs.

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12. What is the default hello interval?

• 10 seconds

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13. What is the main area of an OSPF network designated?

• Area 0 (zero)

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14. What is the command used to start OSPF routing on a router?

• Router(config)#router ospf [process ID]

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15. What is the processor ID?

• It’s an identifier for the OSPF routing process on the router

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16. What is the command used to identify networks on an OSPF router?

• Router(config-router)#network [network no.] [wildcard-mask] area [area-id]

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17. What does an OSPF router use for its router ID? How can you force a different ID?

• It uses the highest active IP address on any of the interfaces (where OSPF is running). If you want to change the ID, set a Loopback interface with a higher IP address so it will be forced to be the ID.

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18. What is a Loopback?

• It is a logical (virtual) interface; not a physical (real) one

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19. What is the command used to set a Loopback?

• Router(config)#int Loopback[No.]• Router(config-if)#ip addr [IP number]

[subnet mask]

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20. What is the recommended subnet mask to use on a Loopback interface?

• 255.255.255.255

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Q21. What is a “priority” number used for? How can you change it?

• If there is more than 1 router in the Area (broadcast multi-access), then there must be a DR and maybe a BDR for the Area. The priority number is used to determine which routers will be the DR and the BDR.You can change it with the following command:

Router(config-if)#ip ospf [priority number]

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Q22. Why must you set the bandwidth on an interface running OSPF? What is the default bandwidth? How can you change it?

• Cost (the default metric of OSPF) uses bandwidth to determine the best route. The default is 1.544 Mbps. You can change it with the command:

• Router(config)#interface [type] [number]• Router(config-if)#bandwidth [Kbps]

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23. How can OSPF routers authenticate each other?

• They exchange passwords that only other OSPF routers will know. Use the commands below to set authentication:

• Router(config-if)#ip ospf authentication-key [password]

• Router(config-router)#area [area-number] authentication

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Q24. What is the difference between default authentication and a message-digest authentication procedure? What is the command to do the latter?

• The default authentication sends the password in plain text; message-digest encrypts the password that’s sent.

• Router(config-if)#ip ospf authentication message-digest-key [key-id] md5 [encryption-type key]

• Router(config-router)#area [area-id] authentication message-digest

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Q25. What is the relationship between the “hello” packet interval and the “dead” interval? What is meant by the “dead” interval?

• The dead interval is 4 times the hello interval (e.g., hello is 10 seconds, so dead is 40 seconds).

• The dead interval is the time used to determine that a link is down, or dead. In other words, if a hello isn’t received from a link for the space of 4 times the normal hello interval, it’s considered dead.

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Q26. What would happen if routers in the OSPF network have different hello intervals configured?

• They wouldn’t be able to “talk” to each other, so would be considered inactive. Hello intervals must be the same on all the routers in the network.

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27. What is the best way to define a default route on an OSPF router?

• Use the “quad zero” command:

Router(config)#ip route 0.0.0.0 0.0.0.0 [interface or IP address of next hop]

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Q28. How can you make sure that this information is propagated to other routers in the area?

• Router(config-router)#default-information originate

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Q29. List some of the show commands you can use to make sure that OSPF is functioning correctly.

• Show ip route• Show ip protocol• Show ip ospf interface• Show ip ospf• Show ip ospf neighbor [detail] (shows

neighbor database)• Show ip ospf database (shows topological

database)