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Internetworking with TCP/IP: Pearson New International Edition

Douglas E. Comer

Chapter 14

Routing Within An Autonomous System (RIP, RIPng, OSPF, IS-IS) - all with Video Answers

Educators

Chapter Questions

Problem 1

What network families does RIP support? Why?

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Problem 2

Consider a large autonomous system using an IGP that bases routes on delay. What difficulty does the autonomous system have if a subgroup decides to use RIP on its routers? Explain.

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Problem 3

Within a RIP message, each IP address is aligned on a 32-bit boundary. Will such addresses be aligned on a 32-bit boundary if the IP datagram carrying the message starts on a 32-bit boundary? Why or why not?

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Problem 4

An autonomous system can be as small as a single local area network or as large as multiple wide area networks. Why does the variation in size make it difficult to define a single IGP that works well in all situations?

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Problem 5

Characterize the circumstances under which the split horizon technique will prevent slow convergence.

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Problem 6

Consider an internet composed of many local area networks running RIP as an IGP. Find an example that shows how a forwarding loop can result even if the code uses "hold down" after receiving information that a network is unreachable.

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02:40

Problem 7

Should a host ever run RIP in active mode? Why or why not?

Danielle Ashley
Danielle Ashley
Numerade Educator

Problem 8

Under what circumstances will a hop count metric produce better routes than a metric that uses delay?

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Problem 9

Can you imagine a situation in which an autonomous system chooses not to advertise all its networks? (Hint: think of a university.)

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Problem 10

In broad terms, we could say that an IGP distributes the local forwarding table, while BGP distributes a table of networks and routers used to reach them (i.e., a router can send a BGP advertisement that does not exactly match items in its own forwarding table). What are the advantages of each approach?

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Problem 11

Consider a function used to convert between delay and hop-count metrics. Can you find properties of such functions that are sufficient to prevent forwarding loops? Are the properties necessary as well?

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Problem 12

Are there circumstances under which an SPF protocol can form forwarding loops? (Hint: think of best-effort delivery.)

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Problem 13

Build an application program that sends a request to a router running RIP and displays the routes returned.

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Problem 14

Read the RIP specification carefully. Can routes reported in a response to a query differ from the routes reported by a routing update message? If so how?

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Problem 15

Read the OSPFv2 specification carefully. How can a manager use OSPF's virtual link facility?

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02:23

Problem 16

OSPFv2 allows managers to assign many of their own identifiers, possibly leading to duplication of values at multiple sites. Which identifier(s) may need to change if two sites running OSPFv2 decide to merge?

Alexander Clippinger
Alexander Clippinger
Numerade Educator

Problem 17

Can you use ICMP redirect messages to pass routing information among interior routers? Why or why not?

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02:32

Problem 18

Read the specification for OSPFv3. What is a stub area, and what is a not so stubby area (NSSA)? Why are the two important?

CD
Christine Doronio
Numerade Educator

Problem 19

What timeout does the OSPFy3 standard recommend for a Hello interval?

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Problem 20

Write a program that takes as input a description of your organization's internet, uses SNMP to obtain forwarding tables from all the routers, and reports any inconsistencies.

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Problem 21

If your organization runs software such as gated or Zebra that manages multiple TCP/IP routing protocols, obtain a copy of the configuration files and explain the meaning of each item.

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