Networking Explained, Second Edition > Network Hardware Components (Layers 1 and 2) > 39. Can you give me an example of what you mean by a network loop? - Pg. : Safari Books Online

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Networking Explained, Second Edition

Networking Explained, Second Edition

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Contents

Ch. 1. Fundamental Concepts of Computer Networks and Networking

Ch. 2. Network Topologies, Architectures, and the OSI Model

Ch. 3. The Internet and TCP/IP

Ch. 4. Physical Layer Concepts

Ch. 5. Data Link Layer Concepts and IEEE Standards

Ch. 6. Network Hardware Components (Layers 1 and 2)

1. What are connectors?

2. Gender? What does gender have to do with connectors? Do connectors have sex?

3. Referencing Figure 6.1, what’s the difference between an eight-pin modular connector and an RJ-45 connector, which looks a like modular telephone “jack”?

4. What connectors are used for coax cable?

5. How about fiber-optic cable?

6. What about a printer cable connector or a modem cable connector? Do they also operate at the physical layer?

7. OK. Enough about connectors. Let’s move on to transceivers. What are they?

8. Given the name, transceivers presumably transmit and receive signals. Right?

9. Exactly where is a transceiver located in a network? Is it a separate device? Is it built into the computer? Where is it?

10. Could you expand on the notion of AUI, please?

11. Are AUI connectors the ones that have those weird slide-lock things on them that never seem to work?

12. OK. I now understand AUI, but what do AAUI and MAU mean?

13. Enough about transceivers. Let’s talk about repeaters

14. Give me a little more detail. Where are they used? Why are they used?

15. Do repeaters introduce delay in a network?

16. Are repeaters also called hubs?

17. What about a stackable hub? What’s that?

18. So what you are saying then is that when I hear the term “Ethernet hub” I shouldn’t assume it is a repeater

19. Is there anything else I need to know about repeaters?

20. Are there any other layer 1 devices I should know about?

21. What devices operate at the data link layer?

22. I am familiar with network interface cards. These are Ethernet cards, right?

23. This is confusing

24. I see. It’s a semantic thing. You have the generic name—network adapter—and the specific name—Ethernet card. But don’t all NICs do the same thing?

25. Can you give me an example?

26. Earlier you said that transceivers are usually built directly into a network interface card. Doesn’t this make a NIC a layer 1 device also?

27. Are NICs part of a computer system, or do they have to be installed separately?

28. What does a NIC installation involve?

29. What do you mean by “special network ‘driver’ software”?

30. Are all NICs the same? In other words, does it matter which brand I purchase?

31. So what do I need to consider when purchasing a NIC?

32. I have a laptop computer and use a PC card for network connectivity. Is this considered a NIC?

33. Can you tell me a little more about PC cards? Are they same as PCMCIA cards?

34. Let’s move on. From the list of layer 2 devices given earlier we still haven’t talked about bridges and switches. What are they?

35. What do bridges do?

36. How does a transparent bridge work?

37. How does a source-routing bridge differ from a transparent bridge?

38. I have heard the term “spanning tree” used with bridges. What does this mean?

39. Can you give me an example of what you mean by a network loop?

40. So how does the spanning tree algorithm help?

41. Does it matter what network protocol you are using when you install a bridge?

42. I have heard the term “store-and-forward” used when discussing bridges. What does this mean?

43. If I had to choose between using a repeater or a bridge, which should I select?

44. Does replacing a repeater with a bridge improve Ethernet LAN performance?

45. What’s a brouter?

46. OK. Let’s move on to switches. What are they and how different are they from bridges?

47. Yes. Are there others?

48. Back to Ethernet switches, please

49. It sounds like an Ethernet switch is the same as a bridge except for its name. What’s different about switches?

50. What are the various types of switches?

51. Is a store-and-forward switch the same thing as a store-and-forward bridge?

52. What’s different about the cut-through architecture?

53. What’s a hybrid switch?

54. How does the performance of bridges and switches compare?

55. How does the performance of different switch architectures compare?

56. Besides the switching fabric, is there anything else I need to know about switches to increase my switch-knowledge coefficient?

57. I have heard and read about “layer-3 switching” and “layer-3 switches.” Frankly, I am a little confused by these concepts. Could you shed some light on this?

End-of-Chapter Commentary

Ch. 7. Internetworks and Network Layer Concepts and Components

Ch. 8. Ethernet, Ethernet, and More Ethernet

Ch. 9. Token Ring

Ch. 10. Fiber Distributed Data Interface (FDDI)

Ch. 11. Integrated Services Digital Network (ISDN)

Ch. 12. Frame Relay

Ch. 13. Switched Multimegabit Data Service (SMDS)

Ch. 14. Asynchronous Transfer Mode (ATM)

Ch. 15. Dialup and Home Networking

Ch. 16. Network Security Issues

Ch. 17. Network Convergence

Ch. 18. Wireless Networking

Appx. A. Vendor Ethernet/802.3 Prefixes

Appx. B. Using Parity for Single-Bit Error Correction

Appx. C. Guidelines for Installing UTP Cable

Appx. D. Network Design and Analysis Guidelines; Network Politics

URL

Help

39. Can you give me an example of what you mean by a network loop?

Sure. Look at Figure 6.17, which has four network segments interconnected by four bridges. LAN 1 is connected to LAN 2 by B1; LAN 2 is connected to LAN 3 by B2; and LAN 3 is connected to LAN 4 by B4. Note also that LAN 1 is connected to LAN 4 by B3. Thus, multiple bridges are being used on LAN 1. Let us assume that a frame originates on LAN 1 and none of the bridges (B1-B4) has an entry for the frame’s destination. Here is an example of how a network loop can develop:

Figure 6.17. A possible network loop.

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