Hands-On: Open the File and Review File Content

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If you are the “hands-on” type and you want to see MPLS packets on a protocol analyzer, you need the two items of software (Ethereal and the MPLS-basic-cap sample) mentioned in the previous hands-on exercise.

  1. From your desktop, go to Start | Programs and click Ethereal.

  2. Once Ethereal opens, open the file called MPLS1.cap.

  3. Wait for the file to open. It will take a few minutes.

The file should look like Figure 1.17. Now let’s review the file content in the following steps.

click to expand
Figure 1.17: Open MPLS_basic File

1. 

Look at Frame 9, as shown in Figure 1.17. Note the values found at offsets 14 to 21. Record them in hex here:

_____  _____  _____  _____  _____  _____  _____  _____ 14     15     16     17     18     19     20     21

 00 01 20 ff 00 01 01 ff 14 15 16 17 18 19 20 21

2. 

Using the following chart, translate the hex number into binary for Label 1 found at offsets 14–17.

128 64 32 16 8 4 2 1.  128 64 32 16 8 4 2 1.   128 64 32 16 8 4 2 1. 128 64 32 16 8 4 2 1.

3. 

What are the values of each of the following for Label 1?

  1. The label __________

  2. The experimental bits __________

  3. The stack bit __________

  4. The TTL value __________

 a. 18 b. 0 c. 0 d. 255

4. 

Using the following chart, translate the hex number into binary for Label 2 found at offsets 18–21.

128 64 32 16 8 4 2 1.  128 64 32 16 8 4 2 1.   128 64 32 16 8 4 2 1. 128 64 32 16 8 4 2 1.

 label e s ttl

5. 

What are the values of each of the following for Label 2?

  1. The label __________

  2. The experimental bits __________

  3. The stack bit __________

  4. The TTL value __________

 a. 16 b. 0 c. 1 d. 255

6. 

Is the stack bit set for Label 1 (offset 14–17)? __________

 off

7. 

Is the stack bit set for Label 2 (offset 18–21)? __________

 on

8. 

Explain why the stack bit may be set differently. __________

 the stack bit is turned on to indicate that this is the last header in the stack (or the header closest to the ip header).

Answers

1. 

00   01   20   ff   00   01   01   ff

14   15   16   17   18   19   20   21

2. 

click to expand

3. 

  1. 18  

  2. 0  

  3. 0  

  4. 255

4. 

Label

E

S

TTL

5. 

  1. 16  

  2. 0  

  3. 1  

  4. 255

6. 

OFF

7. 

ON

8. 

The stack bit is turned on to indicate that this is the last header in the stack (or the header closest to the IP header).

Checkpoint 

Match the lettered item with its appropriate numbered description.

1.

____ is the path

A.

LER

2.

____ pushes, pops labels

B.

FEC

3.

____ swaps labels

C.

LSP

4.

____ traffic class

D.

LSR

Answers: 1. C; 2. A; 3. D; 4. B.



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Rick Gallagher's MPLS Training Guide. Building Multi-Protocol Label Switching Networks
Rick Gallahers MPLS Training Guide: Building Multi Protocol Label Switching Networks
ISBN: 1932266003
EAN: 2147483647
Year: 2003
Pages: 138

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