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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.
From your desktop, go to Start | Programs and click Ethereal.
Once Ethereal opens, open the file called MPLS1.cap.
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.
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 |
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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. |
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3. | What are the values of each of the following for Label 1?
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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. |
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5. | What are the values of each of the following for Label 2?
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6. | Is the stack bit set for Label 1 (offset 14–17)? __________ |
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7. | Is the stack bit set for Label 2 (offset 18–21)? __________ |
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8. | Explain why the stack bit may be set differently. __________ |
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Answers
1. | 00 01 20 ff 00 01 01 ff 14 15 16 17 18 19 20 21 | ||||
2. |
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3. |
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4. |
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5. |
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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.
Answers: 1. C; 2. A; 3. D; 4. B. |
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