Hands-On: Compare and Contrast IPEthernet and IPMPLSEthernet

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Hands-On: Compare and Contrast IP/Ethernet and IP/MPLS/Ethernet

If this is the only protocol analyzer present on your computer, you can open the file called MPLS_basic by clicking it. If you have another protocol analyzer, you have to open the Ethereal program and open the file from the menu.

1. From your desktop, go to Start | Programs; find and double-click Ethereal.

2. Once the Ethereal program opens, open the file called MPLS_basic.cap.

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

4. Find the frames that have 8847 in the protocol field (for example, Frame 9).

5. Follow the steps in the following exercise.

In protocol analyzers, we count bytes from left to right, starting at 0. So, if the first byte is said to have a value at offset of 0, the second byte is an offset of 1. In Figure 1.15, we see a standard IP-over-Ethernet packet.

1.	Look at Frame 1 in Figure 1.15. What is the value at offset 12 and 13? Figure 1.15: Frame 1
2.	Look at Frame 1 in Figure 1.15. What is the value at offset 14 and 15?
3.	Look at Frame 9 in Figure 1.16. What is the value at offset 12 and 13? Why is this value different? What does it mean? Figure 1.16: Frame 9
4.	Look at Frame 9 in Figure 1.16. What is the value at offset 14, 15, 16, 17? Translate the hex number into binary using the following chart. 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
5.	Determine the values for the following: The label __________ The experimental bits __________ The stack bit __________ The TTL value __________
6.	Look at offsets 18 and 19. What are their values?
7.	Compare the values in Questions 2 and 5. What do you find interesting about them?

Answers

1. 

The value at offset 12 and 13 is 0800 (the next header is IP).

2. 

45 CO (IP Version 4 with a 20 byte header and class of service)

3. 

8847  (A shim header next).

In Figure 1.15 frame 1, the note indicates that an IP header is next. In Figure 1.16, the note indicates that a shim header MPLS is next.

It means that the frame has been modified to accommodate MPLS.

4. 

00  1  1 f

Translate the hex number into binary using the chart below.

Label	E	S	TTL
0001D	0	1	FF

5. 

1. 29  

2. 0  

3. 1  

4. 255

6. 

45 00

7. 

MPLS was inserted and moved the start of the IP header by 32 bits.

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