Cross-segment data communication flow

Verifying the data communication process with GNS3 and wireshask capture software

Real Test Map:

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The data communication process when the router R1 ping the router R3.

Steps:

① can view the MAC address of an interface by using the show Int f0/0 command.

The MAC address of the R1 f0/0 is: cc11.20f4.0000-----MAC1

The MAC address of the R2 f0/0 is: cc12.20f4.0000-----MAC2

The MAC address of the R2 f1/0 is: cc12.20f4.0010-----MAC3

The MAC address of the R3 f1/0 is: cc13.20f4.0010-----MAC4

② on the R1 pingR3----to analyze by grasping the bag

Just ping it once, command r1#ping 3.3.3.3 repeat 1

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Between the R1 and the R2 link L12 between the grab packet and the R2 and R3 grab packet, verify.

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ICMP request package for L12:

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ICMP Reply packet:

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ICMP request package for L23:

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It can be learned by the packet:

In the cross-network data communication, the transmission layer information is not changed, the source IP address of the network layer is not changed, but the TTL value of the IP head is skipped by 1, until the destination IP is reached. The checksum value is also changed.

The MAC address of the link layer package in the packet changes, as shown in the experiment:

R1--->r3 's mac package is:

L12:mac1 MAC2

L23:MAC3 MAC4

Summarize:

Flow of data across network segments:

Transport Layer: Unchanged

Network layer: The IP address is unchanged, the time-to-live TTL will be skipped by 1 (anti-ring function), the checksum will also change

Link Layer: Mac Source address network segment send rewrite

This article is from the "9305074" blog, please be sure to keep this source http://9315074.blog.51cto.com/9305074/1677508

Cross-segment data communication flow