Prior to this study we refer to the principle of such a test https://blog.51cto.com/14451009/2427841 (GNS3 (the Cisco) use of trunk cross-switch configuration vlan). On the basis of this a successful experiment on our in-depth research works Trunk function using packet capture software.
See below, the following has been achieved across a trunk route using the divide with the PC1 PC3 to vlan 10, with the division of the PC2 to PC4 vlan20. The main purpose of this blog is to analyze the data frame with the PC1 to switch 1 sends the data to the switch 1 switch 2 transport frame What's different, now I'll grab a packet is sent to the switch 1 PC1 with a packet capture tool to see Look.
Here using PC1 to PC3 been a long ping command ping -t, then we click on the network cable connection between 1 PC1 with the switch, and use Wireshark packet capture tool to grab a packet of data to analyze, and to switch between the two then grab a network cable data, and then make a comparison between two data packets.
Here is to exchange data between the PC1 1.
Here is the data between the two switches.
FIG above two comparison we know, at the time of data through the switch 1 has been IEEE802.1Q protocol affixed to it an ID: tag 10, then we compare between the router 2 to the PC3 data. We found that out after 1 switch to the data label attached gone.
It can be concluded that, when using the inter-switch trunk function, from the time when the switch 1 receives the transmission data vlan 10 of the PC will automatically give it a part of a label affixed vlan 10 form a switch which can be recognized only It encapsulates IEEE802.1Q data protocol format, and this format can not be recognized by the PC. Therefore, a transmission from the switch with the switch 2 receives the encapsulated IEEE802.1Q the data protocol, it will be sent to this analysis vlan 10 is sent to the data vlan 20. Since switch 1 before it has been affixed to the label vlan10, the switch 2 will know the data to be sent to the vlan 10. Because the encapsulated IEEE802.1Q data protocol can not be recognized by the PC, so here put the switch 2 on the package label data to remove it, the final data is transmitted from PC1 to PC3 and PC2 vlan 20 not sent to the with PC4.