Switching

[maheshpula109]

Hello,

if a PC-1 is connected to switchport(hostname of switch - switch 1 ) of vlan2 and suppose switch 1 is connected to switch 2 with trunk port.

Now,i know that PC cannnot understand vlan but when PC-1 sends a packet to switch 2 of any host(for eg. PC 2) in vlan 2 then

step 1) PC-1 would create a frame to and sent it to switch 1 considering it knows the mac address of PC -2 

step 2 ) switch 1 will know that PC - 1 is in vlan 2 as we wrote on that interface as switchport access vlan 2 and so on..

And my question is i have checked in cisco packet tracer capturing each packet sent on the switch - 1 interface by PC 1. I didnt saw any vlan PDU in that frame which is been received upon that interface of vlan 2 on switch -1.

How switch came to know that if any packet come across that vlan 2 interface it will be placed in vlan 2 mac address table of switch 1. How it knows ?? since there was not any kind of vlan tagging in that packet sent by PC to switch 1 .(PS - i know tagging is on trunk) 

[Joseph W. Doherty]

Usually the switch knows what VLAN an access port belongs to because, other then the default VLAN 1, it's assigned to the port with a configuration statement.

PS:

BTW, some PCs (servers usually) support VLAN tagging and can also connect to a trunk port.

[maheshpula109]

Yes agreed. But Cant we verify through any tool or some kind of debug which we can realize visually that how switch gets understand that ?? which we can realize this visually

[Joseph W. Doherty]

Unsure what you're trying to "see" visually and/or what you expect from tools.

Cisco's Packet Tracer isn't an 100% emulation of the devices it represents.

On the real devices, some of this information might be impossible to capture with any kind of (end user) tool or debug statement.  For example, you might not be able to capture/debug the actual process of a frame entering a switch and the switch checking whether the frame's source MAC is already known on that port, and if not, that MAC being associated with that port.  Indirectly, for a case like this, you can compare the before and after contents of the MAC table after a frame enters the switch.

[Dennis Mink]

The PC is not VLAN aware, it doesnt tag, as soon as the switch receives a layer2 frame in its port on switch 1 from PC1, from there on, based on your access vlan statement on that particular PC1 port, it marks/tags that incoming frame as being part of vlan 2 and switches it based on its CAM table. 

if that makes sense