VLAN Tag 1

[Microbyte]

Hi!

Our company have 2 3550 switches connected with VTP with each VLAN per port.
Port 1 = VLAN 101
Port 2 = VLAN 102
and so on..

My question is if the data is traveling from port 1 on switch A which goes through the trunk and comes out of port 1 on switch B (VLAN 101). Does that data carries any evidence of VLAN tagging?
I mean does the receiving side needs to put the header tag off (or any VLAN tagging residue) for proper transmission?

Thanks for all your help!


Microbyte

 

[IPKONFIG]

Not sure what your asking, but if you're wanting to know if your frames are being tagged when going across the trunk then the answer is yes. You shouldn't have to do any special configuration for communication to work. If both ports that are wanting to communicate with each other are in the same vlan then they see each other as being on the same subnet and they will communicate fine. If you wanting to go between subnets then you'll need a L3 device/connection to be able to do this. Like port 2 on switch A talking to port 8 on switch B.

"I can picture a world without war. A world without hate. A world without fear. And I can picture us attacking that world, because they'd never expect it."
- Jack Handey, Deep Thoughts

 

[Microbyte]

Let me rephrase:

PC 1 - Switch A (3550) - Switch B (3550)- Switch C - Switch D - PC 2

Switch A and Switch B ports are VLAN tagged.
Would frames coming out of switch B ports onto Switch C sees the frame tagged with VLAN?


Microbyte

 

[lui3]

here is how it works.

data from port 1 on switch one is sent from the host to the switch port which has been assigned to vlan 101. Once the data frame enters port 1 it is encapsulated with VLAN tagging information(with ISL this is 20+ bytes and with 802.1q the frame is modified and 4 bytes are added). If the vlan 101 is the native vlan then no modification is made to the data frame. But for explanation purposes lets assume that the vlan 101 is not the native vlan. So now you have data in the port buffer of switch 1 port 1 belonging to vlan 101 and encapsulated as such. now the switch looks up the destination address of the frame and forwards it along the destination. If the destination address lies on a port belonging to vlan 101 that is local to the switch then the data frame goes in port 1 (vlan 101) and out the destination port # (also belonging to vlan 101).

in the caae of trunking the destination port lies off of another switch that has been connected to the local switch via a trunked port. this port is capable of carrying multiple vlan tagged frames along its path without intermixing the frames. Now the frame is sent along the trunk where the destination switch looks up the destination address of the frame and locates the destination port belonging to that vlan. The switch forwards the frame across its backplane still preserving the vlan data until it gets to the transmit buffer of the destination port where the vlan tagging information is stripped from the frame and the original data frame is delivered to the destination host. No vlan tagging information will be present in the frame once it reaches the destination host.

in the rare case that the destination host has the ability to trunnk and the switch is aware of this then the destination host would be able to see vlan tagging information.

hope this long winded explanation helps.


Lui3
CCNP,CCDA,A+/Net+
Cisco Wireless Specialization

 

[lui3]

PC 1 - Switch A (3550) - Switch B (3550)- Switch C - Switch D - PC 2
Switch A and Switch B ports are VLAN tagged.
Would frames coming out of switch B ports onto Switch C sees the frame tagged with VLAN?

If switch C port was configured to trunk then it would see the vlan tag. If switch B was configured as an access port and not a trunk port the vlan tag would be stripped off the data frame prior to being sent to switch C.

However, if you left the switches at their defaults and they are 2950s and 3550s they will autonegotiate trunking on uplink ports. So either scenario is possible.

Lui3
CCNP,CCDA,A+/Net+
Cisco Wireless Specialization

 

[Microbyte]

Thanks alot Lui!


Microbyte