Vlan tagging

[sandy1]

Can two Cisco L2 switches (one managed by us - other one managed by client) use different L2 vlans numbers in between the access link to connect and pass traffic? 

[Flavio Miranda]

Hi @sandy1

 If I understood correctly, no. When the frame from your side cross the trunk between switches and get in the other side, the switch will try to put that frame on the vlan tagged, but, that vlan does not exist on that switch.

You can easily simulate this by using Packet Tracer. Find attached a lab for that, just rename it for .pkt

-If I helped you somehow, please, rate it as useful.-

[sandy1]

Yes, so might be need to make the switch to switch connectivity an access port, so the connection will go untagged. 

[Flavio Miranda]

If you have vlan on both sides then there will be tag. The only way to send untagged is using native vlan on both side.

  I didn't try that but you can try put both vlans as native and see what happen.

-If I helped you somehow, please, rate it as useful.-

[sandy1]

i tried in lab. it works. I mean mark the switch to switch port as "access" port and as a member of a vlan,

switch 1 : access vlan 10

switch 2: access vlan 20

[Joseph W. Doherty]

Yes, that's expected behavior. As long the frame is untagged, you can move frames between VLANs using access ports (using different VLANs).

Additionally, you could also do it on trunk ports, using the "native" (i.e. untagged) VLAN. I.e. the native VLAN could be different between trunks, but again, untagged frames can flow between different VLANs.

Also BTW, you could do this on the same switch.

Lastly, Cisco switches with CDP enabled, should generate log messages there's a VLAN mismatch.

[Zain Khan]

Hi @sandy1

in some cases it is possible that user and your vlan can pass traffic with each. by default Vlan behaviour does not allow to communicate with each other but you can allow specific vlan to communicate each other by using Trunk link 

when you will make the link trunk those vlan which you want to communicate with each other can be allowed by 

#switchport mode trunk 

#Switchport trunk allowed vlan x,x,x,x