vlans and tags 1

[just1moretime]

I have been told vlan tags are locally important
only. This seems counter intuitive to me. It seems like
if I send out packets tagged with vlan id of 1 that they
could be routed or sent to other switches vlan 1. And if
they were both not in the same subnet, they would not be able to communicate.
ie- switch a vlan 1 170.170.170.1 /24 mask
switch a vlan 2 170.170.171.1 /24 mask

switch b vlan 1 170.170.170.1 /24 mask
switch b vlan 2 180.180.180.1 /24 mask

In this example switch a vlan 1 to switch b vlan 1, ok
to communicate. But switch a vlan 2 to switch b vlan 2, no
communication. Thanks for your time.

 

[VinceWhirlwind]

That's correct. If you want switches a & b to be on the same physical network you *should* have a universal VLAN/subnet scheme for the network.

 

[Silverblade]

Indeed you are totally correct.
For vlans or different subnets to communicate with eachother you'll need a router.

 

[ADB100]

You have to look at the bigger picture. VLAN Tags are only significant within the Layer-2 domain; as soon as they reach a Layer-3 boundary (the gateway or next-hop) and get routed then the 802.1q VLAN header is discarded.

If you have big Layer-2 domains and VLANs spanning a large network then you have a problem..... Draw a picture of the topology.

Andy