[c-nsp] Unable to connect VLAN traffic

[Jay Hennigan]

Johnny Ramirez wrote:
> Justin,
>  
> I appreciate your well explained answer. So basically they would tell me what VLANs I should use for me to match them.

Maybe.  When you have multiple VLANs on the same interface, Cisco calls 
this a "trunk".  Other vendors may define "trunk" differently, such as 
LACP/PAGP, so beware of terminology issues with the carrier.

In order to carry multiple VLANs and sort them out at the other end, 
frames on each VLAN have a "tag" in the header which is used by the 
receiving switch to identify the VLAN.

Your transport provider is probably using this technology to service 
multiple customers.  Within the provider's network, your frames are 
tagged with a VLAN-id unique to you as a customer.  The tag is stripped 
at the other end.

Thus, the transport provider isn't expecting to see a VLAN tag on your 
traffic, as it uses VLAN tags internally to distinguish between 
customers.  When you send tagged frames the transport provider either 
strips your tags or discards the frames to avoid confusion with its 
customer-identifying tags.

Your choices:
1. Define all of the VLANs you'll use, hope they don't conflict with 
those for other customers, and ask the provider to pass your tags.  This 
is messy and doesn't scale.

2. Ask your carrier to provision the circuit as "Q-in-Q" (802.1q with 
your tags inside 802.1q with their tags).  Think postal mail with an 
envelope inside an envelope.  This scales, the transport provider 
doesn't care what's written on the inside envelope.

--
Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
Impulse Internet Service  -  http://www.impulse.net/
Your local telephone and internet company - 805 884-6323 - WB6RDV