[nsp] remapping VLAN IDs between .1q trunk ports on the 3550?

Andrew Fort afort at choqolat.org
Fri Sep 19 17:24:31 EDT 2003

Sean Mathias said the following on 18/09/2003 4:13 PM:

> Have a look at 802.1q tunneling.
> Sean 

Sean, I dont think 802.1q tunneling is what I'm after, but please 
correct me if I'm wrong...

What I'm talking about is having two (ethernet) SPs connecting via a 
switch (in this case, a c3550-EMI).  They might connect because one 
provider (A) can provide physical tails where the other provider cannot 
(B), so they enter into an agreement where (A) provides (B) with tails 
for customers of (B) to use (so that (B) can get greater customer reach).

For the case of the example, one provider (lets say, B) uses VLAN ranges 
100-200 for their customers, but those VLAN numbers are already in use 
at (A), so they will be using 1500-1600 for (A)'s customers.

What I'd like to be able to do is, on the port where (A) connects to 
(B)'s switch:

interface GigabitEthernet0/1
  description Customer Interconnect with (A) xl-sw1.popname Gi1/14
  no ip addr
  switchport mode trunk
  switchport trunk encap dot1q
! magic (made-up) command
  switchport trunk vlan map id 1500 to 100
  switchport trunk vlan map id 1501 to 101
  switchport trunk vlan map id 1502 to 102
and so on.

You'd probably also need similar (reversed) configuration on the other 
port (on the trunk port going to (B)'s ethernet network).

Now I've seen a feature where by you can re-map the VLAN IDs used by ISL 
reserved VLAN IDs to something else, but the ID range you can re-map is 
very limited (since the feature is designed for this specific purpose).

What we need is a way to do the above for an arbitarily large number of 
VLANs (or at least say 64), without resorting to individual access ports 
per customer, of course.

Is this possible?  Surely other metro ethernet providers have been 
demanding this feature?  How do you do it right now?

I've heard this is possible with the 'purple' ethernet switch vendor, 
can anyone comment on that (off-list is fine since we're heading OT there)?


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