[nsp] GE aggregation for last mile Ethernet

[Jack.W.Parks at alltel.com]

I've been doing research for deploying Catalyst for GE aggregation in
last mile Ethernet scenarios.  After scouring through CCO, it seems
there are two limits aside from physical port limitation.  This seems to
be common across the 3550/4500/6500 platforms.

* Limit 1 - Active VLANs

Although you have 4096 VLAN id's, you can only have ~1000 active VLANs.
In the extended VLAN range, it appears that each configured ext. VLAN is
assigned to a lower (1-1006) VLAN number. Cisco's recommendation is to
assign the >1000 VLAN ids starting at 1 and growing n+1.  For extended
VLAN ids, assignments should be made starting at 4096 and decrementing
by 1.  This is to prevent overlapping VLAN id's

* Limit 2 - PV+STP

The maximum number of Per VLAN Spanning Tree instances is 128. After you
grow past 128 VLANs you will need to configure MSTP and begin grouping
VLANs into common Spanning Tree instances.  If you haven't taken this
into consideration on initial deployment you could be reconfiguring your
network

Knowing these two limits you could potentially install a 6509 and only
use a couple ports before reaching the maximum active VLANs or changing
over to MSTP.  This would be a huge waste of capital.

My questions are: 
1) How do you size the switch?  Are other NSP's using Cat6506 w/ Sup1 or
beefing up the chassis to 6509 w/ Sup720?  
2) Do you limit the amount of VLANs per customer facing port (i.e. 100
per GE)? Potentially a customer could ask for 500 VLANs in a hub and
spoke topology effectively taking 1/2 of the available VLANs.
3) Inter-connecting switches seems across POPs seems ludicrous.  Would
there be a compelling reason to do this if you have an MPLS - L2VPN?
4) What is the average number of VLANs per GE port are others seeing out
there?

Thanks for your time...

Jack
 
Jack W. Parks IV
Sr. Network Engineer
ALLTEL Communications
jack.w.parks at alltel.com
Work: 501-905-5961
Cell: 501-680-3341