Myths regarding Pure Ethernet:

The biggest myth being propagated regarding pure metro-ethernet or carrier ethernet is that there are 4094 VLANs available network wide for a provider network. This is simply not true. There are 4094 VLANs available on each switched path. So the VID(vlan id) cannot be reused along the path from point a to point z, but can be reused anywhere else in the network as long as the paths are separated.

Larger pure ethernet aggregation devices allow for traffic classification up to two tags deep. This allows for up to 16.7 million paths on a device of this nature, which should be used to aggregate devices that can only classify traffic based on 4094 VLAN ids.

So with proper network design, in most networks VLAN exhaustion is not an issue if the network is designed appropriately. The network should be designed so that devices supporting large MAC tables and traffic classification of two tags are interconnected, and they act as an aggregator for less expensive, smaller mac table, one tag switches in attached rings and segments. Attaching these devices to interconnect larger areas provides for the theoretic possibility of up to 16.7 million unique paths between these devices, limited only by the device processing and memory capabilities. In a properly designed geographically significant modular network, more expensive services such as MPLS and PBT can be postponed or eliminated entirely. VLANs are locally significant only.

December 17, 2011

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