The MPLS WG Archive

[David Charlap <David.Charlap@marconi.com>]

Title:

Santanu.Ganguly@swisscom.com wrote:

Hi Shilpa,

 

1) I suspect what Roger means by 'as the router knows about all of them' is the following:

 

Generally speaking ther are 2 types of label spaces, as we all know: Per-Interface & Per-Platform. Per-platform assigns labels

from a platform-wide pool of labels and  uses resources that are shared across the platform. Hop-by-hop best-effort IP/MPLS

forwarding is an example of using the per-platform label space....

 

Frame based MPLS interfaces ( POS, Ethernet, fast Ethernet etc...:) use a per-platform label space , which basically means that the label space is router-wide and assigned from a unique pool of labels in the LSR; the label can used on ANY interface. The LFIB has no information about the incoming interfaces ( i think...:-))

 

However, the nature of the labels dolled out on LC-ATM interfaces stops us from using per-paltform label space. 2 LC-ATM interfaces can use the same VPI/VCI pair as a label. As such , LC-ATM interfaces use per-interface labels which has non-zero label space ID.

Note, however, that there is nothing in any standard mandating a
platform label space for Ethernet/POS or a per-interface label space
for LC-ATM.

Depending on the forwarding architecture (a centralized forwarding
engine vs. one distributed across all port-cards), it may make more
sense for a switch to use per-interface labels for Ethernet/POS, or
platform labels for LC-ATM.  This is perfectly legal.

While it is important to be aware of the different type of label
spaces, and to know what is commonly used, you should not assume that
"common" means "universally mandated".

-- David



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