The MPLS WG Archive

[Shahram Davari <Shahram_Davari@pmc-sierra.com>]

Hi James,


> > > Also, what was once a outer label could become an inner 
> label due to
> > > protection switching/path protection.
> > 
> > If we expect this to happen, we also need to use 
> per-platform label space
> > for the outer tunnel. 
> 
> If I understand you correctly, your answer to the original question
> (about MPLS-BGP labels), can be summarized as "clever label 
> allocation".
> 

Sorry James this was my mistake. In fact you don't need anything special and the previous rule that I mentioned is still valid: "Use per-platform label space for the inner label of tunneled packets"

First of all I assume by protection switching you meant using by-pass tunnels, otherwise you won't have label stacking. With this assumption, let me explain the solution to it by an example:

Assume the working path is F-A-B-C-D, and the protection path is F-A-E-C-D. Assume that labels L1,L2,L3,L4 are used for working path and labels L1,L5,L6,L4 are used for protection path. However to use the protection path as a bypass tunnel node A needs to swap label L1 to another label that has been distributed by C, which I call it X1. It is this X1 that should be from the per-platform label space of C. Label L3,L6 don't need to be from per-platform label space of C.



   L1      L2       L3       L4
F-------A-------B--------C---------D
	  |                |
         -------E--------              
           L5       L6
           X1       X1


Regards,
-Shahram