The MPLS WG Archive

["James R. Leu" <jleu@mindspring.com>]

Hello Eric,

<snip>
> In fact, there is no such thing as a per-platform label space of VPI/VCIs or
> DLCIs.  So  there is  no way  a per-platform label  space could  take values
> away from a per-interface label space in an ATM-LSR. 

This question is slightly tangential, but:

How does one handle the case where you have ATM and POS interfaces terminating
"tunnels" which carry traffic with a label value for the same service?

<snip>
> One problem  with this proposal  is that  there is no  such notion as  an "N
> level label". 

If the stack consists of 2 labels.  The bottom label is is the 2nd level label.
When allocating that bottom label, the service should take into consideration
which set of top labels could be used to "tunnel" traffic with that label
value to this LSR.

> James> In  the current  drafts  the  only way  to  have multiple  interfaces
> James> sharing the  same label space is for  them to all be  assigned to the
> James> per-platform  label space.   To do  this  box wide  though, could  be
> James> opening the box up to security issues (think spoofed MPLS packets). 
> 
> The fact that  all interfaces use labels from the same  label space does not
> imply that an incoming packet with a label from that space must be accepted,
> irrespective of  the interface on which  it arrives.  If  a particular label
> has not been distributed to any  label distribution peer that can be reached
> out interface I, then packets arriving  over interface N with that label can
> be discarded as bogus. 

So you are saying that even though interface I,N are members of the
platform label space, the contents of their ILMs may be different.
Agreed.  There are cases though when the labels allocated from the platform
label space need to be added to the ILMs of multiple interfaces.  How will
the user specify _which_ interfaces should be included?  Most likely by
creating a group of interfaces, and associating that group with a service.
Why not use the label space for the grouping and the association?

> Perhaps  this is exactly  what you  are getting  at above  -- that  for each
> label, it is  helpful to know the set of interfaces  over which traffic with
> that label may be validly received.  

<snip>
> Unless you  have some reason  for using the  same label value  for different
> services, there  is no difference  between having per-service  label spaces,
> and having a per-platform label space where you know that certain labels may
> not be validly  received over certain interfaces.  What you  need to know is
> that a  particular label has been  used for a particular  service, you don't
> really need a per-service label space.

I'm assuming we will need more then 20 bits to represent all of the label
values allocated by a given LSR.

Jim
-- 
James R. Leu