The MPLS WG Archive

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

Hi Eric,


1) Section 3 says: 
   "With this restriction in place, one should not distribute, to a
   particular label distribution peer, a binding of Explicit NULL to a
   particular FEC, unless the following condition (call it "Condition
   L") holds:  all MPLS packets received by that peer with an incoming
   label corresponding to that FEC contain only a single label stack
   entry.  If Explicit NULL is bound to the FEC, but Condition L doesn't
   hold, the peer is being requested to create illegal packets.  None of
   the MPLS specifications say what the peer is actually supposed to do
   in this case.  This situation is made more troublesome by the facts
   that, in practice, Condition L rarely holds, and it is not possible
   in general to determine whether it holds or not."

If an egress router does not distribute the explicit null label for a set of FEC elements, 
when it is not the egress LER for at least one of those FEC elements, then condition L always holds.   

Am I missing something?


Yours,
-Shahram 

>-----Original Message-----
>From: Eric Rosen [mailto:erosen@cisco.com]
>Sent: Monday, January 05, 2004 2:15 PM
>To: mpls@UU.NET
>Subject: Correction of Explicit Null specification in RFC 3032
>
>
>I would like to call the WG's attention to the following draft: 
>
>        draft-rosen-mpls-explicit-null-01.txt
>
>Abstract
>
>   RFC 3032 defines a reserved label value known as "IPv4 
>Explicit NULL"
>   and a reserved label value known as "IPv6 Explicit NULL".  It states
>   that these label values are only legal at the bottom of the MPLS
>   label stack.  This restriction is now removed, so that those label
>   values are legal anywhere in the stack.
>