The MPLS WG Archive

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

Irfan Lateef wrote:
> 
> With the current experience with MPLS, and the need to design
> high speed MPLS routers, I would like take your suggestion to
> the extreme of saying that we should have only 16-bit labels.
> This would allow faster label lookups. Hence it brings me to saying
> that 32-bit MPLS label itself is actually a disadvantage in taking
> the designs to the next levels.

MPLS labels are not 32-bit values.  They are stored in 32-bit integers
for the convenience of signaling protocols.

An MPLS label on an interface that uses shim headers (like POS) is 20
bits wide.

An MPLS label on an ATM interface may be 8, 12, 24 or 28 bits, depending
on the encoding scheme (SVC or SVP) and whether the cell structure is
UNI or NNI.  In general, I think most implementations use 24-bit labels
(SVC encoding with UNI-format cell structures.)

An MPLS label on a Frame Relay interface may be 10 or 23 bits, depending
on the DLCI width that the interface uses.

See also RFCs 3031, 3032 and 3034

-- David