The MPLS WG Archive

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

"Feng, Mark" wrote:
> 
> The Label_Request object, with ATM Label Range, is used to set the
> "merge capable" and "label range" fields. If the node is non-merge
> capable, but do not wish to set a label range, what should be the
> minimum and maximum values within the object, since there is no
> flag within the object to indicate the absence of the range. Are
> there some special values?

An ATM interface always has a label range.  If your interface can really
any possible combination of VPI/VCI, then you can choose to use a range
that covers all possible UNI values:  VPI: 0-255, VCI: 0-65535.

You don't want to do this, though.  At the very least, you will want to
set a minimum VCI value of 32, since VCs 0-31 are always reserved for
ATM protocols - user-data connections like LSPs should not use them. 
Most ATM interfaces I know of have actual VPI/VCI range limits that are
imposed by the hardware and its configuration.

If you are talking about a shim-header interface (like POS), then merge
capability is assumed.  I don't think there is a way to tell your
neighbor that you have a non-merge-capable shim-header interface.

Also note that using an ATM-style label range object on a non-ATM
interface may cause your neighbor switch to reject the Path message.

I'm a bit interested in what this interface might be.  If you are using
shim headers, then there is no concern for cell-interleave (which is the
reason for not doing label merge on ATM interfaces).  It should be a
simple matter for two LSPs to swap their inbound labels to the same
outbound label if you have a non-cell interface.

-- David