Subject: label range

From: "Feng, Mark" <[email-masked]>
Date: Fri, 7 Sep 2001 15:13:04 -0700

Hi,

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?

Thanks in advance.

- Mark

---

From: David Charlap <[email-masked]>
Date: Fri, 07 Sep 2001 18:35:38 -0400

"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