Re: Freeform labels

[jcucchiara@mindspring.com]

-----Original Message-----
>From: Tom Petch <nwnetworks@dial.pipex.com>
>Sent: May 9, 2006 3:43 AM
>To: Adrian Farrel <adrian@olddog.co.uk>, ccamp@ops.ietf.org, tnadeau@cisco.com
>Cc: joan cucchiara <jcucchiara@mindspring.com>
>Subject: Freeform labels

Hi Tom,

>
>I am confused about freeform labels.  I am not familiar with them from other
>contexts and so am not clear how significant they are but ...
>
>(draft-ietf-ccamp-gmpls-)tc-mib under GmplsFreeformLabelTC references RFC3471
>which would be a good place to read about them except I can see no mention of
>them there.  They appear in tc-mib, lsr-mib and te-mib - they are used as worked
>examples which is what attracted my attention - but I cannot find them anywhere
>else in the (G)MPLS library.  I think that more description is needed somewhere.

The  GmplsFreeformLabelTC is also used in the GMPLS-LABEL-STD-MIB (gmplsLabelFreeform in the
gmplsLabelTable).  I believe given the purpose of this particular
MIB table and also within the context of the other objects in this
table, that the intent of GmplsFreeformLabelTC is fairly well described.

>
>Why does GmplsFreeformLabelTC give size limits of 0 and 64?  Can they really be
>0-length?  I have no problem with an SMI object having zero length as long as
>the entity being modeled by it can have zero length but is that meaningful here?
>And why 64? ok, a lot more than 32-bit but 64 sounds arbitrary (in which case, I
>think that worth saying); or does 64 octet relate to some other well known
>address formats (IPv6 anyone?).
>

The length of 64 was thought by the authors to be more than enough for the purpose
of this label.   I also questioned this during the MIB Dr. review, but currently label
lengths in the MPLS/GMPLS wgs are 4 octets, so 64 seems reasonable. 

0 length is used if this object does not contain a label, so it is not the actual label
that is 0 length, but when the object has not label.


>When GmplsFreeformLabelTC says 'not defined in any RFC',  I think it sums it up
>too well:-(
>

Yes, this is a MIB convention only.

>So the use of gmplsFreeformLabel(3) everywhere except in the formal definition
>where it appears (I assume) as gmplsFreeformGeneralizedLabel(3) seems about
>right as does the descripttion
>

Good catch.  I probably should have caught this during the MIB Dr. reviews.
Tom N. could you change this during the IESG/RFC reviews.


-Joan


>"The label is any form of label
>encoded as an OCTET STRING using
>the Textual Convention GmplsFreeformLabel"
>
>Well no, the Textual Convention is GmplsFreeformLabelTC and I would rather say
>that the label is encoded using the Textual Convention GmplsFreeformLabelTC
>(even though that is a redefinition of an OCTET STRING).
>
>I think more should be said somewhere, ideally in RFC3471, but, more
>realistically, in tc-mib.
>
>Tom Petch
>
>
>