Subject: RE: [Isis-wg] Last Call: IS-IS Extensions in Support of Generaliz ed MPLS to Informational RFC

From: Jon Berger <[email-masked]>
Date: Thu, 19 Jun 2003 10:07:22 +0100

I would like to suggest the following clarifications/corrections to this
draft before next week's deadline.

1.	For the Link Local/Remote ID sub-TLV:

In section 3.1 the draft specifies that this sub-TLV 'MUST NOT occur more
than once within the extended IS reachability TLV'.  The limitation should
actually be that the sub-TLV appear at most once per neighbor data
structure.

Likewise, where multiple instances of the sub-TLV are present, the draft
dictates that if the 'sub-TLV occurs more than once within the extended IS
reachability TLV, the receiver SHOULD ignore all these sub-TLVs'.  As well
as being incorrect for the reason stated above, I believe that this text is
slightly unclear as to whether the receiver should discard all of the
sub-TLVs, or just the superfluous ones (where my preference is the latter,
which allows the receiver to be generous, and is preferable to ignoring all
instances of the sub-TLV).  

My suggested replacement text for this section would be: 

'The Link Local/Remote Identifiers sub-TLV MUST NOT occur more than once per
IS neighbor data structure within the extended IS reachability TLV.  If the
Link Local/Remote Identifiers sub-TLV occurs more than once within an IS
neighbor data structure in an extended IS reachability TLV, the receiver
SHOULD ignore all bar the first of these sub-TLVs'.  

Note that this also corrects the misspelling of 'Identifiers'.

2.	For the Link Protection Type sub-TLV:

Section 3.2 is erroneous in the same way as section 3.1 - I suggest altering
the text to:

'The Link Protection Type sub-TLV MUST NOT occur more than once per IS
neighbor data structure within the extended IS reachability TLV.  If the
Link Protection Type sub-TLV occurs more than once within an IS neighbor
data structure in an extended IS reachability TLV, the receiver SHOULD
ignore all bar the first of these sub-TLVs'.  

3.	For SRLG TLVs I believe that the description of the flag byte should
include a comment specifically stating that the least significant bit
determines whether Link IDs or IPv4 addresses will be used in the TLV (bit
set to 1 - IP addresses, bit set to 0 - Link IDs).  

I propose adding the sentence: 'For a numbered interface, IPv4 addresses
SHALL be used to describe the link, whereas for an unnumbered interface Link
IDs SHALL be used.'

4.	For SRLG TLVs I think that it would be advisable to have the
following comment (as we do in the Link ID sub-TLV description): 'If the
Link Remote Identifier is unknown, it is set to 0.'

5.	In section 3.1 (the description of Link Local/Remote ID sub-TLVs),
the sentence ending '...followed by four octets of Link Remote Idenfier' has
a spelling mistake - should be IdenTIfier.

Regards,
Jon

Jon Berger
Data Connection Ltd
Email: [email-masked]
Web: http://www.dataconnection.com

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