Re: [Isis-wg] Jari Arkko's Discuss on draft-ietf-isis-node-admin-tag-10: (with DISCUSS)

["Les Ginsberg (ginsberg)" <[e-mail]>]

Alia –

How about replacing the second paragraph of Section 4.2 with:

“Node administrative tags are expected to be associated with a stable
attribute. In particular, node administrative tags MUST NOT be associated
with something whose state can oscillate frequently e.g., the reachability
to a specific destination.

While no specific limit on the number of node administrative tags which
may be advertised is defined, it is expected that only a modest number
of tags will be required in any deployment.”


   Les

From: Alia Atlas [mailto:[e-mail]]
Sent: Wednesday, May 04, 2016 5:22 PM
To: Les Ginsberg (ginsberg)
Cc: Jari Arkko; Peter Yee; [e-mail]; Christian Hopps; [e-mail]; The IESG; [e-mail]
Subject: Re: [Isis-wg] Jari Arkko's Discuss on draft-ietf-isis-node-admin-tag-10: (with DISCUSS)

Les & Peter,

True, one can have multiple Router Capability TLVs.

I do think that stable is a MUST.   I don't see a need for further clarification, but am happy to see other text.

As for small, I don't think that specifying an arbitrary number is needed.   At the same time, by specifying "small",
it's there's no expectation that this is a good way of transfering a database via IS-IS.

As I said, this is the same text as in the OSPF RFC and I do see it as both useful and close to sufficient.
Do you have more clear words to suggest?

Thanks,
Alia


On Wed, May 4, 2016 at 8:04 PM, Les Ginsberg (ginsberg) <[e-mail]<mailto:[e-mail]>> wrote:
Alia –

Sorry, have to jump in on this one.

The fact that IS-IS TLVs/sub-TLVs have an eight bit length only means that in a single TLV/sub-TLV the size is limited. This does NOT mean that multiple TLVs/sub-TLVs cannot be used to advertise the same type of data. The suggestion below that since no more than 250 bytes will fit in a sub-TLV therefore that limits the number of admin tags which could be advertised is therefore simply incorrect.

I did not follow closely the final review of RFC 7777 (apologies) but the choice of language “small and stable” is quite unfortunate. “Stable” is a legitimate concern of course. But “small” suggests that we need to limit the number of admin tags to some arbitrary number. I simply do not see the need to define that.

   Les


From: Isis-wg [mailto:[e-mail]<mailto:[e-mail]>] On Behalf Of Alia Atlas
Sent: Wednesday, May 04, 2016 3:46 PM
To: Jari Arkko
Cc: Peter Yee; [e-mail]<mailto:[e-mail]>; Christian Hopps; [e-mail]<mailto:[e-mail]>; The IESG; [e-mail]<mailto:[e-mail]>
Subject: Re: [Isis-wg] Jari Arkko's Discuss on draft-ietf-isis-node-admin-tag-10: (with DISCUSS)

Jari,

I think I need to push back a bit on this one.

I will note that the OSPF version of this same extension (RFC 7777)  uses exactly
this same text " Being part of the RI LSA, the Node Admin Tag TLV must be reasonably
   small and stable.  In particular, implementations supporting node
   administrative tags MUST NOT be used to convey attributes of the
   routing topology or associate tags with changes in the network
   topology (both within and outside the OSPF domain) or reachability of
   routes."
Of course, different reviewers find different concerns and that's quite reasonable.

The sentences following "small and stable" certainly provide guidance on
what is definitely not considered stable "In particular, but not
   limited to, implementations supporting the node administrative tags
   MUST NOT associate advertised tags to changes in the network topology
   (both within and outside the IS-IS domain) or the reachability of
   routes."

Since the total length of sub-TLVs is constrained to no more than 250 bytes
(as specified in RFC 4971 - a normative reference),I think it's clear that that the
data must be small.  While one can argue about how much of that space should
be consumed by Node Administrative tags, that does end up being a local domain decision.

I did see back and forth in the discussion between Peter and Pushpasis about
how specific to be in terms of what number to specify.  Are you looking for
clarification such as:

 "There are only 250 bytes [RFC4971-bis] available for sub-TLVs in the Router
Capability TLV; the maximum number of different Administrative Tags advertised
should be limited to permit other necessary sub-TLVs to be advertised.  The
decision on how many Administrative Tags are acceptable is a decision for the
deploying network."

Regards,
Alia

On Wed, May 4, 2016 at 5:12 PM, Jari Arkko <[e-mail]<mailto:[e-mail]>> wrote:
Jari Arkko has entered the following ballot position for
draft-ietf-isis-node-admin-tag-10: Discuss

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----------------------------------------------------------------------
DISCUSS:
----------------------------------------------------------------------

Peter Yee's Gen-ART review raised this issue which I agree with. Can this
be defined in a more clear fashion? Or is there already a definition
somewhere else that I had not seen?

Page 5, section 4.2, 2nd paragraph, 1st sentence: The sentence states:
"Being part of the Router CAPABILITY TLV, the node administrative tag
sub-TLV MUST be reasonably small and stable."  If you're going to make
this
a MUST, you've got to at least give a definition of "reasonably small"
and
perhaps even "stable" in the context of this specification.  As it
stands,
there's no test for whether the MUST is enforceable or understandable
between parties.