[Lsr] Benjamin Kaduk's No Objection on draft-ietf-lsr-ospf-prefix-originator-10: (with COMMENT)

Benjamin Kaduk via Datatracker <noreply@ietf.org> Wed, 07 April 2021 06:08 UTC

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Subject: [Lsr] Benjamin Kaduk's No Objection on draft-ietf-lsr-ospf-prefix-originator-10: (with COMMENT)
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Benjamin Kaduk has entered the following ballot position for
draft-ietf-lsr-ospf-prefix-originator-10: No Objection

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COMMENT:
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In the ECMP case is there a way to correlate (order of appearance?) the
listed router-IDs with the listed reachable addresses?

Are there cases where you might choose to only advertise one but not the
other of the prefix source Router-ID and address?

Section 2.1

   The parent TLV of a prefix advertisement MAY include more than one
   Prefix Source OSPF Router-ID sub-TLV, one corresponding to each of
   the Equal-Cost Multi-Path (ECMP) nodes that originated the given
   prefix.

Is there any subtlety (or complexity, I guess) to how the advertising
node knows about the other ECMP nodes advertising the same prefix?  For
example, would there be some transient discovery stage when first
setting up the ECMP advertisement and only a subset of the ECMP nodes
are actually listed in some advertisements that go out?

Section 3

   another non-backbone area.  The ABR performs its prefix calculation
   to determine the set of nodes that contribute to the best prefix
   reachability.  It MUST use the prefix originator information only
   from this set of nodes.  The ABR MUST NOT include the Prefix Source
   OSPF Router-ID or the Prefix Source Router Address Sub-TLVs when it
   is unable to determine the information of the best originating node.

I feel like this text might be hiding some subtlety as to the nature of
determining the "nodes that contribute to the best prefix reachability"
-- is this a concept that is well established in the core OSPF RFCs
already (and thus doesn't need further explanation)?

Section 4

We often consider privacy considerations as part of the security
considerations section.  Since routers are to some extent inherently
"well known", they themselves may not have much privacy considerations
but there may be something to say about propagating additional
information about the internal structure of a given network.  My
understanding is that OSPF areas are all under a common administrative
domain, so this mostly only seems relevant to the case of AS-external
advertisement.  One potential consideration would be if there is value
in hiding that a set of prefixes are all advertised by the same router
(the "linkability" of the prefixes, if you well).
(Hmm, I guess this is somewhat related to the existing operational
considerations discussion, but not entirely equivalent.)

If we go into more detail on potential use cases, we might accordingly
be able to go into more detail on the consequences of a rouge node
injecting incorrect prefix source information.

Section 5

   protocol.  Based on deployment design and requirements, a subset of
   prefixes may be identified for which the propagation of the
   originating node information across area boundaries is disabled at
   the ABRs.

Per my previous comment, is this even more important at ASBRs than ABRs?

NITS

Section 1

   The identification of the originating router for a prefix in OSPF
   varies by the type of the prefix and is currently not always
   possible.  [...]

(nit) my intuition is suggesting that the intent is that the "procedures
for identification" vary and are not always possible; is that correct?
(It seems to me that "the identification of the originating router
varies by the type of prefix" would indicate that the actual identifier
used for even the same advertising router will be different for the
different type of prefix being advertised, which doesn't seem to be what
the subsequent discussion describes.)

   address for the router.  The IPv4/IPv6 Router Address as defined in
   [RFC3630] and [RFC5329] for OSPFv2 and OSPFv3 respectively provide an
   address to reach that router.

(nit) Is it useful to indicate that these are TLVs, here?

   the core OSPF route computation functionality.  They provide useful
   information for topology analysis and traffic engineering, especially
   on a controller when this information is advertised as an attribute
   of the prefixes via mechanisms such as Border Gateway Protocol Link-
   State (BGP-LS) [RFC7752] [I-D.ietf-idr-bgp-ls-segment-routing-ext].

The draft-ietf-idr-bgp-ls-segment-routing-ext reference seems rather
unmotivated by the current prose leading up to it.  Per John's Discuss
some further exposition on the expected use case might help.