[Idr] John Scudder's No Objection on draft-ietf-idr-bgp-flowspec-oid-13: (with COMMENT)

John Scudder via Datatracker <noreply@ietf.org> Fri, 07 May 2021 19:57 UTC

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Subject: [Idr] John Scudder's No Objection on draft-ietf-idr-bgp-flowspec-oid-13: (with COMMENT)
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John Scudder has entered the following ballot position for
draft-ietf-idr-bgp-flowspec-oid-13: No Objection

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Thanks for this document, I'm glad to see it finally close to publication. I
have a few comments I hope will help improve it, below.

1. Section 2

   [RFC8955] defines a BGP NLRI [RFC4271] that can be used to distribute

RFC 4271 is the right citation for “BGP” but for “BGP NLRI” other than IPv4
unicast you want RFC 4760.

   the Flow Specification.  The aim is making sure that only speakers on

making -> to make

   originated in any location within the same autonomous system than the

than -> as

   Flow Specification received from an iBGP peer, it could be possible
   to disseminate such Flow Specification NLRIs directly from the

“It could be possible”? Or “it would be necessary”?

   validated when received by RR and R1.  Sometimes the Flow
   Specification needs to be originated on AS1.  ASBR1 could originate

on -> within

2. Section 4.1

          1.  This condition SHOULD be enabled by default (it may be
              disabled by explicit configuration as described on the
              next list item (b.2.1))..  an empty AS_PATH.

Looks as though “an empty AS_PATH” is a cut-n-paste error that should be

          3.  As an extension to this rule, a given non-empty AS_PATHs

AS_PATHs -> AS_PATH (agreement in number)

              AS_CONFED_SET segments), MAY be validated by policy.  A

I think “permitted” would be clearer than “validated”.

      Also, policy may be useful to validate a specific set of non-empty
      AS_PATHs (b.2.3).  For example, it could validate a Flow
      Specification whose AS_PATH contains only an AS_SEQUENCE with ASes
      that are all known to belong to the same administrative domain.

Same point, I suggest “permit”.

3. Section 4.2

   This rule prevents the exchange of BGP Flow Specification NLRIs at
   Internet exchanges with BGP route servers [RFC7947].

Since it may not be common knowledge that route servers don’t insert their own
AS number, I suggest a change something like this, for clarity:

   This rule prevents the exchange of BGP Flow Specification NLRIs at
   Internet exchanges with BGP route servers, which by design don’t insert
   their own AS number into the AS_PATH  ([RFC7947] Section

4. Section 4.2

      For clarity, the AS in the left-most position of the AS_PATH means
      the AS that was last added to the AS_SEQUENCE.

I suggest changing “last” to “most recently”. This is just personal preference,
though. I also suggest changing “AS_SEQUENCE” somehow, probably to “AS_PATH”.
The reason for this is there could be more than one AS_SEQUENCE in the AS_PATH
so the definite article isn’t quite correct. There is however only one AS_PATH,
and you can make the change without loss of generality or correctness. So, the
full suggested rewrite is:

      For clarity, the AS in the left-most position of the AS_PATH means
      the AS that was most recently added to the AS_PATH.

5. Section 4.2

      Specifications.  This is a security BGP threat, but out of the

“Security BGP threat” -> “security threat” (or “BGP security threat” if you

6. Section 4.2

      Using the new rule to validate a Flow Specification route received
      from an External Border Gateway Protocol (eBGP) peer belonging to
      the same local domain (in the case of a confederation) is out of
      the scope of this document.  Note that although it's possible, its
      utility is dubious.  Although it is conceivable that an router in
      the same local domain (both iBGP and eBGP within the same local
      domain) could send a rogue update, only eBGP (outside the local
      domain) risk is considered within this document (in the same
      spirit of the mentioned beforehand AS_PATH validation in

I’m having a hard time understanding this paragraph. This is at least partly
due to the use of “local domain“, which isn’t a well-defined term of art. You
could try something like “under the same administration“? But, even if I make
that change in my head as I read the paragraph, I still don’t get your point.

Is the whole paragraph strictly about confederations, and what you’re talking
about is a BGP session between a router in one member-AS and a router in
another member-AS of the confederation? If that’s it, I can probably propose
some new text.

Also, “an router” -> “a router”.

Also, you should cite RFC 5065 when you mention confederations.

7. Section 5

   its best-match unicast route) are learned from the same peer accross

accross-> across

8. Section 5

      Consider the validation procedure preceding this document.  The

I think what you mean here is “consider the validation procedure defined in RFC
8955“. If that’s correct, I suggest saying it that way. (If that’s not correct,
what did you mean?)

9. Section 7

   thus maintain security characteristics equivalent to the existing

Maintain -> maintains

10. Section 7

   The original AS_PATH validation rule ([RFC4271] section 6.3) becomes
   hereby optional (section 4.2).

I don’t think you’re actually updating RFC 4271, are you? The way you’ve
written this makes it sound as though you are. You’re relaxing the rule in RFC
8955, but as you point out in section 4.2, RFC 4271 makes AS_PATH neighbor AS
insertion enforcement optional to begin with:

   If the UPDATE message is received from an external peer, the local
   system MAY check whether the leftmost (with respect to the position
   of octets in the protocol message) AS in the AS_PATH attribute is
   equal to the autonomous system number of the peer that sent the
   message.  If the check determines this is not the case, the Error
   Subcode MUST be set to Malformed AS_PATH.

Maybe you could rewrite something like this: “As per section 4.2, it is becomes
optional to enforce that the AS_PATH attribute of a route received via the
External Border Gateway Protocol (eBGP) contains the neighboring AS in the
leftmost position of the AS_PATH attribute. Then we continue:

             If that original rule is actually not
   enforced it may introduce some security risks.  A peer (or a client
   of a route server peer) in AS X could advertise a rogue Flow
   Specification route whose first AS in AS_PATH was Y (assume Y is the
   first AS in the AS_PATH of the best-match unicast route).  This risk
   is impossible to prevent if the Flow Specification route is received
   from a route server peer.

I think you’ve missed out on the opportunity to point out that the risk can
also be mitigated if the route server itself enforces the optional rule of RFC
4271 section 6.3.. I think it’s fair to say that at an exchange point, the
administrator of the route server enjoys more trust then the administrators of
other routers at the exchange point.

               If that peer is known for a fact not to be
   a route server, that optional rule SHOULD be enforced for Flow
   Specification routes.

It may be necessary to say a little more about how you would get this knowledge
about the peer not being a route server. Possibly a rewrite could be something
like: "Unless configuration (or other means beyond the scope of this document)
indicates that the peer is a route server, that optional rule SHOULD be
enforced for Flow Specification routes from EBGP peers."

11. Section 7

   absolute and the new possibility than an iBGP speaker could send a

Than -> that