Re: [bess] Alvaro Retana's Discuss on draft-ietf-bess-mvpn-fast-failover-13: (with DISCUSS and COMMENT)

[Greg Mirsky <[e-mail]>]

Hi Alvaro,
I much appreciate your quick response and the clarifying questions. Please
find my answers in-lined under GIM>> tag.
I will upload the document with the additional updates from my answers.

Regards,
Greg

On Thu, Jan 21, 2021 at 8:51 AM Alvaro Retana <[e-mail]>
wrote:

> Greg:
>
> Hi!
>
> I trust that the changes we’ve discussed are reflected in the diffs.
>
> About the new text below….   It looks ok to me.  Just a couple of
> questions:  When is this new TLV considered malformed?
>
GIM>>  I've added text to the description of the Length field:
   o  The Length field is 4 for the IPv4 address family and 16 for the
      IPv6 address family.  The TLV is considered malformed if the field
      is set to any other value.

>   Given that it is required for p2mp, what action should the receiver make
> if it is not included?
>
  I’m ok with the action being Attribute Discard; I just want that to be
> explicit.
>
GIM>> You're right, making it explicit with:
   The BFD Discriminator attribute
   that does not include the Source IP Address TLV MUST be handled
   according to the "attribute discard" approach, as defined in
   [RFC7606].
>
>
> I’ll clear my DISCUSS when the update is posted.
>
> Thanks!
>
> Alvaro.
>
> On January 21, 2021 at 10:59:41 AM, Greg Mirsky ([e-mail])
> wrote:
>
> Hi Alvaro,
> after the discussion with our AD and Chairs, we have prepared an update
> with a new Source IP Address TLV. The Source IP Address TLV is required in
> the BFD Discriminator attribute is the BFD Mode is set to P2MP value. Below
> is the updated text.
>
>    - In Section 3.1.6:
>
>    An optional Source IP Address TLV is defined in this document.  The
>    Source IP Address TLV MUST be used when the value of the BFD Mode
>    field's value is P2MP BFD Session.  For the Source IP Address TLV
>    fields are set as follows:
>
>    o  The Type field is set to 1 Section 7.3.
>
>    o  The Length field is 4 for the IPv4 address family and 16 for the
>       IPv6 address family.
>
>    o  The Value field contains the address associated with the
>       MultipointHead of the P2MP BFD session.
>
>    The BFD Discriminator attribute MUST be considered malformed if its
>    length is smaller than 11 octets or if Optional TLVs are present, but
>    not well-formed.  If the attribute is deemed to be malformed, the
>    UPDATE message SHALL be handled using the approach of Attribute
>    Discard per [RFC7606].
>
>
>    - In Section 3.1.6.1
>
>    o  MUST use the IP address included in the Source IP Address TLV of
>       the BFD Discriminator attribute as the source IP address when
>       transmitting BFD Control packets;
>
>
>    - In section 3.1.6.2
>
>          the IP address in the Source IP Address TLV included the BFD
>          Discriminator attribute in the x-PMSI A-D Route;
>
>
> Also, all updates resulting from our discussion are highlighted in the
> attached diff file. Please let me know if this update addresses your
> comment on the origin of the PE address used in the P2MP BFD session. I
> much appreciate your review, comments, and suggestions.
>
> Best regards,
> Greg
>
> On Wed, Dec 23, 2020 at 12:36 PM Alvaro Retana <[e-mail]>
> wrote:
>
>> On December 23, 2020 at 1:51:13 PM, Greg Mirsky wrote:
>>
>>
>> Greg:
>>
>> I have just one reply.  I am also leaving in the text where we're
>> waiting for Chair/AD input.
>>
>>
>> Thanks!!
>>
>> Alvaro.
>>
>>
>> ...
>> > > > Method described in Section 3.1.2 monitors the state of the data
>> > > > plane but only for an egress P-PE link of a P-tunnel. As a result,
>> > > > network failures that affect upstream links might not be detected
>> > > > using this method and the MVPN convergence would be determined by
>> the
>> > > > convergence of the BGP control plane.
>> > >
>> > > "...would be determined by the convergence of the BGP control plane."
>> > >
>> > > This is a case where it seems that combining §3.1.1/§3.1.2 would make
>> > > sense. In fact, tracking the state of the root seems helpful in other
>> > > cases too (below) that are looking at different things. You said
>> > > before that you didn't think combining the methods make sense -- can
>> > > you please explain why in this section?
>> >
>> > GIM3>> But that would be my personal opinion that the WG might not
>> agree.
>> > I'm always glad to discuss technical ideas, pros, and contras of that or
>> > this approach to solve the problem but I feel uneasy adding my personal
>> > opinions in the WG document. The document lists a set of techniques but
>> how
>> > they are combined in a product is left for product managers and
>> developers
>> > to decide.
>> > Would you agree?
>>
>> The document already talks about combinations, specifically with root
>> tracking.
>>
>> The text above already mentions "convergence of the BGP control
>> plane", which I think makes direct reference to root tracking.  §3.1.3
>> and §3.1.4 both say that "the downstream PE can immediately update its
>> UMH when the reachability condition changes" -- this is the exact same
>> text used in §3.1.1 to describe root tracking.
>>
>> The opinion of not combining is already not represented in the text,
>> and there is direct reference to using an additional method.  If you
>> didn't mean to use the same text to refer to different things then
>> perhaps some clarification would be in order.
>>
>>
>>
>>
>> ...
>> > > > > > > (2b) ...
>> > > > > > >
>> > > > > BTW, I agree with Jeff in > that bfd/idr should be given the
>> opportunity
>> > > > > to review this document.
>> > > >
>> > > > GIM2>> I'm leaving this decision to the AD and Chairs of BESS and
>> BFD WGs.
>> > >
>> > > Yup.
>>
>> ...
>> > > > > > > (18) §3.1.6.2(http://3.1.6.2): If the IP address doesn't map
>> > > > > > > correctly at the downstream PE (for example, a different local
>> > > > > > > address is used that doesn't correspond to the information in
>> the
>> > > > > > > PMSI attribute), what action should it take? Can the tunnel
>> still
>> > > > > > > be monitored?
>> > > > > >
>> > > > > > GIM>> There's a possibility that the same downstream PE is
>> monitoring
>> > > > > > more than one P-tunnel. Since each Upstream PE assigns its own
>> BFD
>> > > > > > Discriminator, there's a chance that the same value is picked
>> by more
>> > > > > > than one Upstream PE.
>> > > > > > According to Section 5.7 of the RFC 8562:
>> > > > > > IP and MPLS multipoint tails MUST demultiplex BFD packets based
>> on a
>> > > > > > combination of the source address, My Discriminator, and the
>> identity
>> > > > > > of the multipoint path that the multipoint BFD Control packet
>> was
>> > > > > > received from. Together they uniquely identify the head of the
>> > > > > > multipoint path.
>> > > > > >
>> > > > > > We may consider adding the source address in the BFD
>> Discriminator
>> > > > > > attribute as an optional TLV. I think that might be a good
>> extension
>> > > > > > that can be introduced in a new document.
>> > > > >
>> > > > > Why wait for a new document? You made a pretty good case for
>> > > > > signaling the source address.
>> > > >
>> > > > GIM2>> I'd like to defer this question to our AD and BESS WG Chairs.
>> > >
>> > > Again, you made a good case for why it is needed for the mechanism to
>> > > work. Leaving it for later might just leave a hole. Sure, let's hear
>> > > from the Chairs/AD.
>>
>