Re: [bess] draft-ietf-bess-evpn-overlay-10 PMSI with Ingress Replication

[Thomas Morin <[e-mail]>]

Hi Don,

Fedyk, Don, 2017-12-15 15:34:
> I know I read this part several times.  The draft specifies a
> Multicast tunnel with attribute Ingress replication that you don't
> use for multicast traffic.
> 
> > > > > > 
> 
>    For example,
>    the PMSI Tunnel attribute may indicate the multicast tunnel is of
>    type PIM-SM; whereas, the BGP Encapsulation extended community may
>    indicate the encapsulation for that tunnel is of type VxLAN. The
>    following tunnel types as defined in [RFC6514] can be used in the
>    PMSI tunnel attribute for VXLAN/NVGRE:
> 
>          + 3 - PIM-SSM Tree
>          + 4 - PIM-SM Tree
>          + 5 - BIDIR-PIM Tree
>          + 6 - Ingress Replication
> 
> 
>    Except for Ingress Replication, this multicast tunnel is used by
> the
>    PE originating the route for sending multicast traffic to other
> PEs,
>    and is used by PEs that receive this route for receiving the
> traffic
>    originated by hosts connected to the PE that originated the route.
> <<<<<

Honestly, interpreting the above as "The draft specifies a Multicast
tunnel with attribute Ingress replication that you don't use for
multicast traffic" is in my opinion really far fetched, for two
reasons:
- the paragraph does not talk about the advertised routes, but what is
used in the dataplane (the actual dataplane construct corresponding to
the PMSI Tunnel Attribute)
- the paragraph only talks about the traffic flowing from advertiser to
remote PEs, so it does not exclude the other direction of traffic from
being used in the case of ingress replication

So well, it's not the first time that additional text aiming at helping
people understand, rather than add precisions required for interop,
ends up being a source of questions.

Here I would suggest to authors to consider purely removing this
paragraph, not because it would be wrong or ambiguous (as said above, I
don't think it is), but because as far as I can tell it has never meant
to specify anything not already implied by RFC7432, but was here only
to help understand.

Best,

-Thomas




-----Original Message-----
> From: John E Drake [mailto:[e-mail]] 
> Sent: Friday, December 15, 2017 9:52 AM
> To: EXT - [e-mail] <[e-mail]>; Fedyk,
> Don <[e-mail]>; Marco Marzetti <[e-mail]>
> Cc: [e-mail]
> Subject: RE: [bess] draft-ietf-bess-evpn-overlay-10 PMSI with Ingress
> Replication
> 
> Thomas,
> 
> I completely agree w/ your email, below.
> 
> Yours Irrespectively,
> 
> John
> 
> 
> > -----Original Message-----
> > From: BESS [mailto:[e-mail]] On Behalf Of Thomas Morin
> > Sent: Friday, December 15, 2017 5:42 AM
> > To: Fedyk, Don <[e-mail]>; Marco Marzetti <marco@lamehost.
> > it>
> > Cc: [e-mail]
> > Subject: Re: [bess] draft-ietf-bess-evpn-overlay-10 PMSI with
> > Ingress 
> > Replication
> > 
> > Hi Don,
> > 
> > Fedyk, Don, 2017-12-14 20:33:
> > > I think the gray area is that this draft talks about BUM traffic
> > > and 
> > > ingress replication and then has a section on Multicast tunnels 
> > > which excludes ingress replication traffic from the tunnels.
> > 
> > No, ingress replication is not excluded at all:
> > 
> >    The following tunnel types as defined in [RFC6514] can be used
> > in
> >    the PMSI tunnel attribute for VXLAN/NVGRE:
> > 
> >          + 3 - PIM-SSM Tree
> >          + 4 - PIM-SM Tree
> >          + 5 - BIDIR-PIM Tree
> >          + 6 - Ingress Replication
> > 
> > > If you are using point to point VXLAN/NVGRE  tunnels then
> > > ingress 
> > > replication is default [...]
> > 
> > This formulation surprises me: that some implementations behave as
> > you 
> > describe is possibly true (this seems to be the case of the 
> > implementation that triggered this discussion), but I don't know
> > about 
> > any text in the specs we are discussing that would imply such a
> > 'default'.
> > 
> > You might have implementations that in the absence of any local 
> > configuration for an EVPN instance on which type of tunnel to use
> > for 
> > BUM, will default to ingress replication: this is fine, out of the 
> > scope of what is specified for interop, and not breaking other 
> > implementations (as long, of course, that what is chosen locally
> > is 
> > then advertised as expected in a PMSI Tunnel Attribute).
> > 
> > 
> > > but IMET is being used to identify the NVE IP.    I read RFC7432
> > > and
> > > RFC6514 in this area and thought that the PMSI attribute MUST be
> > > set 
> > > when there is an Inclusive Multicast Ethernet tag IMET.
> > 
> > Yes!  (the text of RFC7432 quoted by Ali reminds us that)
> > 
> > 
> > > I can see two possible fixes:
> > > -          Specify that the PMSI attribute MUST be set if there
> > > is an
> > > IMET route and specify correct attribute.
> > 
> > Given the content of RFC7432 and the fact that this is a normative
> > ref 
> > of draft-ietf-bess-evpn-overlay, I think that we don't need to
> > repeat 
> > this MUST in draft-ietf-bess-evpn-overlay.  That is, unless we 
> > explicitly identify an ambiguous piece of text.
> > 
> > > -          Allow that ingress replication is default when PMSI is
> > > absent but accept PMSI that specifies ingress replication.
> > > 
> > 
> > I don't think we should do that. It would overnight make non-
> > compliant 
> > pre- standard implementation of draft-ietf-bess-evpn-overlay,
> > without 
> > a rationale to do so except coping with an implementation that
> > assumed a bit too much.
> > 
> > Best,
> > 
> > -Thomas
> > 
> > 
> > 
> > > From: BESS [mailto:[e-mail]] On Behalf Of Marco 
> > > Marzetti
> > > Sent: Thursday, December 14, 2017 9:21 AM
> > > To: Thomas Morin <[e-mail]>
> > > Cc: [e-mail]
> > > Subject: Re: [bess] draft-ietf-bess-evpn-overlay-10 PMSI with 
> > > Ingress Replication
> > > 
> > > Hello,
> > > 
> > > I have encountered an implementation that is not attaching any
> > > PMSI 
> > > to the IMET.
> > > The authors think they don't really need it because they only 
> > > support Ingress Replication.
> > > Such behavior breaks interoperability with other implementations 
> > > that are dropping the NLRI if PMSI is not attached.
> > > 
> > > So i looked at draft-ietf-bess-evpn-overlay-10 and noticed that 
> > > there's no clear indication of what the proper behavior is.
> > > As said i assumed i had to look at RFC7432 and RFC6514 (and i
> > > did 
> > > it), but i wasn't 100% sure and i preferred to ask.
> > > 
> > > Onestly you already made my day by confirming what i thought.
> > > My suggestion was to make things more clear, but i admit that it 
> > > could look redundant.
> > > 
> > > Thanks
> > > 
> > > 
> > > 
> > > 
> > > 
> > > 
> > > 
> > > On Thu, Dec 14, 2017 at 2:39 PM, Thomas Morin
> > 
> > <[e-mail]
> > > m> wrote:
> > > > Hi Marco,
> > > > 
> > > > Marco Marzetti, 2017-12-14 12:25:
> > > > > I am writing this email asking you to clarify what's the
> > > > 
> > > > suggested
> > > > > behavior when PMSI Tunnel Type is set to "Ingress
> > > > > Replication"
> > > > 
> > > > (type
> > > > > 6) as draft-ietf-bess-evpn-overlay-10 only suggests what to
> > > > > do
> > > > 
> > > > with
> > > > > multicast tunnel trees.
> > > > > 
> > > > > I think the originating PE should conform with RFC6514 and
> > > > 
> > > > RFC7432
> > > > > (from which you've taken inspiration) and always (RFC2119
> > > > > MUST) 
> > > > > attach PMSI Tunnel attribute with the Tunnel Type set to
> > > > > Ingress 
> > > > > Replication and Tunnel Identifier set to a routable address
> > > > > of
> > > > 
> > > > the PE
> > > > > itself (more specifically NVE's IP address).
> > > > > 
> > > > > Is that correct?
> > > > > In that case i suggest to add the following line at the end
> > > > > of 
> > > > > Section 9.
> > > > > """
> > > > > For Ingress Replication the PE should follow what's stated in
> > > > 
> > > > RFC6514
> > > > > Section 5 .
> > > > > """
> > > > 
> > > > The text of section 9 lists "Ingress Replication" in the list
> > > > of 
> > > > tunnel types that can be used. My understanding is that, in
> > > > the 
> > > > absence of anything being specifically said for Ingress 
> > > > Replication, an implementation should follow what is said in
> > > > RFC7432 and RFC6514.
> > > > (What
> > > > other specs could it follow to implement this supported type ?
> > > > RFC7432
> > > > and RFC6514 are more than an inspiration here, these are specs 
> > > > that the document refers to explicitly)
> > > > 
> > > > So I'm not sure that it is useful or needed to add text.
> > > > 
> > > > Can you perhaps expand on why the current text would possibly
> > > > be 
> > > > ambiguous, misleading or incomplete...?
> > > > 
> > > > -Thomas
> > > > 
> > > 
> > > 
> > > 
> > > --
> > > Marco
> > 
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