Re: [IPv6] Progress of comments resolution on draft-ietf-6man-enhanced-vpn-vtn-id

[[e-mail]]

Hi Jie, all,

I think we still need first a solid justification for per-NRP match behavior and also for differentiated match behavior for flows within an NRP. 

That's said, IMO most of the cases can be caught by fall back as default behavior + config to override the behavior with a drop when no match. Supplying a config to override the default behavior is a minor task compared to touching a node to provision VTN resource partitions, etc.

Cheers,
Med

> -----Message d'origine-----
> De : Dongjie (Jimmy) <[e-mail]>
> Envoyé : mardi 19 décembre 2023 03:57
> À : Ketan Talaulikar <[e-mail]>; Dongjie (Jimmy)
> <jie.dong=[e-mail]>
> Cc : BOUCADAIR Mohamed INNOV/NET <[e-mail]>;
> [e-mail]; 6man <[e-mail]>; draft-ietf-6man-
> [e-mail]
> Objet : RE: [IPv6] Progress of comments resolution on draft-ietf-
> 6man-enhanced-vpn-vtn-id
> 
> Hi Ketan,
> 
> Thanks for the comment. As you have corrected in another mail,
> this flag is not in the SRH.
> 
> I see you also agree that when the NRP ID in packet does not
> match with any NRP-ID available on the node, an indication to
> control whether to drop or fallback to best effort is needed.
> 
> If you read my below email carefully, such indication is not a
> simple global nob, it needs to be (at least) per-NRP, and
> actually it is for NRPs which are NOT provisioned on the local
> node/outgoing interface. This is different from what we usually
> do with configuration. Also note if using local configuration,
> this needs to be configured on every node along the path, not
> just the ingress node. This would further complicate the
> provisioning.
> 
> Thus it is considered more efficient to have the policy
> configured on the ingress node (which is be part of the NRP), and
> convey the indication to the downstream nodes together with the
> packet.
> 
> The existing TOS/DSCP/EXP are for QoS class indication, which are
> still useful within an NRP, so it is better not to overload them
> with additional semantics.
> 
> Best regards,
> Jie
> 
> > -----Original Message-----
> > From: Ketan Talaulikar [mailto:[e-mail]]
> > Sent: Tuesday, December 19, 2023 12:42 AM
> > To: Dongjie (Jimmy) <jie.dong=[e-mail]>
> > Cc: [e-mail]; [e-mail]; 6man
> > <[e-mail]>; [e-mail]
> > Subject: Re: [IPv6] Progress of comments resolution on
> > draft-ietf-6man-enhanced-vpn-vtn-id
> >
> > Hi Jie,
> >
> > I concur with Med on this one and don't see the need for the S-
> flag.
> > We've had TOS/DSCP/EXP for QoS where exactly the same scenario
> exists
> > and we've never had the need for such a flag/indication on the
> packet.
> >
> > This looks something like a local configuration/policy on the
> router
> > to me
> > - drop or fallback.
> >
> > We have very limited (8) flags on the SRH and there should be
> really
> > strong and compelling reasons for allocating one. This one
> doesn't look like such.
> >
> > Thanks,
> > Ketan
> >
> >
> > On Mon, Dec 18, 2023 at 9:17 PM Dongjie (Jimmy) <jie.dong=
> > [e-mail]> wrote:
> >
> > > Hi Med and Adrian,
> > >
> > > Thanks for the discussion. Here I'd like to give some further
> > > explanation about the usage of the S bit and why it is
> considered useful.
> > >
> > > In normal IPv6 packet forwarding, the next-hop and outgoing
> > > interface are determined based on longest matching of the
> destination IPv6 address.
> > > Packets with unmatched destination address are always
> dropped.
> > >
> > > After the introduction of the VTN (or NRP, will use VTN just
> in this
> > > mail) option, the next-hop and outgoing interface are still
> > > determined based on the destination address, this is
> unchanged.
> > >
> > > Then for packets whose next-hop and outgoing interface are
> > > determined, the VTN ID in the packet is used to match with
> the sets
> > > of local resources allocated to VTNs on the outgoing
> interface.
> > > There are two
> > possible results:
> > >
> > >   1) The VTN ID in the packet matches with the same VTN ID
> which is
> > > configured on the outgoing interface with a set of network
> > > resources, then the packet is forwarded using that set of
> resources.
> > >
> > >   2) The VTN ID in the packet does not match with any VTN ID
> > > configured on the outgoing interface. How should the node
> behave in
> > > this case? There are two options: 1) forward the packet with
> best
> > > effort. 2)
> > discard the packet.
> > >
> > > The S flag is used to tell the node how to forward the packet
> when
> > > the VTN-ID is not configured on the outgoing interface.
> > >
> > > With the above, I hope the functionality of the S flag is
> clear.
> > >
> > > Then the possible question is can this be achieved by
> configuration?
> > >
> > > The answer is it can, but possibly with a relatively higher
> cost.
> > > Note this is to control the behavior for NRPs which are not
> > > provisioned on the node's outgoing interface. Usually devices
> do not
> > > provide control configuration for elements which are not
> enabled.
> > > Even if such configuration is supported, as the behavior can
> be
> > > different per NRP, this requires lots of configuration for
> NRPs which are not enabled.
> > > Then we also need to consider the case where the behavior may
> be
> > > different for different flows under the same NRP...
> > >
> > > One analogy (not quite the same) to the S flag is the bits in
> IPv6
> > > extension header options which are used to control the
> forwarding
> > > behavior when the option cannot be parsed by some node. That
> may
> > > also be achieved via configuration on the nodes, while it
> turns out
> > > a better choice is to use flags to indicate the behavior for
> > > unrecognized
> > entities.
> > >
> > > With the above analysis, hope you also agree that the S flag
> is a
> > > more efficient approach for the required functionality.
> > >
> > > Best regards,
> > > Jie
> > >
> > > > -----Original Message-----
> > > > From: [e-mail]
> > <[e-mail]>
> > > > Sent: Thursday, December 14, 2023 8:23 PM
> > > > To: [e-mail]; Dongjie (Jimmy)
> <[e-mail]>
> > > > Cc: '6man' <[e-mail]>;
> > > > [e-mail]
> > > > Subject: RE: [IPv6] Progress of comments resolution on
> > > > draft-ietf-6man-enhanced-vpn-vtn-id
> > > >
> > > > Hi Adrian,
> > > >
> > > > > If the reason for splitting was technical or made for a
> radical
> > > > > improvement in readability, I might buy it. But I think
> it is
> > > > > purely a documentation issue.
> > > >
> > > > It isn't.
> > > >
> > > > The issue is that the use of the S bit is not justified,
> including
> > > > with
> > > the case you
> > > > mentioned below. This scan be handled by a local config
> parameter.
> > > > I
> > > fail to see
> > > > valid arguments so far why a per-NRP per-packet behavior
> will
> > > > needed to process a packet.
> > > >
> > > > Cheers,
> > > > Med
> > > >
> > > > > -----Message d'origine-----
> > > > > De : ipv6 <[e-mail]> De la part de Adrian
> Farrel Envoyé :
> > > > > mardi 12 décembre 2023 18:04 À : 'Dongjie (Jimmy)'
> > > > > <[e-mail]> Cc : '6man' <[e-mail]>;
> > > > > draft-ietf-6man-enhanced-vpn-vtn- [e-mail] Objet : Re:
> [IPv6]
> > > > > Progress of comments resolution on draft-ietf-
> > > > > 6man-enhanced-vpn-vtn-id
> > > > >
> > > > > Hi Jie,
> > > > >
> > > > > I rather expected some more comments on this, and I sat
> back to
> > > > > watch them, but then it went quiet and I forgot.
> > > > >
> > > > > So, "better late than never".
> > > > >
> > > > > As an aside, I wonder whether you should follow the
> advice given
> > > > > by TEAS in its work on draft-ietf-teas-enhanced-vpn, and
> feeding
> > > > > into IDR on draft-dong-idr-sr-policy-nrp. That is,
> generalise
> > > > > the VTN use case to NRP. I don't think this makes any
> technical
> > > > > change to the document, but makes the applicability wider
> (more
> > > > > generic) in step with what TEAS is doing. This seems to
> in
> > > > > keeping with the suggestions in your Section 5. But it
> would
> > > > > require some editorial work.
> > > > >
> > > > > I am not enthusiastic about splitting out multiple
> documents. It
> > > > > just makes more work.
> > > > >
> > > > > While I understand that the authors and Med thought this
> might
> > > > > be a compromise, I doubt that the authors really want to
> do this
> > > > > (that is, make more work for themselves) and since no one
> spoke
> > > > > up on the list, I wonder whether it the (perfectly valid)
> > > > > preference of only one person.
> > > > >
> > > > > If the reason for splitting was technical or made for a
> radical
> > > > > improvement in readability, I might buy it. But I think
> it is
> > > > > purely a documentation issue.
> > > > >
> > > > > It is worth noting that if the document was split then,
> without
> > > > > the S flag, the whole flags field would be unused in the
> > > > > remaining
> > document
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