Re: IPv6 header insertion in a controlled domain

[Gyan Mishra <[e-mail]>]

I would like to make a point which I tried to do earlier on this thread
that with SRv6 any flow entering the domain from an external CE device is
“encapsulated” upon entering the domain as an overlay BGP service instance
and then in the underlay is hop by hop routed based on explicit segment
list from SRH header inserted on the ingress PE node of the SR domain.

What I am trying to say is that we had asked Spring to do encapsulation
since in flight eh insertion violated 8200 IP6 spec.  It appears the fact
is that encapsulation is part of the SRv6 spec for flow entering the SR
domain from a customer CE external device.

So now if we have Spring do another encapsulation it would be a double
encapsulation.

In another thread with Adrian I have asked a detailed questions related to
the the TI-LFA 2nd EH header which I believe TI-LFA behavior is similar to
MPLS ldp remote LFA when with MPLS a label is added at the PLR junction
point.  So with TI-LFA I believe an encapsulation has to happen for that to
work and must already be in the specification.  I am still researching to
find the spec where that is stated.


So in a nutshell it is very possible we maybe good to go and SRv6 is
abiding by the IPv6 rules with eh insertion.

See draft below.

https://tools.ietf.org/html/draft-ietf-6man-segment-routing-header-26
<https://tools.ietf.org/html/draft-ietf-6man-segment-routing-header-26#section-3>

I had posted a draft from BESS WG that mentions the encapsulation as part
of the SRv6 spec.

So it does appear that SRv6 is following adherence to IPV6 specification.


3
<https://tools.ietf.org/html/draft-ietf-6man-segment-routing-header-26#section-3>.
SR Nodes

   There are different types of nodes that may be involved in segment
   routing networks: source SR nodes originate packets with a segment in
   the destination address of the IPv6 header, transit nodes that
   forward packets destined to a remote segment, and SR segment endpoint
   nodes that process a local segment in the destination address of an
   IPv6 header.
3.1 <https://tools.ietf.org/html/draft-ietf-6man-segment-routing-header-26#section-3.1>.
Source SR Node

   A Source SR Node is any node that originates an IPv6 packet with a
   segment (i.e.  SRv6 SID) in the destination address of the IPv6
   header.  The packet leaving the source SR Node may or may not contain
   an SRH.  This includes either:

      A host originating an IPv6 packet.

      An SR domain ingress router encapsulating a received packet in an
      outer IPv6 header, followed by an optional SRH.

   The mechanism through which a segment in the destination address of
   the IPv6 header and the Segment List in the SRH, is derived is
   outside the scope of this document.
3.2 <https://tools.ietf.org/html/draft-ietf-6man-segment-routing-header-26#section-3.2>.
Transit Node

   A transit node is any node forwarding an IPv6 packet where the
   destination address of that packet is not locally configured as a
   segment nor a local interface.  A transit node is not required to be
   capable of processing a segment nor SRH.
3.3 <https://tools.ietf.org/html/draft-ietf-6man-segment-routing-header-26#section-3.3>.
SR Segment Endpoint Node

   A SR segment endpoint node is any node receiving an IPv6 packet where
   the destination address of that packet is locally configured as a
   segment or local interface.



On Mon, Dec 9, 2019 at 4:45 PM Fernando Gont <[e-mail]> wrote:

> On 8/12/19 14:19, [e-mail] wrote:
> > Tom,
> >
> >> IMO, even before we ask the of how to make header insertion work, we
> >> need to ask and get answers to the question why it's needed. That's
> >> why I created the thread on necessity (please comment on it). Until
> >> there is a clear justification for this mechanism, I personally don't
> >> see why the WGshould spend time trying to "make it work".
> >
> > I started this thread to see if there was agreement that the mechanism
> _could_ be made to work in the most simple topology.
> > I don't think "why" is required to have that discussion.
>
> Well, you are going against the way I've seen IETF wg operate --
> including 6man.
>
> Every time I've seen anybody propose something, there was something to
> be achieved, and there was an argument why a particular solution had
> been selected and was being evaluated.
>
> But, if we are at it: I want one solution that stuffed three SRHs, and
> two DOHs. Will we evaluate that one, too? -- If you wonder why such
> strange thing: I won't answer why, either.
>
> Any proposal for EH insertion should explain why they need it, and why
> the most obvious, and compliant, encapsulation doesn't work for solving
> the problem.
>
> Thanks,
> --
> Fernando Gont
> SI6 Networks
> e-mail: [e-mail]
> PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492
>
>
>
>
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-- 

Gyan S. Mishra

IT Network Engineering & Technology

Verizon Communications Inc. (VZ)

13101 Columbia Pike FDC1 3rd Floor

Silver Spring, MD 20904

United States

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Email: [e-mail]

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