Re: [lisp] [spring] IPv6-compressed-routing-header-crh

[Mark Smith <[e-mail]>]

Hi Robert,

Sorry not to get back to you sooner.

On Mon, 1 Apr 2019 at 01:40, Robert Raszuk <[e-mail]> wrote:
>
> Hi Mark,
>
<snip>
>
> Since you correctly observed that now SID can be 32 bit and that is similar to the size of IPv4 my fundamental question is why not use something which already exists instead of defining some sort of new  from scratch ?
>
> It will be perfectly fine to have full proper SRv6 with SRH and LISP or Vector Routing as an alternative options. I really do not see a room or need for yet one more mapping plane. What problem does it solve which would not be already solved elsewhere ?
>

Well, there seems to be or have been concerns about the overhead of
using 128 bit SIDs in IPv6. That seemed to be the motivation for EH
insertion.

I sympathise with the overhead concern, although I'd be quite happy to
put up with the overhead and bandwidth costs of full IPv6-in-IPv6
tunnelling in comparison to non-commodity operations like inserting
the SRH EH into existing IPv6 packets to avoid that overhead.
Bandwidth is always getting cheaper.

I think the value in using IPv6 as the transport for SR is that IPv6
is becoming and will be the future the commodity layer 3 protocol.
MPLS may be fairly commodity, however IPv6 will be more so, and I
think the reason is that it is an end-to-end protocol that hosts use
(I think this is also why Ethernet has become the dominant link-layer
protocol, even for WAN links).

So if SR wants to benefit from and leverage IPv6's commodification,
then it needs to be limited to commodity IPv6 operations. If it
deviates, then it isn't commodity IPv6 any more.

So my motivation for suggesting 32 bit SIDs in IPv6, and I'm guessing
Ron's too for his smaller variable SIDs proposal including 32 bits, is
to try to reduce the overhead of SR over IPv6, while also retaining
commodity IPv6 operation.

Regards,
Mark.