Re: [IPv6] Removing extension headers from packets (revisited)

[Mark Smith <[e-mail]>]

Hi Brian,

On Tue, 15 Aug 2023 at 12:04, Brian E Carpenter
<[e-mail]> wrote:
>

<snip>

>
> Hang on. If my initial packet is (simplified):
>
> SAx|DAy|EHz|payload
>
> (where SAx and DAy are the specific source and destination GUAs)
>
> and an egress router wraps it up as
>
> SAx|DAy|(SAx|DAy|EHz|payload)
>
> i.e. the packet was encapsulated with protocol 41 *using the same addresses* but no EH's, and later the ingress router that owns the prefix of DAy unwraps it as:
>
> SAx|DAy|EHz|payload
>
> again, it seems to me that the process can be fast and simple, and the packet on the open Internet has no EH and therefore no problem. No tunnel set-up needed, as long as everyone lets protocol 41 through.
>

The drawback of duplicate SA/DA is that a receiving router needs to
inspect literally every packet it receives beyond the fixed IPv6
header, looking for the special handling EH. (Side note: Duplicate
SA/DA was also proposed in draft-ietf-ippm-ioam-ipv6-options for
IOAM).


If special handling could be encoded in the outer packet's DA, they
could then easily be identified for special handling using a /128
route in the FIB.

Other packets without the special handling DA are forwarded normally,
without looking for the EH.


An address like this already exists:

fe80::0/128 - the link-local subnet router anycast address


The packet sent by the host would look like this (H.<address type>
meaning host address of <type>):

(Outer:)[SA:H.LLA|DA:fe80::0|Special Handling EH]
(Inner:)[SA:H.LLA/ULA/GUA|DA:<blah>|payload for <blah> DA to process]


1. The first hop router would receive the packet, FIB match on DA fe80::0/128.

2. It would remove the outer IPv6 header, and then perform the
processing according to [Special Handling EH].

3. Post-processing, the decapsulated packet is then sent back into the
forwarding plane or forwarding domain as
[SA:H.ULA/GUA|DA:<blah>][payload for DA to process] for further
forwarding.


Encoding of special handling in DAs is not new, emergency telephone
numbers (000/911/112) are also examples, as are anycast pizza chain
local shop instance phone numbers.

Regards,
Mark.