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

[Brian E Carpenter <[e-mail]>]

On 15-Aug-23 17:26, Mark Smith wrote:
> 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).

Yes, after it's unwrapped it. That's the price of being a border
node on a limited domain. There is no free lunch here (see my
points about service level agreements sent a minute or two ago).

     Brian

> 
> 
> 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.
> .