Re: Other use cases for header insertion (was Re: Header Insertion and TI-FA)

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

On 12-May-20 02:48, Tom Herbert wrote:
> On Mon, May 11, 2020 at 5:58 AM Ron Bonica
> <rbonica=[e-mail]> wrote:
>>
>> Folks,
>>
>> Happy Monday!

This is confusing. For me, that was yesterday ;-)

>> As I was painting this weekend, I remembered that the use-case for IPv6 Header insertion is TI-LFA. This made the following questions come to mind:
>>
> 
> Ron,
> 
> There is at least one other use case for IPv6 Header insertion, that
> being IOAM. For example, an operator may wish to collect per packet
> statistics as packets traverse its network. An ingress router would
> insert headers containing IOAM, routers would annotate the
> information, and the egress router is expected to consume and remove
> the headers. The big difference between this use case and SR is that
> there's no source routing involved so the ingress router doesn't
> necessarily know what the egress router is, hence the ingress router
> wouldn't know the right destination address to use in encapsulation.
> 
> I believe that this is currently being developed and maybe even being
> deployed, but not under the auspices of IETF. Frankly, figuring out
> how to do header insertion in a sensible and standard way would be a
> step up from some of the methods being proposed. The most egregious
> proposal I've seen was one in which the ingress router would place the
> IOAM information in the TCP payload and then use diff serv bits to
> indicate the TCP payload is modified. Of course the day a network
> fails to remove the inserted information this completely breaks TCP!
> 
> This use case makes me think the WG should consider how to make header
> insertion safe and viable.

Unless I'm missing something, that would require a reworking of the last
sentence of this paragraph in RFC8200:

      o  The Upper-Layer Packet Length in the pseudo-header is the
         length of the upper-layer header and data (e.g., TCP header
         plus TCP data).  Some upper-layer protocols carry their own
         length information (e.g., the Length field in the UDP header);
         for such protocols, that is the length used in the pseudo-
         header.  Other protocols (such as TCP) do not carry their own
         length information, in which case the length used in the
         pseudo-header is the Payload Length from the IPv6 header, minus
         the length of any extension headers present between the IPv6
         header and the upper-layer header.

And some changes to the IPSec/AH rules about mutable fields, of course.

I'm not sure this is feasible without changing the IP version number.

    Brian