Re: 6man w.g. last call for <draft-ietf-6man-segment-routing-header-11.txt>

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

On 09/04/2018 20:09, stefano previdi wrote:
...
>> By contrast, draft-ietf-6man-segment-routing header defines the Segments Left as follows:
>>
>> "Defined in [RFC8200], it contains the index, in the Segment List, of the next segment to inspect.  Segments Left  is decremented at each segment.

Maybe you should say:
 Segments Left is decremented at each segment after processing the segment list and
 before forwarding the packet.

>> Therefore, if a packet arrives at a node and the following conditions are true, the node processes Segment[0]:
>>
>> - The packets IPv6 Destination address is local to the node
>> - The packet contains a Routing Extension Header
>> - The SL value in the Routing Extension Header is equal to 0
> 
> 
> SL==0 doesn’t imply any processing of the SRH. Both END and END.x functions starts with “IF SegmentsLeft > 0”.

IMHO that needs to be stated normatively in the spec, even if it seems obvious.
The section you are referring to only says:
"In this section we review two functions that may be associated to a segment:"
and cites an informational reference (draft-ietf-spring-segment-routing).
So the junior programmer asked to actually write some network processor code
doesn't know that she MUST NOT process the SRH, because it's only a lower
case "may".

   Brian