Re: Flow label [not draft-han-6man-in-band-signaling-for-transport-qos-00.txt]

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

On 21/10/2017 09:53, Tom Herbert wrote:
> On Fri, Oct 20, 2017 at 12:06 PM, Leddy, John <[e-mail]>
> wrote:
> 
>> In order packet delivery requirements considered harmful to the Internet…
>>
>>
>>
>> I’m assuming random per packet flow label assignments are within spec as
>> long as they are set by the source.
>>
>>
>>
> 
> Yes, there is no requirement that the flow label be persistent at all in a
> flow. 

http://mailman.postel.org/mailman/listinfo/internet-history says:

   To enable Flow-Label-based classification, source nodes SHOULD assign
   each unrelated transport connection and application data stream to a
   new flow.  A typical definition of a flow for this purpose is any set
   of packets carrying the same 5-tuple {dest addr, source addr,
   protocol, dest port, source port}.  It should be noted that a source
   node always has convenient and efficient access to this 5-tuple,
   which is not always the case for nodes that subsequently forward the
   packet.

So, technically it's a recommendation, not a requirement. But for load
balancing or ECMP to actually work, it's a requirement.

> That gives some nice properties. For instance, at FB we implemented
> flowbender using the flow label so that when a host detects a poor quality
> path it can randomly try another flow label for the connection to hopefully
> find a better path (a type of source routing). Random Packet Spraying could
> use the flow label and randomly set it per packet to achieve perfect load
> balancing in a multi-path network.

I think the MPTCP people might have a word or two to say about that.

   Brian