Re: [v6ops] draft-cc-v6ops-wlcg-flow-label-marking-00.txt

Hi Dale,

Thanks for documenting this.

As well as the impact on ECMP/LAG (where you might add a reference to
RFC 6438), could you also mention the impact on server load balancing
(RFC 7098)? The real issue here is that with only 5 random bits, the
probability of two very large flows hashing to the same path or server
is higher than we'd like. But since the WLCG flows are *all* very large,
this presumably doesn't matter so much in your use case?

I'd never thought about using a Hamming code to generate flow labels.
But since a given flow must use the same flow label throughout, you can
only use the regular 5-tuple as input to the Hamming code. I don't
believe that a Hamming code will give you a discrete uniform distribution,
but I'm not an expert in that area. An expert known as ChatGPT says:
"No, a Hamming code does not produce a discrete uniform distribution...
The non-uniformity of the distribution arises from the fact that Hamming
codes prioritize error detection and correction capabilities over
uniformity of codeword distribution."

So I think that simply using a stateless hash is the best way. These
days I like FNV (draft-eastlake-fnv) which is easy and cheap to implement.

Regards
    Brian Carpenter

On 30-Jun-23 07:52, Dale W. Carder wrote:
> Hi folks,
> 
> We have submitted this draft documenting our experimental use of the
> IPv6 flow label for packet marking and the considerations we had made
> along the way that sort of got us to this point.
> 
> I'm hoping we could get some initial discussion underway here before
> IETF 117.  Thanks!
> 
> Dale
> 
> ----- Forwarded message from internet-drafts@ietf.org -----
>> Date: Thu, 29 Jun 2023 12:18:53 -0700
>> From: internet-drafts@ietf.org
>> Subject: New Version Notification for draft-cc-v6ops-wlcg-flow-label-marking-00.txt
>>
>>
>> A new version of I-D, draft-cc-v6ops-wlcg-flow-label-marking-00.txt
>> has been successfully submitted by Dale W. Carder and posted to the
>> IETF repository.
>>
>> Name:		draft-cc-v6ops-wlcg-flow-label-marking
>> Revision:	00
>> Title:		Use of the IPv6 Flow Label for WLCG Packet Marking
>> Document date:	2023-06-29
>> Group:		Individual Submission
>> Pages:		15
>> URL:            https://www.ietf.org/archive/id/draft-cc-v6ops-wlcg-flow-label-marking-00.txt
>> Status:         https://datatracker.ietf.org/doc/draft-cc-v6ops-wlcg-flow-label-marking/
>> Html:           https://www.ietf.org/archive/id/draft-cc-v6ops-wlcg-flow-label-marking-00.html
>> Htmlized:       https://datatracker.ietf.org/doc/html/draft-cc-v6ops-wlcg-flow-label-marking
>>
>>
>> Abstract:
>>     This document describes an experimentally deployed approach currently
>>     used within the Worldwide Large Hadron Collider Computing Grid (WLCG)
>>     to mark packets with their project (experiment) and application.  The
>>     marking uses the 20-bit IPv6 Flow Label in each packet, with 15 bits
>>     used for semantics and 5 bits for entropy.  Alternatives, in
>>     particular use of IPv6 Extension Headers (EH), were considered but
>>     found to not be practical.  The WLCG is one of the largest worldwide
>>     research communities and has adopted IPv6 heavily for movement of
>>     many tens of PB of data annually, with the ultimate goal of running
>>     IPv6 only.
>>
>>                                                                                    
>>
>>
>> The IETF Secretariat
>>
>>
> 
> ----- End forwarded message -----
> 
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