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

Any hash function must be close to "discrete uniform distribution"
Or else it would be a great help to crack it.
Ed/
-----Original Message-----
From: v6ops [mailto:v6ops-bounces@ietf.org] On Behalf Of Brian E Carpenter
Sent: Friday, June 30, 2023 1:50 AM
To: Dale W. Carder <dwcarder@es.net>; v6ops@ietf.org
Subject: 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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