Re: [Pals] [Int-area] L2TP sequencing: Commonly disabled for IP data? Or always?

Stewart Bryant <stewart.bryant@gmail.com> Fri, 04 June 2021 15:07 UTC

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From: Stewart Bryant <stewart.bryant@gmail.com>
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Date: Fri, 4 Jun 2021 16:07:10 +0100
In-Reply-To: <5c60cc79-1552-3f52-641f-e508780227ae@bobbriscoe.net>
Cc: Stewart Bryant <stewart.bryant@gmail.com>, intarea IETF list <int-area@ietf.org>, "Carlos Pignataro (cpignata)" <cpignata@cisco.com>, Ignacio Goyret <ignacio.goyret@nokia.com>
To: Bob Briscoe <ietf@bobbriscoe.net>, pals@ietf.org
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Subject: Re: [Pals] [Int-area] L2TP sequencing: Commonly disabled for IP data? Or always?
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Adding PALS and someone there may know.

Stewart



> On 4 Jun 2021, at 15:13, Bob Briscoe <ietf@bobbriscoe.net> wrote:
> 
> Int-area list,
> 
> I'm looking for experience on common L2TP practice, most likely from operators. I tried sending this query to the L2tpext@ietf.org <mailto:L2tpext@ietf.org> list, as advised by Carlos Pignataro, but apparently it no longer exists. So I think int-area is the "list of last resort" for this.
> 
> The L2TP RFC says sequencing /can/ be disabled for IP data, but it doesn't say SHOULD or MUST. Is it possible that some operators enable L2TP sequencing for IP data? And if so, do you know why they would? Also, are you aware of any other types of tunnel that might try to keep IP data packets in sequence?
> 
> My reason for asking: 
> We (in tsvwg) are working on active queue management technology. Certain AQM schemes (e.g. FQ-CoDel, L4S) give lower delay to a subset of traffic. If the bottleneck queue supports such an AQM and it is within an L2TP tunnel with sequencing enabled, the egress would hold back all the nice low delay packets until it can put them back into order with the higher delay traffic.
> 
> We intend to advise that operators MUST disable L2TP sequencing if they wish to deploy these AQMs within an L2TP tunnel. So we need to know:
> Whether this will create a dilemma for any operators who need L2TP sequencing of IP data for some reason;
> Or whether we even need to bother giving the advice, because no operator would ever enable L2TP sequencing of IP data anyway.
> 
> Obviously, some operators already use existing technologies like Diffserv to reduce delay for a subset of IP data traffic, so I assume they always disable L2TP sequencing anyway. 
> 
> Regards
> 
> 
> Bob Briscoe
> 
> 
> -- 
> ________________________________________________________________
> Bob Briscoe                               http://bobbriscoe.net/ <http://bobbriscoe.net/>_______________________________________________
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