Re: [Softwires] DS-Lite fragmentation RFC2473 reference

Daniel Roesen <dr@cluenet.de> Thu, 20 October 2011 07:42 UTC

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Date: Thu, 20 Oct 2011 09:42:31 +0200
From: Daniel Roesen <dr@cluenet.de>
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Subject: Re: [Softwires] DS-Lite fragmentation RFC2473 reference
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Hi Yiu,

On Thu, Oct 20, 2011 at 02:11:44AM +0000, Lee, Yiu wrote:
> Host behind B4 isn't aware he tunnel between B4 and AFTR. To make the host
> transparent to IPv4 fragmentation, we made the decision to mandate B4 (and
> AFTR) fragment and reassemble the oversized packet. We agree that there is
> a price to pay (i.e., CPU intensive operation in B4 and AFTR), but this
> should affect the host least.

Thanks for the clarification. Too bad the vendor landscape (both AFTR
and B4) grossly ignore that normative requirement of RFC6333 and either
fragment the payload instead of the tunnel, or - even worse - resort to
measures like issuing ICMPv4 "frag needed but DF set" even in response
to >1460 bytes IPv4 packets WITHOUT DF bit being set.

They all have significant problems with performance when being asked to
perform proper RFC6333 operation. And then speak of hardening AFTRs
against reassembly resources starvation attacks...

Best regards,
Daniel

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