Re: [Int-area] WG Adoption Call: IP Fragmentation Considered Fragile

Toerless Eckert <tte@cs.fau.de> Sun, 26 August 2018 21:27 UTC

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Date: Sun, 26 Aug 2018 23:27:03 +0200
From: Toerless Eckert <tte@cs.fau.de>
To: Mikael Abrahamsson <swmike@swm.pp.se>
Cc: Tom Herbert <tom@herbertland.com>, int-area <int-area@ietf.org>, intarea-chairs@ietf.org
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Subject: Re: [Int-area] WG Adoption Call: IP Fragmentation Considered Fragile
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On Sat, Aug 25, 2018 at 08:32:41AM +0200, Mikael Abrahamsson wrote:
> > IMHO, we (network layer) should accept defeat on network layer
> > fragmentation and agree that we should make it easier for the
> > transport layer to resolve the problem.
> 
> I want to keep the fragmentation requirement for the network.

Why ? Whats the biggest benefit with IPv6 ?

Took us decades to figure out that in-network
fragmentation (as mandaory in IPv4) is not a good thing, and
we eliminated it for IPv6. Why do we hang on to fragmentation 
from the host when tranport layers would be better doing it than the IP
layer ?

Cheers
    Toerless

> > Aka: I would lvoe to see a new ICMPv4/ICMPv6 reply and/or PTB reply option
> > indicating "Fragmented Packets Not Permitted". Any network device which
> > for whatever reason does not like Fragemnts would simply drop
> > fragmented packets and send this as a reply. Allows then the
> > transport layer to automatically use packetization  (such as TCP MSS)
> > to get packets through.
> 
> I am not opposed to this option being created, but you still need PLPMTUD.
> This option might trigger faster PLPMTUD, but it doesn't make the problem go
> away. If the application still keeps sending packets that needs to be
> fragmented, what should the stack do, just send an error to the application?
> Yes, this will mean we will fail faster, but apart from that?
> 
> -- 
> Mikael Abrahamsson    email: swmike@swm.pp.se

-- 
---
tte@cs.fau.de