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Re: [IPsec] I-D Action: draft-ietf-ipsecme-ikev2-fragmentation-03.txt

"Mike Sullenberger (mls)" <mls@cisco.com> Thu, 17 October 2013 18:34 UTC

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From: "Mike Sullenberger (mls)" <mls@cisco.com>
To: Valery Smyslov <svanru@gmail.com>
Thread-Topic: [IPsec] I-D Action: draft-ietf-ipsecme-ikev2-fragmentation-03.txt
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Date: Thu, 17 Oct 2013 18:34:02 +0000
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Cc: "ipsec@ietf.org" <ipsec@ietf.org>, Paul Wouters <paul@cypherpunks.ca>, "Mike Sullenberger (mls)" <mls@cisco.com>
Subject: Re: [IPsec] I-D Action: draft-ietf-ipsecme-ikev2-fragmentation-03.txt
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As I remember it IPv4 has a minimum packet size of 576 that won't (or at least shouldn't be) fragmented by IP.

Mike.


Mike Sullenberger, DSE
mls@cisco.com            .:|:.:|:.
Customer Advocacy          CISCO



> -----Original Message-----
> From: ipsec-bounces@ietf.org [mailto:ipsec-bounces@ietf.org] On Behalf
> Of Valery Smyslov
> Sent: Wednesday, October 09, 2013 10:34 PM
> To: Paul Wouters
> Cc: ipsec@ietf.org
> Subject: Re: [IPsec] I-D Action: draft-ietf-ipsecme-ikev2-fragmentation-
> 03.txt
> 
> >> I also think that PMTU discovery isn't very useful for IKE.
> >> That's why it is MAY.
> >
> > That does not help implementors who still have to implement the MAY's.
> > if even you as a document author does not think it is very useful,
> > then I think it should just not be in the document.
> 
> Sorry, I wasn't very clear. By "isn't very useful" I meant that it is not useful
> for the usual PMTU discovery goal in TCP - to find _maximum_ IP datagram
> size that is not fragmented by IP level. In IKE its the goal is different - to find
> _some_reasonable_ IP datagram size that is not fragmented by IP.
> 
> If we have the size that is guaranteed to not be fragmented, no PMTU
> discovery will be needed. As far as I understand, for IPv6 it is 1280 bytes. But
> as far as I know, there's no such value for IPv4.
> If we mandate (or recommend) using really small value e.g. 128 bytes, than
> the performance will suffer badly, so it is not a good option.
> I'm especially worrying about network I'm not familiar with - mobile
> networks or other constrained environments.
> It would be great if some experts in such networks could clarify this.
> 
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