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ipsec: Re: [IPsec] Fwd: Last Call: draft-ietf-ipsecme-ikev2-resu

Re: [IPsec] Fwd: Last Call: draft-ietf-ipsecme-ikev2-resumption (IKEv2 Session Resumption) to Proposed Standard

From: Yaron Sheffer <yaronf_at_nospam>
Date: Wed Sep 02 2009 - 21:15:40 GMT
To: Peny Yang <peng.yang.chn@gmail.com>, "ietf@ietf.org" <ietf@ietf.org>

Hi Peny,

Thank you for reviewing this draft. Please see my comments below.



> -----Original Message-----
> From: ipsec-bounces@ietf.org [mailto:ipsec-bounces@ietf.org] On Behalf Of
> Peny Yang
> Sent: Wednesday, September 02, 2009 17:18
> To: ietf@ietf.org
> Cc: IPsecme WG
> Subject: [IPsec] Fwd: Last Call: draft-ietf-ipsecme-ikev2-resumption
> (IKEv2 Session Resumption) to Proposed Standard
> Sorry, I should cc IPsec mail list. Comments are sent again.
> Hi, floks:
> I have two comments on the draft of IKEv2 Session Resumption:
> 1) Sorry, I have to talk about my concern on the new
> IKE_SESSION_RESUME. In WG last call, actually I made this comment.
> However, no feedback was given, maybe because my comment was a little
> late for WG last call. So, I just copy it here again as a comment for
> IESG last call.
> Well, we've discussed pros and cons of IKE_SA_INIT and
> IKE_SESSION_RESUME for quite a long time. However, IMHO, the consensus
> is still not fully achieved on this item. So far, I still prefer to
> choosing extended IKE_SA_INIT for ticket presenting. This solution is
> specified in http://tools.ietf.org/html/draft-xu-ike-sa-sync-01
> As a summary, the virtues are as follows:
> - RFC5077 (TLS session resumption) also uses the similar scheme, which
> extends the message of clienthello with session ticket extension. The
> extended IKE_SA_INIT solution has the similar way. It's easy to extend
> the base IKEv2 protocol stack to support session resumption.
> - Considering the case of failing session resumption, the extended
> IKE_SA_INIT solution can save one round trip.
> - As indicated in 4.3.3 IKE_AUTH exchange, IKE_AUTH must be initiated
> after IKE_SESSION_RESUME. In this sense, the extended IKE_SA_INIT way
> need less code to be supported compared with IKE_SESSION_RESUME.
> The down side:
> - some people thought the way of extended IKE_SA_INIT will make the
> base IKEv2 protocol stack more complex. IMHO, it's an issue of
> implementation.
> Again, I still support to use extended IKE_SA_INIT for ticket
> presenting instead of IKE_SESSION_RESUME.

[YS] I see the merits of extending IKE_SA_INIT to support resumption, and in fact an early version of our work did exactly that. But the working group gave us a clear direction to use a separate exchange, and this is where we disagree: I believe we did have a strong WG consensus that the implementation benefits of having a separate exchange (i.e. not overloading even more the non-trivial IKE_SA_INIT exchange) outweigh the benefits of the alternative.

> 2) Maybe I missed some discussions.
> There is the case: responder may receives a ticket for an IKE SA that
> is still active and if the responder accepts it. In one of previous
> versions of this draft, there once was some description on this case.

[YS] I believe you are referring to the text now in Sec. 4.3.4.

> I know that how a client detects the need for resumption is out of the
> scope of this draft. But, there is the possibility that IPsec client
> may be continuously deceived and believe the fail of IPsec gateway. It
> may continuously present the ticket and update the ticket. In this
> sense, IMHO, this draft should take care of this case.

[YS] If I understand the scenario correctly, it is similar to an attacker repeatedly sending notifications to an IKE client, making it believe that the IKE exchange has failed and needs to be reinitiated. This attack against plain-vanilla IKE would be much more CPU-intensive to the client and to the (real) gateway, compared to repeated session resumption. Even when you factor in the cost of generating a new ticket. Moreover, the regular IKEv2 anti-DOS cookie mechanism is supported by IKE_SESSION_RESUME as well.

> Peny
> On Mon, Aug 31, 2009 at 10:09 PM, The IESG<iesg-secretary@ietf.org> wrote:
> > The IESG has received a request from the IP Security Maintenance and
> > Extensions WG (ipsecme) to consider the following document:
> >
> > - 'IKEv2 Session Resumption '
> > <draft-ietf-ipsecme-ikev2-resumption-07.txt> as a Proposed Standard
> >
> > The IESG plans to make a decision in the next few weeks, and solicits
> > final comments on this action. Please send substantive comments to the
> > ietf@ietf.org mailing lists by 2009-09-14. Exceptionally,
> > comments may be sent to iesg@ietf.org instead. In either case, please
> > retain the beginning of the Subject line to allow automated sorting.
> >
> > The file can be obtained via
> > http://www.ietf.org/internet-drafts/draft-ietf-ipsecme-ikev2-resumption-
> 07.txt
> >
> >
> > IESG discussion can be tracked via
> >
> https://datatracker.ietf.org/public/pidtracker.cgi?command=view_id&dTag=17
> 990&rfc_flag=0
> >
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> >
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