Re: [IPsec] Comments on draft-ietf-ipsecme-tcp-encaps

[Eric Rescorla <[e-mail]>]

Thanks for the explanation...

-Ekr


On Sun, Mar 19, 2017 at 11:45 AM, Tommy Pauly <[e-mail]> wrote:

> Some servers may support that, but some may not. These sessions are often
> used for VPN access, and we've seen cases in which a particular
> user/certificate combination is only allowed to be connected
> once-at-a-time. That makes switching more complicated. Also, since the
> recommendation is to try sending the UDP first packet at least twice, the
> amount of time required for the user to wait before the fallback would kick
> in is only on the order of a few RTT.
>
> I think if these session were more likely to be used for user-interactive,
> short-lived connections, I'd see more value in a nuanced racing algorithm.
> However, we often see IKE brought up in the background and stay associated
> for a very long time, making the protocol that wins the race more
> important, and the time to wait to establish slightly less important.
>
> Thanks,
> Tommy
>
> > On Mar 19, 2017, at 11:40 AM, Eric Rescorla <[e-mail]> wrote:
> >
> > I haven't fully thought this through, but if yu can switch-hit between
> TCP
> > and UDP,
> > why can't you just race the setup between TCP and UDP and then if you
> start
> > getting packets on UDP, cut over to that.
> >
> > Maybe I'm just too influenced by ICE :)
> >
> > -Ekr
> >
> >
> > On Sun, Mar 19, 2017 at 11:25 AM, Tommy Pauly <[e-mail]> wrote:
> >
> >>
> >> On Mar 19, 2017, at 6:47 AM, Eric Rescorla <[e-mail]> wrote:
> >>
> >>
> >>
> >> On Sat, Mar 18, 2017 at 11:29 PM, Yoav Nir <[e-mail]> wrote:
> >>
> >>> Hi, Eric.
> >>>
> >>> On 19 Mar 2017, at 4:04, Eric Rescorla <[e-mail]> wrote:
> >>>
> >>> [Now with the right address]
> >>>
> >>> I just finished reading this document. Some comments below.
> >>>
> >>>
> >>> - You have a uniform 16 bit length field followed by a 4 byte all-zeros
> >>>   sentinel value to indicate that a packet is IKE rather than ESP.
> >>>   Given that in S 3 graf 2 you have a SHOULD-level requirement
> >>>   to use typical UDP payload lengths, why not instead explicitly
> >>>   limit lengths to 15 bits and use the top bit to indicate IKE versus
> >>>   ESP. This would be slightly more efficient and seems simpler.
> >>>   I suppose that the counterargument is that IKE over UDP behaves
> >>>   differently, but in terms of implementation, that doesn't seem like
> >>>  much of an argument.
> >>>
> >>>
> >>> Another counter-argument is that we sometimes need the entire
> theoretical
> >>> length of a UDP packet. The IKE_AUTH messages typically carry a
> certificate
> >>> chain and sometimes even a CRL. And there is no way to split a
> certificate
> >>> chain over several messages. With remote access VPN you also get a CFG
> >>> payload with configuration information that can also encode an
> unbounded
> >>> amount of data. So I would not want to constrain the certificate chains
> >>> that we are able to send any more than the IP packet length already
> does
>
>