Re: [Plus] Supporting connection tracking and basic diagnostics: a minimal PLUS

"Christian Huitema" <huitema@huitema.net> Sun, 11 December 2016 16:47 UTC

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From: "Christian Huitema" <huitema@huitema.net>
To: "'Ian Swett'" <ianswett@google.com>
References: <83EEC537-3486-4864-ACA2-911F570D0C57@trammell.ch> <15261501-1F9C-41CA-87D0-4E8FCD862044@trammell.ch> <CAKcm_gMzw9Z=XnFy9vYfxOOG+eO6XJ2bSNeboQYjxW+MOUwa9g@mail.gmail.com> <E4BB21D8-9747-409C-BCF7-E62029897282@apple.com> <02ec01d25378$83799550$8a6cbff0$@huitema.net> <CAKcm_gPHUQ-EYrC1SHEXj6vpSMdEqmqZufdWLpxJxnVLZ0ZwYg@mail.gmail.com>
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Date: Sun, 11 Dec 2016 08:47:05 -0800
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Cc: 'Brian Trammell' <ietf@trammell.ch>, 'Tommy Pauly' <tpauly@apple.com>, plus@ietf.org
Subject: Re: [Plus] Supporting connection tracking and basic diagnostics: a minimal PLUS
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On Sunday, December 11, 2016 6:51 AM, Ian Swett wrote:
> On Sun, Dec 11, 2016 at 1:33 AM, Christian Huitema <mailto:huitema@huitema.net> wrote:
>> ...OTOH, there is going to be a "feature interaction" between this sequence+echo scheme and 
>> the senders' strategy of skipping some sequence numbers in order to verify that the recipients
>> are not making up ACKS. The intermediate boxes will have no way to distinguish between a 
>> packet number voluntarily skipped by the sender, and a packet loss between the sender and
>> the middlebox. I hope this won't affect the "wireshark diagnostics" too much.
>
> We could specify that if a peer wants to skip packet numbers, it should be by more than 256,
> assuming 256 packet gaps are rare(which they are, though they do happen).    Or some other 
> known approach that is relatively simple to identify.

If you make it easier to identify, then you defeat the purpose of the packet skipping. Suppose a bad receiver, intent on setting a DOS attack. Its strategy is to ACK as quickly as possible, regardless of losses. The sender detects ACK of packets that were not sent, and aborts the connection. But if the skipping is easy to detect by middleboxes, it is also easy to detect by the bad receiver, which will suspend its ACK everything strategy if it detects a test...

-- Christian Huitema