[tcpm] draft-ietf-tcpm-tcp-uto-02
Gorry Fairhurst <gorry@erg.abdn.ac.uk> Tue, 15 November 2005 09:43 UTC
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Date: Sat, 12 Nov 2005 17:30:28 +0000
From: Gorry Fairhurst <gorry@erg.abdn.ac.uk>
To: tcpm@ietf.org, Lars Eggert <lars.eggert@netlab.nec.de>, fernando@gont.com.ar
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Cc: gorry@erg.abdn.ac.uk, Ted Faber <faber@isi.edu>, "mallman@icir.org" <mallman@icir.org>
Subject: [tcpm] draft-ietf-tcpm-tcp-uto-02
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The authors requested a review of the UTO mechanism. First my comments on the case for the method: 1) One major problem with this document is that it is hard to see what it is about, until you are well into the document. If I understand correctly, it is about a TCP Option for a receiver to request a sender to alter the time interval it will wait for a data segment to be acknowledged. 2) I don't yet see a compelling reason why this has to be negotiated at the TCP-layer. This needs to be made clear. The new method does not completely relieve the need for new code - Applications still need to add (some) code to use the new socket option. 3) If I understand, the mechanism is also per-direction of data transfer - that is there is no *necessity* for both end hosts to agree on the same values - although there are cases where they may both wish to (e.g.) increase the default. 4) My biggest worry that the current mechanism allows a remote party to alter the behaviour of a sender, without the prior consent of the host application. This seems wrong. I suggest it is important to consider whether this is "sane" - it needs thought. On the other hand, if the application calls-down the socket API saying this is allowed, then this is fine, and I would have no problems on this point. -------- Now comments on the protocol: 1) The wording describes sending the option in either/both the SYN v. established states. The protocol should be made clearer about this. If an end-host SENDS the option in a SYN packet, is it expected in the SYN-ACK? - One thing that I think needs thought is that in the currently defined method the Option in a SYN indicates "I may tell you that I wish to use a different UTO" - In fact the exact opposite is much more useful tgo the remote party: A SYN packet that carries an option saying "MY UTO is XXXX, you may change it". 2) A separate point, relating to options is that normal TCP behaviour REQUIRES an option to be present in the SYN to use it later. Is it REQUIRED to send this option in the SYN packet to be allowed to later use this once the session is established? 3) [anchor3]. This (the case for other timer changes) needs explained, if the WG does need to define more than a UTO and this is also needed let's do it in a consistent way (in this document, or decide not to). - I believe the decision needs to be made! 4) Too low a UTO can be VERY harmful to the network service. I believe it is very important to establish and define a sensible minimal value. All to many times applications developers write and test code in a LAN environment and only later deploy in the general Internet. We should not provide another opportunity for people to use TCP in cute ways that will break on arbitrary Internet paths! I think the minimum UTO must be REQUIRED. 5) I really feel uneasy about the idea of responding to a UTO option with another UTO option. This seems bad protocol design, and should at least be damped by imposing a minimum time before the response can be sent. Why do this? - I change my end, I request you to change yours. Is that not it done? I think that we can not afford for an incompatibility throwing packets backwards and forwards for ever, if that means defining another TCP Option, to inform of the change, then that needs to be thought about. 6) Are there situations in which you wish to allow the UTO to be reduced once the session has started. Allowing reduction of the UTO below the actual PRTT (whatever that means in practice) provides a DOS vulnerability. Another thing to note here, if I understand, is that reducing the UTO may immediately cause the session to close (if data was unacknowledged). 7) Are there any interoperability issues with NATs/Middleboxes when this is included on a SYN packet? Best wishes, Gorry Fairhurst P.S. One way to fix the Min UTO problem would be to set the units of measure as minutes .... ;-) ---- Some NiTs, /on a satellite/on a non-geostationary satellite/ - All satellites orbit, but the vast majority used for telecoms take an orbit that is goeostationary. /This document specifies.../ IMHO, this should come at the start, and would help clarify what the I-D is about. I do not see the necessity of the following refs: [SCHUETZ-THESIS] [SCHUETZ-CCR] [DRIVE-THRU]. There check the use of SHOULD and MUST in capitals [RFC2119]. _______________________________________________ tcpm mailing list tcpm@ietf.org https://www1.ietf.org/mailman/listinfo/tcpm
- [tcpm] draft-ietf-tcpm-tcp-uto-02 Gorry Fairhurst
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Fernando Gont
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Gorry Fairhurst
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Fernando Gont
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Wesley Eddy
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Gorry Fairhurst
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Ted Faber
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Fernando Gont
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Ted Faber
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Gorry Fairhurst
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Ted Faber
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Fernando Gont
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Fernando Gont
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Fernando Gont
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Gorry Fairhurst
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Ted Faber
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Ted Faber
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Lars Eggert
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Fernando Gont
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Ted Faber
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Gorry Fairhurst
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Fernando Gont
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Joe Touch
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Fernando Gont
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Gorry Fairhurst
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Fernando Gont
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Gorry Fairhurst
- Re: [tcpm] draft-ietf-tcpm-tcp-uto-02 Fernando Gont