Re: Last Call: <draft-ietf-6man-rfc1981bis-04.txt> (Path MTU Discovery for IP version 6) to Internet Standard

Gorry Fairhurst <gorry@erg.abdn.ac.uk> Thu, 16 February 2017 14:08 UTC

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Subject: Re: Last Call: <draft-ietf-6man-rfc1981bis-04.txt> (Path MTU Discovery for IP version 6) to Internet Standard
References: <148599312602.18643.4886733052828400859.idtracker@ietfa.amsl.com> <1859B1D9-9E42-4D65-98A8-7A326EDDE560@netapp.com> <f8291774-409e-2948-3b29-83dbb09d39d9@si6networks.com> <63eaf82e-b6d5-bff5-4d48-479e80ed4698@gmail.com> <2d36e28c-ee7d-20fc-3fec-54561e520691@si6networks.com> <C0A114C1-5E4A-4B8E-A408-55AF1E30873F@netapp.com> <3A5429F6-0EA6-436A-AF30-E55C9026F456@employees.org> <8cf1fe7d-bdfd-5e81-e61f-55d9ecd5d28a@isi.edu> <7E9AB9E8-3FCB-4475-BEEB-F18CFC4BC752@employees.org> <8076a1ea-182d-9cbe-f954-3e50f0fc53d9@isi.edu> <E11F9A4D-DE9E-4BFD-8D0D-252842719FC5@employees.org> <619f0dc52a514f07a70b44126aeb66f3@XCH15-06-08.nw.nos.boeing.com> <da3de0a5-fe7f-c874-db1d-da2684619213@si6networks.com> <706163b815ef439bbd9e0a17eba83512@XCH15-06-08.nw.nos.boeing.com> <e201c72e-b7c1-5a5f-eacb-93896cd7a7bb@si6networks.com> <58A33D08.4090505@erg.abdn.ac.uk> <ed4e3ab5-e93e-d9ca-28c0-43f8bf22039a@isi.edu>
To: Joe Touch <touch@isi.edu>
From: Gorry Fairhurst <gorry@erg.abdn.ac.uk>
Organization: The University of Aberdeen is a charity registered in Scotland, No SC013683.
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Date: Thu, 16 Feb 2017 14:08:37 +0000
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The text below is not about tunnels - this is about  the operation of 
transport, and the quoted text is from the new UDP Guidelines ID.

On 15/02/2017 21:26, Joe Touch wrote:
> Hi, Gorry (et al.),
>
> Again, the following text should not drift into discussing how tunnels
> are handled IMO. That should be addressed in a different document (and I
> don't think it's troublesome at all if viewed correctly).
>
> Joe
>
>
> On 2/14/2017 9:23 AM, Gorry Fairhurst wrote:
>> - Introduces a significant vulnerability.  A rogue PTB message that
>> reduces the PMTU to a minimum, can result in a path too small to carry
>> an encapsulated packet. (Recently noted by Fernando Gont).
>>
>> Moreover, other layers view ICMP messages with suspicion and have long
>> noted the need to check ICMP payload and match only packets that
>> relate to actual 5-tuples in use (effectively reducing vulnerability
>> to off-path attacks). For example, the Guidelines for UDP, rfc5405bis,
>> state:
>>
>> " Applications SHOULD appropriately validate the payload of ICMP
>>    messages to ensure these are received in response to transmitted
>>    traffic (i.e., a reported error condition that corresponds to a UDP
>>    datagram actually sent by the application). …“

The comment below could easily be handled by something that clearly 
indicates the problem and points to the tunnel draft for guidance, I 
agree no need to go into algorithms/methods here.

>> - clearly handling this in IP-layer tunnels can be troublesome, but
>> that's a problem that should be described, not obscured.
>

Gorry