RE: [EXT] Re: Last Call: <draft-ietf-6man-rfc2460bis-08.txt> (Internet Protocol, Version 6 (IPv6) Specification) to Internet Standard

Tal Mizrahi <talmi@marvell.com> Tue, 14 February 2017 13:37 UTC

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From: Tal Mizrahi <talmi@marvell.com>
To: Mark Smith <markzzzsmith@gmail.com>
Subject: RE: [EXT] Re: Last Call: <draft-ietf-6man-rfc2460bis-08.txt> (Internet Protocol, Version 6 (IPv6) Specification) to Internet Standard
Thread-Topic: [EXT] Re: Last Call: <draft-ietf-6man-rfc2460bis-08.txt> (Internet Protocol, Version 6 (IPv6) Specification) to Internet Standard
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Date: Tue, 14 Feb 2017 13:37:10 +0000
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Hi Mark,

I certainly agree that hop-by-hop insertion/modification introduces potential security vulnerabilities.
Therefore, as I pointed out below, I would recommend to tackle this by defining something along the lines of “Hop-by-hop extensions can be inserted/removed/modified/processed by intermediate nodes *if* [……..] and the possible consequences are [……..]”

For example, hop-by-hop handling can be restricted only to a single administrative domain, or only to tunnels (as in the zero checksum case). 

Regards,
Tal.

>-----Original Message-----
>From: Mark Smith [mailto:markzzzsmith@gmail.com]
>Sent: Monday, February 13, 2017 6:07 PM
>To: Tal Mizrahi
>Cc: 6man@ietf.org; IETF Discussion list; draft-ietf-6man-
>rfc2460bis@tools.ietf.orgorg; 6man-chairs@ietf.org
>Subject: [EXT] Re: Last Call: <draft-ietf-6man-rfc2460bis-08.txt> (Internet
>Protocol, Version 6 (IPv6) Specification) to Internet Standard
>
>External Email
>
>----------------------------------------------------------------------
>Hi,
>
>
>
>On 14 February 2017 at 00:43, Tal Mizrahi <talmi@marvell.com> wrote:
>> Hi,
>>
>>
>>
>> Good discussion regarding the text about the hop-by-hop extension.
>>
>>
>>
>> In my opinion there is a valid use case for intermediate nodes that
>> insert/remove/modify/process hop-by-hop extensions. Examples: IOAM, INT.
>>
>> Since there is a use case, I believe we need explicit text about
>> intermediate handling of hop-by-hop extensions.
>>
>
>
>Imagine you sent a letter through the postal system, and the postal system
>wanted to add information to that letter, that is then to be removed before the
>letter arrives at its final destination.
>
>The postal system have at least two choices as to how to add that information.
>They could:
>
>(a) unstick your envelope's seal, insert the information, reseal the envelope so
>well you can't tell and send it on its way, some how flagging to a destination
>device within the postal system that this specific envelop needs to be openned, a
>specific page removed, and then resealed.
>
>(b) take a new envelope with new internal postal system source and destination
>address information, insert your letter without touching it in addition to the new
>information, and then sending it on its way.
>
>Imagine that the information to be added by the postal system is printed on the
>same type of paper and is written in the same font as you've chosen to use to
>write your letter.
>
>Have a think about these two methods, what could fail with each of them, and
>what the consequences may be if any of those failures occur.
>Have a think of the benefits of each method, and whether they're worth it
>compared to the failure mode costs and consequences for the method.
>
>>
>>
>> This [somewhat] reminds me of the discussion a few years ago about the
>> IPv6/UDP zero checksum. The WG ended up defining that “Zero checksum
>> is permitted in IPv6/UDP *if* [……..] and the possible consequences are [……..]”.
>>
>>
>
>That is a far more trivial change to the packet - it is allowing a value in an existing
>field that was formerly prohibited, and nodes that did not understand that value
>would drop the packet because that is what they had been specified to do if they
>received this prohibited value. In other words, existing implementations '
>behaviour when this formerly unexpected value was encountered had already
>been specified and deployed.
>
>
>>
>> I would argue that regarding hop-by-hop extension handling we also
>> need to define that “Hop-by-hop extensions can be
>> inserted/removed/modified/processed by intermediate nodes *if* [……..]
>> and the possible consequences are [……..]”.
>>
>
>Some things that are possible to do in theory shouldn't be done in practice,
>because the consequences when their implementations fail can be severe and
>outweigh the benefits.
>
>In theory, inserted EHs will be removed 100% of the time. In practice they won't
>be, because implementations can have bugs and they can also fail in unexpected
>ways e.g., hardware faults.
>
>Regards,
>Mark.