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

Joe Touch <touch@isi.edu> Tue, 07 February 2017 21:36 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
To: otroan@employees.org
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From: Joe Touch <touch@isi.edu>
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Date: Tue, 7 Feb 2017 13:35:50 -0800
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IMO it's worth including a sentence that highlights these things
elsewhere in the doc.

But if others disagree, the existing text is sufficient.

Joe


On 2/7/2017 1:31 PM, otroan@employees.org wrote:
> Thanks Joe.
>
>> I'd add one sentence about Fred's observation too:
>>
>> In addition, spoofed ICMP messages can also affect the correct operation
>> of PMTUD.
> You don't think that's covered by the existing security considerations:
>
>    This Path MTU Discovery mechanism makes possible two denial-of-
>    service attacks, both based on a malicious party sending false Packet
>    Too Big messages to a node.
>
>    In the first attack, the false message indicates a PMTU much smaller
>    than reality.  This should not entirely stop data flow, since the
>    victim node should never set its PMTU estimate below the IPv6 minimum
>    link MTU.  It will, however, result in suboptimal performance.
>
>    In the second attack, the false message indicates a PMTU larger than
>    reality.  If believed, this could cause temporary blockage as the
>    victim sends packets that will be dropped by some router.  Within one
>    round-trip time, the node would discover its mistake (receiving
>    Packet Too Big messages from that router), but frequent repetition of
>    this attack could cause lots of packets to be dropped.  A node,
>    however, should never raise its estimate of the PMTU based on a
>    Packet Too Big message, so should not be vulnerable to this attack.
>
> Best regards,
> Ole
>