Re: Last Call: <draft-ietf-6man-rfc1981bis-04.txt> (Path MTU Discovery for IP version 6) to Internet Standard Tue, 07 February 2017 21:32 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
Date: Tue, 07 Feb 2017 22:31:57 +0100
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To: Joe Touch <>
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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,