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RFC 8201 Packet Too Big Processing

Timothy Carlin <tjcarlin@iol.unh.edu> Fri, 10 April 2020 17:07 UTC

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From: Timothy Carlin <tjcarlin@iol.unh.edu>
Date: Fri, 10 Apr 2020 13:07:06 -0400
Message-ID: <CAB-aFv8wVjcXB73wLrBupbq3XLdmdMWE9i-8+TwHfYQE6V52_w@mail.gmail.com>
Subject: RFC 8201 Packet Too Big Processing
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Hello,

We've noticed during testing for RFC 8200 and 8201 that, for packets larger
than 1280, the Linux kernel is processing invalid Packet Too Big messages
that indicate an MTU less than 1280, and subsequently fragmenting packets
to a size of 1280. We've seen this with 4.15 and 4.18.

This is from Section 4 of RFC 8201:

>   If a node receives a Packet Too Big message reporting a next-hop MTU
>   that is less than the IPv6 minimum link MTU, it must discard it.

Have others noticed this issue with Linux or other OSes?  I'll also note
that it correctly does not generate an atomic fragment if the packet is
less than 1280 bytes.

Best Regards,
Tim Carlin
UNH-IOL

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