Re: npf: nbuf_ensure_contig and large options

[mlelstv%serpens.de@localhost (Michael van Elst)]

rmind%netbsd.org@localhost (Mindaugas Rasiukevicius) writes:

>Maxime Villard <max%m00nbsd.net@localhost> wrote:
>> There probably aren't many reasons for an IPv6 packet to have an option
>> located this far, but that's theoretically possible, and more importantly,
>> correct specwise.


>I do not see that as an NPF problem.  It expects the network stack to
>support certain operations and, in this case, it is a limitation of the
>mbuf interface and m_ensure_contig().

Please also see RFC 7112.

"As a result of the above-mentioned requirement, a packet's header
 chain length cannot exceed the Path MTU associated with its
 destination.  Hosts discover the Path MTU using procedures such as
 those defined in [RFC1981] and [RFC4821].  Hosts that do not discover
 the Path MTU MUST limit the IPv6 Header Chain length to 1280 bytes.
 Limiting the IPv6 Header Chain length to 1280 bytes ensures that the
 header chain length does not exceed the IPv6 minimum MTU [RFC2460]."

While that's not directly related to mbufs, I would guess that general
support for jumbo packets in the stack would require us to provide
larger mbufs that would again ensure that one mbuf can carry one
packet and thus one complete header chain. Current ethernet and
internet MTUs are not a real problem.

-- 
-- 
                                Michael van Elst
Internet: mlelstv%serpens.de@localhost
                                "A potential Snark may lurk in every tree."