Date: Sat, 21 Jul 2007 11:05:47 +0300 From: Artyom Viklenko <artem@aws-net.org.ua> To: Eli Dart <dart@es.net> Cc: freebsd-net@freebsd.org, Julian Elischer <julian@elischer.org> Subject: Re: 6.2 mtu now limits size of incomming packet Message-ID: <46A1BE5B.60509@aws-net.org.ua> In-Reply-To: <46A10860.50804@es.net> References: <200707150237.l6F2bAgZ011098@redrock.karels.net> <469E0FFF.8070802@seclark.us> <20070720172021.8EA3D13C4B3@mx1.freebsd.org> <46A10063.9010902@elischer.org> <46A10860.50804@es.net>
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Eli Dart wrote:
>
> The networks that are apparently working fine are most likely
> misconfigured, IMHO.
>
> Others have made a case for permitting an interface to accept as large a
> packet as it can, regardless of configured MTU. That's fine for theory.
>
> My operational experience leads me to a different place. If an
> interface receives a packet that is larger than its configured MTU, I
> would prefer that the packet be dropped as a giant and a giants counter
> incremented, regardless of whether the hardware can theoretically
> receive the packet. In modern networks, an MTU mismatch within a
> broadcast domain indicates a broken network, IMHO. If the devices in
> the network are configured to enforce MTU for both tx and rx, more
> problems get spotted during turnup, rather than surfacing later on as
> difficult-to-diagnose problems that users only call about after they are
> truly frustrated. And, if you have a giants counter (or input error
> counter) you can look at, it makes it straightforward to spot the problem.
>
> (one could also stretch a bit and say that enforcing MTU on rx might
> provide less surprise to code that consumes packets and has knowledge of
> the MTU setting of an interface.....unfortunately I don't know enough
> about the details of the network stack to know if this is a real concern)
100% agree! :)
--
Sincerely yours,
Artyom Viklenko.
-------------------------------------------------------
artem@aws-net.org.ua | http://www.aws-net.org.ua/~artem
FreeBSD: The Power to Serve - http://www.freebsd.org
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