Date: Sat, 21 Jul 2007 12:02:56 -0500 From: Mike Karels <karels@karels.net> To: Artyom Viklenko <artem@aws-net.org.ua> Cc: freebsd-net@freebsd.org, Artem Belevich <fbsdlist@src.cx>, Julian Elischer <julian@elischer.org> Subject: Re: 6.2 mtu now limits size of incomming packet Message-ID: <200707211702.l6LH2ukt039317@redrock.karels.net> In-Reply-To: Your message of Sat, 21 Jul 2007 11:03:42 %2B0300. <46A1BDDE.5080403@aws-net.org.ua>
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> Any two hosts, connected to single Layer2 network MUST use > same MTU. Any other cases lead to hard-to-solve problems. I'd have to disagree. In fact, I'd say that any two hosts on the same L2 network must use the same MRU. In particular, if a host choses to use a lower MTU, if that also lowers the MRU, *that* is the cause of interoperability problems. David DeSimone <fox@verio.net> wrote: } You are correct about misconfigured networks. In my experience, } the only reason to ever reduce the MTU is to work around a problem } discovered in someone else's network (not my local segment). Fixing } the problem by getting someone else to fix their network is generally } too hard. If MTU == MRU was forced behavior, the viability of this } workaround would be removed, one less tool in the toolbag, so to speak. Exactly. In our local labs, we also reduce the MTU to test PMTU discovery. Requiring MRU == MTU makes this more difficult. True, it's a contrived situation, but as you say, one less tool in the toolbag. Mike
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