Date: Sun, 12 May 2013 13:03:04 +0200 (CEST) From: sthaug@nethelp.no To: jinmei@isc.org Cc: rkoberman@gmail.com, freebsd-net@freebsd.org, jason@b0rken.org Subject: Re: IPv6 tunnel MTU of 1480 not effective Message-ID: <20130512.130304.74693108.sthaug@nethelp.no> In-Reply-To: <m2a9o063ds.wl%jinmei@isc.org> References: <20130509.110631.74720486.sthaug@nethelp.no> <CAN6yY1seGF8AP0%2BstgUaMUFBxvM9eAx5s1WgBLcpxE21pTFtTg@mail.gmail.com> <m2a9o063ds.wl%jinmei@isc.org>
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> > > > However I'm only able to send IPv6 packets from my host that fit an MTU > > > > of 1280 even though I've set the tunnel interface and per-route MTU to > > > > 1480, based on the "outer" ethernet connection having an MTU of 1500. > > > > Hurricane Electric supports this and I've set the MTU to 1480 on their > > > > side as well. > [...] > > I complained about this at least a couple of years ago and was told by the > > developer (I don't recall exactly who any more) that it was right and would > > not be changed. I really would love to see this reconsidered before IPv6 > > becomes much more popular as it will simply cause confusion, but I, too, > > fear that it is a lost cause. > > What's "this" (to reconsider)? That ping6 fragments outgoing packets > at 1280 octets (by default)? Or, more in general whether any outgoing > IPv6 packet can initially honor the interface MTU? What I want to happen is: When I use ping6 *and explicitly specify a packet size using the -s option*, I want the interface MTU to be honored. I don't want to have to specify -m as a sort of extra "yes, I really really mean it". This is, in my opinion, by far the least surprising behavior for the user - and would then work the same as the IPv4 ping command. It looks like an extremely simple change to make in the ping6.c file. (Long term, I would like ping and ping6 to become *one* program with default IPv4 or IPv6 based on the destination specified, and options -4 / -6 like telnet has. Same for traceroute / traceroute6. However, this is an aside.) Steinar Haug, Nethelp consulting, sthaug@nethelp.no
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