From owner-freebsd-net@FreeBSD.ORG Sun May 12 05:09:50 2013 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by hub.freebsd.org (Postfix) with ESMTP id 0C90AAAF for ; Sun, 12 May 2013 05:09:50 +0000 (UTC) (envelope-from kob6558@gmail.com) Received: from mail-ob0-x236.google.com (mail-ob0-x236.google.com [IPv6:2607:f8b0:4003:c01::236]) by mx1.freebsd.org (Postfix) with ESMTP id C8690AF0 for ; Sun, 12 May 2013 05:09:49 +0000 (UTC) Received: by mail-ob0-f182.google.com with SMTP id va2so101492obc.27 for ; Sat, 11 May 2013 22:09:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:x-received:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type; bh=6Ek0ADl8AlQY9NDZ/2dlTWYeMI31Ed/xBCjqd2VLcpA=; b=WCBNc8RcUnvzJF5JsiTvEPoY8AuMxTXpgaz14SvIUtOy9nL8mVEwbcsR2LLTGPlm9N zuop+NZ3NDwx3rjDUxAipkC2jS6XTMFPdEkSPMx+KqnkOhXsKUQqriXd51Bkiszkxvwu gG0M8nh2KRcj9DfVgVZPflNihdKeRRk8/bAzRoXD1uF0AlERD3xMMmwTQNn8E3v1wHCc AEWDk7GtDUzqgE9VDgwC+YDYf35gSmant47HvePDMXSnnE7adhDMiQ/ZCJNjcN++ncgb NIVLIdorsb8lzP/B0SArUH0Rpl4JkXozxHpNXz0DD8cGEbeeOmyUIzDaAUxza5wLHEdp 0MlQ== MIME-Version: 1.0 X-Received: by 10.182.165.131 with SMTP id yy3mr2115381obb.36.1368335389366; Sat, 11 May 2013 22:09:49 -0700 (PDT) Sender: kob6558@gmail.com Received: by 10.76.182.76 with HTTP; Sat, 11 May 2013 22:09:49 -0700 (PDT) In-Reply-To: <20130509.110631.74720486.sthaug@nethelp.no> References: <518B5F51.8020804@b0rken.org> <20130509.110631.74720486.sthaug@nethelp.no> Date: Sat, 11 May 2013 22:09:49 -0700 X-Google-Sender-Auth: vqcs4-ISk9k_3aIm3mRxhkFzcxU Message-ID: Subject: Re: IPv6 tunnel MTU of 1480 not effective From: Kevin Oberman To: sthaug@nethelp.no Content-Type: text/plain; charset=UTF-8 X-Content-Filtered-By: Mailman/MimeDel 2.1.14 Cc: jason@b0rken.org, freebsd-net@freebsd.org X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 12 May 2013 05:09:50 -0000 On Thu, May 9, 2013 at 2:06 AM, wrote: > > 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. > > > > This issue is evident when I try to send IPv6 pings larger than 1280 > > bytes to the remote tunnel peer. The outgoing echo request is chopped > > into two fragments, while the response comes back in one fragment, as > > follows: > > > > % ping6 -c 1 -s 1432 2001:470:1f08:84f::1 > > PING6(1480=40+8+1432 bytes) 2001:470:1f09:84f::2 --> 2001:470:1f08:84f::1 > > 1440 bytes from 2001:470:1f08:84f::1, icmp_seq=0 hlim=64 time=1.514 ms > > This is a "feature" (i.e. it's documented). See the ping6 -m option: > > -m By default, ping6 asks the kernel to fragment packets to fit into > the minimum IPv6 MTU. The -m option will suppress the behavior > in the following two levels: when the option is specified once, > the behavior will be disabled for unicast packets. When the > option is more than once, it will be disabled for both unicast > and multicast packets. > > In my opinion this behavior badly breaks POLA, and should be removed > (i.e. the current -m behavior should be the default). > > I have no great hope in getting this changed, though... > > Steinar Haug, Nethelp consulting, sthaug@nethelp.no > _ > Thanks, Steiner. 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. Please prove me wrong! -- R. Kevin Oberman, Network Engineer E-mail: rkoberman@gmail.com