From owner-freebsd-net Thu Feb 10 20: 6:54 2000 Delivered-To: freebsd-net@freebsd.org Received: from ind.alcatel.com (postal.xylan.com [208.8.0.248]) by builder.freebsd.org (Postfix) with ESMTP id 538E74639 for ; Thu, 10 Feb 2000 20:06:46 -0800 (PST) Received: from mailhub.xylan.com (mailhub [198.206.181.70]) by ind.alcatel.com (8.9.3+Sun/8.9.1 (ind.alcatel.com 3.0 [OUT])) with SMTP id UAA09909; Thu, 10 Feb 2000 20:05:16 -0800 (PST) X-Origination-Site: Received: from omni.xylan.com by mailhub.xylan.com (SMI-8.6/SMI-SVR4 (mailhub 2.1 [HUB])) id UAA20113; Thu, 10 Feb 2000 20:05:16 -0800 Received: from softweyr.com (dyn5.utah.xylan.com [198.206.184.241]) by omni.xylan.com (8.9.3+Sun/8.9.1 (Xylan engr [SPOOL])) with ESMTP id UAA09269; Thu, 10 Feb 2000 20:05:14 -0800 (PST) Message-ID: <38A38BEA.146E6526@softweyr.com> Date: Thu, 10 Feb 2000 21:11:22 -0700 From: Wes Peters Organization: Softweyr LLC X-Mailer: Mozilla 4.7 [en] (X11; U; FreeBSD 3.3-RELEASE i386) X-Accept-Language: en MIME-Version: 1.0 To: Garrett Wollman Cc: Stephen Macmanus , freebsd-net@freebsd.org Subject: Re: Path MTU discovery cutoff References: <200002102308.PAA18465@brisbane.wrs.com> <200002110146.UAA44355@khavrinen.lcs.mit.edu> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-freebsd-net@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org Garrett Wollman wrote: > > < said: > > > RFC 1191 specifies a minimum path MTU estimate of 68 bytes for a > > participating host. The FreeBSD 3.4 implementation uses a cutoff > > of 296 bytes. Why does it have a larger minimum? > > Because when I felt that the RFC-specified minimum was unreasonably > small, and if people want to have links with tiny MTUs then they > should bear the costs themselves. It's also protection against a > PMTU-DoS attack. Is this a candidate for a sysctl knob? sys.net.inet.ip.minmtu, with a default value of 296, so we can be fully RFC compliant and yet sensible? -- "Where am I, and what am I doing in this handbasket?" Wes Peters Softweyr LLC wes@softweyr.com http://softweyr.com/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message