From owner-freebsd-net@FreeBSD.ORG Tue Jun 24 18:43:50 2014 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id A5D72FA2 for ; Tue, 24 Jun 2014 18:43:50 +0000 (UTC) Received: from mp1-smtp-5.eutelia.it (mp1-smtp-5.eutelia.it [62.94.10.165]) by mx1.freebsd.org (Postfix) with ESMTP id 5AA9F2B6B for ; Tue, 24 Jun 2014 18:43:50 +0000 (UTC) Received: from ns2.biolchim.it (ip-188-188.sn2.eutelia.it [83.211.188.188]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mp1-smtp-5.eutelia.it (Eutelia) with ESMTP id 437CC1747C7 for ; Tue, 24 Jun 2014 20:43:42 +0200 (CEST) Received: from soth.ventu (adsl-ull-205-226.41-151.net24.it [151.41.226.205]) (authenticated bits=0) by ns2.biolchim.it (8.14.9/8.14.8) with ESMTP id s5OIhblp043607 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=FAIL) for ; Tue, 24 Jun 2014 20:43:38 +0200 (CEST) (envelope-from ml@netfence.it) X-Authentication-Warning: ns2.biolchim.it: Host adsl-ull-205-226.41-151.net24.it [151.41.226.205] claimed to be soth.ventu Received: from alamar.ventu (alamar.ventu [10.1.2.18]) by soth.ventu (8.14.9/8.14.7) with ESMTP id s5OIhSgF051149 for ; Tue, 24 Jun 2014 20:43:28 +0200 (CEST) (envelope-from ml@netfence.it) Message-ID: <53A9C6D0.3090900@netfence.it> Date: Tue, 24 Jun 2014 20:43:28 +0200 From: Andrea Venturoli User-Agent: Mozilla/5.0 (X11; FreeBSD i386; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: freebsd-net@freebsd.org Subject: MTU not regrowing? Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.4.3 (ns2.biolchim.it [192.168.2.203]); Tue, 24 Jun 2014 20:43:38 +0200 (CEST) X-Scanned-By: MIMEDefang 2.74 X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 24 Jun 2014 18:43:50 -0000 Hello. Today I experienced something weird (at least for me) on a 8.4 system: _ the system had vlan3 interface, with default MTU (1500 bytes); _ "ping -D -s 1400 somehost" would work, but "ping -D -s 1500 somehost" would yield "frag needed and DF set" (forgive me if the message is not exact, I don't have it anymore); _ to make some tests I reduced MTU size with "ifconfig vlan3 mtu 500"; _ now, of course, "ping -D -s 400 somehost" would work, but "ping -D -s 500 somehost" would yield "frag needed and DF set"; _ then I raised MTU again with "ifconfig vlan3 mtu 1500" (notice ifconfig would actually report this as "mtu 1500" was shown); _ however the results were as before, i.e. "ping -D -s 400 somehost" would work, but "ping -D -s 500 somehost" would yield "frag needed and DF set"; _ no way I could ping with a packet bigger than 500 bytes until I rebooted. Is this expected behaviour? Any way to get around this? bye & Thanks av.