From owner-freebsd-net@FreeBSD.ORG Sun Oct 26 15:25:27 2008 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 6A82A106566B for ; Sun, 26 Oct 2008 15:25:27 +0000 (UTC) (envelope-from eitans@mellanox.co.il) Received: from mellanox.co.il (mail.mellanox.co.il [194.90.237.43]) by mx1.freebsd.org (Postfix) with ESMTP id 63F1F8FC1D for ; Sun, 26 Oct 2008 15:25:25 +0000 (UTC) (envelope-from eitans@mellanox.co.il) Received: from Internal Mail-Server by MTLPINE1 (envelope-from eitans@mellanox.co.il) with SMTP; 26 Oct 2008 16:58:42 +0200 X-MimeOLE: Produced By Microsoft Exchange V6.5 Content-class: urn:content-classes:message MIME-Version: 1.0 Date: Sun, 26 Oct 2008 16:58:33 +0200 Message-ID: <5D49E7A8952DC44FB38C38FA0D758EADC72E72@mtlexch01.mtl.com> X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: I seems that the OS does use the available MTU Thread-Index: Ack3e1EQIZy6XDDeS5yFRz46zToseg== From: "Eitan Shefi" To: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Cc: Eitan Shefi Subject: I seems that the OS does use the available MTU X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 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, 26 Oct 2008 15:25:27 -0000 Hi, =20 I am using 2 hosts with FreeBSD-7.0 connected directly. When I change the MTU to a value greater then 1500, for example 3000, and then send "ping" with message size 2500, from one host to the other, the other host gets more then one ICMP packet, even thaw the message that was send is match smaller then the MTU. =20 I tried to run this test using a different NIC, but I got the same behavior. =20 I run: 1. On both hosts: ifconfig mtnic0 mtu 3000 2. Than on one host I run: tcpdump -i mtnic0 icmp 3. And on the other host I run: ping -s 2500 -c 1 OTHER_HOST_IP (ping to "mtnic0" on the other host) =20 On the receiving side I get the output: =20 [root@sw260 ~]# tcpdump -i mtnic0 icmp tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on mtnic0, link-type EN10MB (Ethernet), capture size 96 bytes 13:12:45.904454 IP 11.4.12.5 > 11.4.12.6: ICMP echo request, id 22550, seq 0, length 1480 13:12:45.904463 IP 11.4.12.5 > 11.4.12.6: icmp 13:12:45.904477 IP 11.4.12.6 > 11.4.12.5: ICMP echo reply, id 22550, seq 0, length 1480 13:12:45.904480 IP 11.4.12.6 > 11.4.12.5: icmp =20 Please help resolving this issue. =20 =20 Thanks, =20 Eitan Shefi