From owner-freebsd-net@FreeBSD.ORG Tue Jun 24 18:52:27 2014 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id B1D701C3 for ; Tue, 24 Jun 2014 18:52:27 +0000 (UTC) Received: from mail-qc0-x22f.google.com (mail-qc0-x22f.google.com [IPv6:2607:f8b0:400d:c01::22f]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 72FBA2C49 for ; Tue, 24 Jun 2014 18:52:27 +0000 (UTC) Received: by mail-qc0-f175.google.com with SMTP id i8so697976qcq.20 for ; Tue, 24 Jun 2014 11:52:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type; bh=joC0sVijymWPBhdukAfCfe/ODDFtqC+lx5JoCAifDqs=; b=HeO7xBmkSMYMAUJLM8K4EFQTnW8IfoNebltZQGPguN8FkfuaXplyvVm6M7Kf/Pr6bp 4UfkrvcH+Jwk76HZwYa8STl3H5TebyFZOYOGikMJBsQRt8Sl68izPCf5iufdruSlonjG eE5GmlDQFtePdffLvXZPzN8ZX2H4/FgEMe33uLM09BAfwjsGIcGcB4cyVJ5rdhwjZ75z +31Jp+iWKE+oD5W+p2MmfD52+Hd/6JChpKGr26bujq1dh9e78aXhtrbaCfDkJPCIIpLn j+eeSURoSD8PaCd18SWuneWa5qOcBi/A0JsHm29QREHwAZVg5CkokYu/KDcRxMxN//Mv i7Hg== X-Received: by 10.224.29.201 with SMTP id r9mr4683075qac.25.1403635946572; Tue, 24 Jun 2014 11:52:26 -0700 (PDT) MIME-Version: 1.0 Received: by 10.96.74.69 with HTTP; Tue, 24 Jun 2014 11:51:46 -0700 (PDT) In-Reply-To: <53A9C6D0.3090900@netfence.it> References: <53A9C6D0.3090900@netfence.it> From: Carlos Ferreira Date: Tue, 24 Jun 2014 19:51:46 +0100 Message-ID: Subject: Re: MTU not regrowing? To: Andrea Venturoli Content-Type: text/plain; charset=UTF-8 X-Content-Filtered-By: Mailman/MimeDel 2.1.18 Cc: "freebsd-net@freebsd.org" 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 18:52:27 -0000 don't forget the header of the ping. the -s flag specifies the amount of data that the ping carries. By specifying a size of 500, you are creating a ping packet larger than the MTU. On 24 June 2014 19:43, Andrea Venturoli wrote: > 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. > _______________________________________________ > freebsd-net@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org" > -- Carlos Miguel Ferreira Researcher at Telecommunications Institute Aveiro - Portugal Work E-mail - cmf@av.it.pt Skype & GTalk -> carlosmf.pt@gmail.com LinkedIn -> http://www.linkedin.com/in/carlosmferreira