From owner-freebsd-net@FreeBSD.ORG Tue Apr 1 14:48:07 2014 Return-Path: Delivered-To: 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 79CB0B59 for ; Tue, 1 Apr 2014 14:48:07 +0000 (UTC) Received: from os-mail-3.tamu.edu (os-mail-3.tamu.edu [165.91.23.217]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "mail.tamu.edu", Issuer "InCommon Server CA" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 18EDBC92 for ; Tue, 1 Apr 2014 14:48:06 +0000 (UTC) X-TAMU-Auth-ID: daved X-TAMU-SenderIP: 128.194.60.151 X-HAT: SG None, P $RELAY, L incoming_auth X-SRBS: None X-EXTLoop1: 128.194.60.151 X-IronPort-AV: E=Sophos;i="4.97,773,1389765600"; d="scan'208";a="437556213" Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 6.6 \(1510\)) Subject: Re: questions about (system) dhclient From: Dave Duchscher In-Reply-To: Date: Tue, 1 Apr 2014 09:46:58 -0500 Content-Transfer-Encoding: 7bit Message-Id: <628086E4-3832-4221-B33E-9AC9234F3076@tamu.edu> References: <5339D0A0.1030903@rcn.com> To: Rick Miller X-Mailer: Apple Mail (2.1510) Cc: Robert Huff , net@freebsd.org X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.17 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, 01 Apr 2014 14:48:07 -0000 On Apr 1, 2014, at 7:48 AM, Rick Miller wrote: > On Mon, Mar 31, 2014 at 4:31 PM, Robert Huff wrote: > >> [Please keep me CC'd as I am not subscribed. Thanks.] >> >> I have a system, running r263263, where dhclient is misbehaving. >> (Yes - this is CURRENT, but I have no reason to believe this inherently a >> version-specific issue. I am also on current@, and nothing like this has >> been reported.) >> The system has an Intel Pro/1000 ethernet card, "em0", connected >> to a Arris CM820 cable modem. >> This is the relevant portion of dhclient.conf: >> >> http://users.rcn.com/dhclient.conf >> >> Upon execution, I get this: >> >> http://users.rcn.com/roberthuff/dhcp_offer > > > The conversation between a DHCP server and client consists of the initial > DHCP DISCOVER request from the client broadcasted to the network to which a > DHCP ACK is expected in reply from an available DHCP server. Upon receipt > of DHCP ACK, the client sends another DHCP DISCOVER to the server asking > for configuration information necessary to initialize networking. The > server's response is a DHCP OFFER containing all the information requested > by the client. > > I illustrate this in a sequence diagram describing a PXE workflow for > FreeBSD installation at > http://hostileadmin.com/images/FreeBSD_PXE_Install_Workflow.gif. The first > four steps in the sequence is the workflow's first DHCP conversation. The description of the DHCP packet flow is incorrect. DHCP packet flow is the following for clients requesting a new lease. Diagram below copied from RFC 2131. For clients renewing a lease, only the REQUEST and ACK steps are done. Server Client Server (not selected) (selected) v v v | | | | Begins initialization | | | | | _____________/|\____________ | |/DHCPDISCOVER | DHCPDISCOVER \| | | | Determines | Determines configuration | configuration | | | |\ | ____________/ | | \________ | /DHCPOFFER | | DHCPOFFER\ |/ | | \ | | | Collects replies | | \| | | Selects configuration | | | | | _____________/|\____________ | |/ DHCPREQUEST | DHCPREQUEST\ | | | | | | Commits configuration | | | | | _____________/| | |/ DHCPACK | | | | | Initialization complete | | | | . . . . . . | | | | Graceful shutdown | | | | | |\ ____________ | | | DHCPRELEASE \| | | | | | Discards lease | | | v v v Figure 3: Timeline diagram of messages exchanged between DHCP client and servers when allocating a new network address -- DaveD