Date: Tue, 1 Apr 2014 09:46:58 -0500 From: Dave Duchscher <daved@tamu.edu> To: Rick Miller <vmiller@hostileadmin.com> Cc: Robert Huff <roberthuff@rcn.com>, net@freebsd.org Subject: Re: questions about (system) dhclient Message-ID: <628086E4-3832-4221-B33E-9AC9234F3076@tamu.edu> In-Reply-To: <CAHzLAVGGR--GzG%2BzO80HLwPh-88e-2LswP5kaLHya1UqV1Kp6g@mail.gmail.com> References: <5339D0A0.1030903@rcn.com> <CAHzLAVGGR--GzG%2BzO80HLwPh-88e-2LswP5kaLHya1UqV1Kp6g@mail.gmail.com>
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On Apr 1, 2014, at 7:48 AM, Rick Miller <vmiller@hostileadmin.com> wrote: > On Mon, Mar 31, 2014 at 4:31 PM, Robert Huff <roberthuff@rcn.com> 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
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