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Date:      Sun, 14 Aug 2011 15:35:21 +0800
From:      dave jones <s.dave.jones@gmail.com>
To:        "Christopher J. Ruwe" <cjr@cruwe.de>
Cc:        "freebsd-questions@freebsd.org" <freebsd-questions@freebsd.org>
Subject:   Re: How to get ip address automatically from different dhcp server
Message-ID:  <CANf5e8atq2-L578vo8uu_n=S0b_9+aaeCa3bafze-bQv50NJ+Q@mail.gmail.com>
In-Reply-To: <20110812203204.931270c4.cjr@cruwe.de>
References:  <CANf5e8ZtkdWZhM6f=MeWv6+mNJOZ75jjox28Ss7L9RWpGNG3=g@mail.gmail.com> <20110727223034.0c0f0c8d@dijkstra> <CANf5e8bHvznRJmZ=j0T3gJ3jdf3=piUdCNSOvQx4DgQ-ukYJTA@mail.gmail.com> <20110812203204.931270c4.cjr@cruwe.de>

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On Sat, Aug 13, 2011 at 2:32 AM, Christopher J. Ruwe  wrote:
> On Fri, 12 Aug 2011 11:46:34 +0800
> dave jones <s.dave.jones@gmail.com> wrote:
>
> I rearrange your mail and post bottom to enable others to have a look.
>
>>On Thu, Jul 28, 2011 at 4:30 AM, Christopher J. Ruwe =A0wrote:
>>> On Wed, 27 Jul 2011 10:49:42 +0800
>>> dave jones <s.dave.jones@gmail.com> wrote:
>>>
>>>> Hi,
>>>>
>>>> I cat get an IP address from dhcp server by adding the line
>>>> in /etc/rc.conf:
>>>>
>>>> ifconfig_em0=3D"DHCP"
>>>>
>>>> If I move my laptop to another place, I have to manually run
>>>> "dhclient em0" to get an IP. Otherwise, it won't get an IP
>>>> automatically.
>>>>
>>>> My question is it's possible to get ip address automatically from
>>>> different dhcp server? thanks.
>>>>
>>>> Regards,
>>>> Dave.
>>>> _______________________________________________
>>>> freebsd-questions@freebsd.org mailing list
>>>> http://lists.freebsd.org/mailman/listinfo/freebsd-questions
>>>> To unsubscribe, send any mail to
>>>> "freebsd-questions-unsubscribe@freebsd.org"
>>>
>>> Have a look at /etc/devd.conf. Mine include a portion
>>>
>>> #
>>> # Try to start dhclient on Ethernet like interfaces when the link comes
>>> # up. =A0Only devices that are configured to support DHCP will actually
>>> # run it. =A0No link down rule exists because dhclient automaticly exit=
s
>>> # when the link goes down.
>>> #
>>> notify 0 {
>>> =A0 =A0 =A0 =A0match "system" =A0 =A0 =A0 =A0 =A0"IFNET";
>>> =A0 =A0 =A0 =A0match "type" =A0 =A0 =A0 =A0 =A0 =A0"LINK_UP";
>>> =A0 =A0 =A0 =A0media-type =A0 =A0 =A0 =A0 =A0 =A0 =A0"ethernet";
>>> =A0 =A0 =A0 =A0action "/etc/rc.d/dhclient quietstart $subsystem";
>>> };
>>> #
>>> notify 0 {
>>> =A0 =A0 =A0 =A0match "system" =A0 =A0 =A0 =A0 =A0"IFNET";
>>> =A0 =A0 =A0 =A0match "type" =A0 =A0 =A0 =A0 =A0 =A0"LINK_DOWN";
>>> =A0 =A0 =A0 =A0media-type =A0 =A0 =A0 =A0 =A0 =A0 =A0"ethernet";
>>> =A0 =A0 =A0 =A0action "/etc/rc.d/dhclient quietstop $subsystem ; ifconf=
ig $subsystem inet 0.0.0.0";
>>> };
>>>
>>> I am under the impression that this rule does what you want to do.
>>>
>>> Cheers,
>>> --
>>> Christopher J. Ruwe
>>> TZ GMT + 2
>>>
>
>> Hi Christopher,
>>
>> Thanks for your solution. It does help a lot, but there's one problem.
>> For example, DHCP server is not started for some reason and my computer'=
s
>> ethernet cable is plugged. Once dhcp server started, I can't get the IP =
unless
>> I unplug and then plug the ethernet cable. Do you know how to solve
>> this issue? Thank you.
>>
>> Regards,
>> Dave.
>>
>
> Ok. To check whether I understand what you are saying: Your computer is r=
unning, but an external DHCP-server is not. Your computer tries to get an I=
P from the external DHCP server, which is down, so dhclient is unsuccessful=
. You then kick the DHCP-server back to live and then you have to plug in a=
nd out to get an IP?

Right. I'm sorry for the confusion.

> Assuming I understand correctly, that is exactly what should happen. You =
see, normally DHCP-servers don't flood the network with "Hello all dhclient=
s, I am dhcp-server, please tell me if you need an IP", usually the opposit=
e direction is in order as in "hello dhcp-server, I am dhclient, I need an =
IP, please give me one".
> You now have two options: 1) You coerce a manual request be running dhcli=
ent. 2) You plug in and out, which runs dhclient as you have configured to =
do so in your devd.conf.
> Of course you can set the retry-time for dhclient (see `man dhclient`) to=
 an absurldly low threshold, so you are saved doing the dhcp-discover-proce=
dure manually. It is, however, dubious, whether you want to do so. It might=
 be a smarter way to fix that DHCP-server of yours.

Thank you for the clear explanation. I will add "retry 10" in
dhclient.conf and give it a try.
I'm wondering if net/ifstated will work in this case. I'll give it a
shot as well.
Thanks again!

> Hope to have been of some help here,
> cheers
> --
> Christopher J. Ruwe
> TZ GMT + 2
>

Regards,
Dave.



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