* Handling of multiple DHCP OFFERs
@ 2011-10-03 23:18 John Musbach
2011-10-03 23:21 ` David Miller
0 siblings, 1 reply; 6+ messages in thread
From: John Musbach @ 2011-10-03 23:18 UTC (permalink / raw)
To: linux-kernel
Hello, I am configuring a network that'll have multiple DHCP servers
and I was wondering how Linux handles receiving multiple DHCP OFFERs?
More specifically, how does it choose which one to prefer and how long
will it wait for a answer from a preferred server if the other server
answers first? Thanks.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Handling of multiple DHCP OFFERs
2011-10-03 23:18 Handling of multiple DHCP OFFERs John Musbach
@ 2011-10-03 23:21 ` David Miller
2011-10-03 23:36 ` Chris Friesen
0 siblings, 1 reply; 6+ messages in thread
From: David Miller @ 2011-10-03 23:21 UTC (permalink / raw)
To: johnmusbach1; +Cc: linux-kernel
From: John Musbach <johnmusbach1@gmail.com>
Date: Mon, 3 Oct 2011 23:18:06 +0000 (UTC)
> Hello, I am configuring a network that'll have multiple DHCP servers
> and I was wondering how Linux handles receiving multiple DHCP OFFERs?
> More specifically, how does it choose which one to prefer and how long
> will it wait for a answer from a preferred server if the other server
> answers first? Thanks.
There are multiple userspace implementations of DHCP, and the kernel
does not usually get involved at all. You'll therefore have to ask
the folks who write and maintain the various DHCP implementations.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Handling of multiple DHCP OFFERs
2011-10-03 23:21 ` David Miller
@ 2011-10-03 23:36 ` Chris Friesen
2011-10-04 1:12 ` Robert Hancock
0 siblings, 1 reply; 6+ messages in thread
From: Chris Friesen @ 2011-10-03 23:36 UTC (permalink / raw)
To: David Miller; +Cc: johnmusbach1, linux-kernel
On 10/03/2011 05:21 PM, David Miller wrote:
> From: John Musbach<johnmusbach1@gmail.com>
> Date: Mon, 3 Oct 2011 23:18:06 +0000 (UTC)
>
>> Hello, I am configuring a network that'll have multiple DHCP servers
>> and I was wondering how Linux handles receiving multiple DHCP OFFERs?
>> More specifically, how does it choose which one to prefer and how long
>> will it wait for a answer from a preferred server if the other server
>> answers first? Thanks.
>
> There are multiple userspace implementations of DHCP, and the kernel
> does not usually get involved at all. You'll therefore have to ask
> the folks who write and maintain the various DHCP implementations.
What about netbooting? Or are you expecting people to use initramfs
with a userspace implementation?
Chris
--
Chris Friesen
Software Developer
GENBAND
chris.friesen@genband.com
www.genband.com
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Handling of multiple DHCP OFFERs
2011-10-03 23:36 ` Chris Friesen
@ 2011-10-04 1:12 ` Robert Hancock
2011-10-04 8:03 ` Bernd Petrovitsch
2011-10-04 14:31 ` Chris Friesen
0 siblings, 2 replies; 6+ messages in thread
From: Robert Hancock @ 2011-10-04 1:12 UTC (permalink / raw)
To: Chris Friesen; +Cc: David Miller, johnmusbach1, linux-kernel
On 10/03/2011 05:36 PM, Chris Friesen wrote:
> On 10/03/2011 05:21 PM, David Miller wrote:
>> From: John Musbach<johnmusbach1@gmail.com>
>> Date: Mon, 3 Oct 2011 23:18:06 +0000 (UTC)
>>
>>> Hello, I am configuring a network that'll have multiple DHCP servers
>>> and I was wondering how Linux handles receiving multiple DHCP OFFERs?
>>> More specifically, how does it choose which one to prefer and how long
>>> will it wait for a answer from a preferred server if the other server
>>> answers first? Thanks.
>>
>> There are multiple userspace implementations of DHCP, and the kernel
>> does not usually get involved at all. You'll therefore have to ask
>> the folks who write and maintain the various DHCP implementations.
>
> What about netbooting? Or are you expecting people to use initramfs with
> a userspace implementation?
>
> Chris
>
Normally with PXE boot it's the PXE ROM that initially gets the IP
address. After the kernel boots up, userspace normally repeats the process.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Handling of multiple DHCP OFFERs
2011-10-04 1:12 ` Robert Hancock
@ 2011-10-04 8:03 ` Bernd Petrovitsch
2011-10-04 14:31 ` Chris Friesen
1 sibling, 0 replies; 6+ messages in thread
From: Bernd Petrovitsch @ 2011-10-04 8:03 UTC (permalink / raw)
To: johnmusbach1; +Cc: Chris Friesen, David Miller, linux-kernel, Robert Hancock
On Mon, 2011-10-03 at 19:12 -0600, Robert Hancock wrote:
> On 10/03/2011 05:36 PM, Chris Friesen wrote:
> > On 10/03/2011 05:21 PM, David Miller wrote:
> >> From: John Musbach<johnmusbach1@gmail.com>
> >> Date: Mon, 3 Oct 2011 23:18:06 +0000 (UTC)
> >>
> >>> Hello, I am configuring a network that'll have multiple DHCP servers
> >>> and I was wondering how Linux handles receiving multiple DHCP OFFERs?
Define "Linux":
The kernel?
- A given distribution?
- All distributions?
- The major ones?
- ISCs dhclient?
- RedHats "pump"?
- Other DHCP clients?
> >>> More specifically, how does it choose which one to prefer and how long
> >>> will it wait for a answer from a preferred server if the other server
> >>> answers first? Thanks.
IMHO it doesn't really work in general to have multiple (standalone)
DHCP servers in one network.
Perhaps/probably it works if there is no absolutely dynamical allocation
from pools but only static ones which are identical across all DHCP
servers (as some kind of high-availability).
> >> There are multiple userspace implementations of DHCP, and the kernel
> >> does not usually get involved at all. You'll therefore have to ask
> >> the folks who write and maintain the various DHCP implementations.
> >
> > What about netbooting? Or are you expecting people to use initramfs with
> > a userspace implementation?
>
> Normally with PXE boot it's the PXE ROM that initially gets the IP
> address. After the kernel boots up, userspace normally repeats the process.
I would assume that PXE ROMs also take the first received DHCPOFFER and
use it.
>From DHCPs point of view, it is the clients decision which DHCPOFFER it
honors or chooses to ignore (and the servers decision it it actually
sends an DHCPOFFER).
In reality (and e.g. for ISCs dhclient), usually the first received one
will be used (because it's the easiest to implement, it avoids the
problems with deciding how long to wait, takes less time on bootup
because there is no unnecessary timeout!) and last time I looked into it
(which was quite time ago ...), there was no feature to filter or
(securely) authenticate anything (which would actually make sense as the
client could detect invalid DCHP offers from rogue DHCP servers. Lots of
devices have such a beast on board nowadays and I wouldn't bet that all
of them are deactivated per default).
Bernd
--
Bernd Petrovitsch Email : bernd@petrovitsch.priv.at
LUGA : http://www.luga.at
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Handling of multiple DHCP OFFERs
2011-10-04 1:12 ` Robert Hancock
2011-10-04 8:03 ` Bernd Petrovitsch
@ 2011-10-04 14:31 ` Chris Friesen
1 sibling, 0 replies; 6+ messages in thread
From: Chris Friesen @ 2011-10-04 14:31 UTC (permalink / raw)
To: Robert Hancock; +Cc: David Miller, johnmusbach1, linux-kernel
On 10/03/2011 07:12 PM, Robert Hancock wrote:
> On 10/03/2011 05:36 PM, Chris Friesen wrote:
>> On 10/03/2011 05:21 PM, David Miller wrote:
>>> There are multiple userspace implementations of DHCP, and the kernel
>>> does not usually get involved at all. You'll therefore have to ask
>>> the folks who write and maintain the various DHCP implementations.
>>
>> What about netbooting? Or are you expecting people to use initramfs with
>> a userspace implementation?
>
> Normally with PXE boot it's the PXE ROM that initially gets the IP
> address. After the kernel boots up, userspace normally repeats the process.
I've worked with quite a few boards where PXE boots the kernel, but the
kernel needs to do DHCP to get the location of the root filesystem (as
well as various DHCP options not understood by PXE).
Chris
--
Chris Friesen
Software Developer
GENBAND
chris.friesen@genband.com
www.genband.com
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2011-10-04 14:33 UTC | newest]
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-- links below jump to the message on this page --
2011-10-03 23:18 Handling of multiple DHCP OFFERs John Musbach
2011-10-03 23:21 ` David Miller
2011-10-03 23:36 ` Chris Friesen
2011-10-04 1:12 ` Robert Hancock
2011-10-04 8:03 ` Bernd Petrovitsch
2011-10-04 14:31 ` Chris Friesen
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