* 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] Thread overview: 6+ messages (download: mbox.gz follow: Atom feed -- 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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