Re: How to obtain an IP-address immediately
- From: Lew Pitcher <lpitcher@xxxxxxxxxxxx>
- Date: Wed, 18 Jul 2007 07:42:16 -0700
On Jul 13, 3:15 pm, Johann Höchtl <jane...@xxxxxxxxx> wrote:
Hello everybody,
first I am sorry, that this is going to be one of those "In Windows it
works, but not on Linux"
I use Kubuntu with kernel 2.6.15-28-386 on a Laptop. Sometimes I am
connected wired, sometimes wireless.
On Windows the OS detects whenever i attach a wired connection an will
obtain an IP-Adress _immediately_. Good.
In Ubuntu it takes some time ... sometimes it's fasters, sometimes
slower. Seems to be some dhcp-renew mechanism. Whatever.
In fact it should _detect_ when a cable get's attached. Is this known
behaviour, some poor hardware integration in whatever shell script or
should i upgrade my Kubunu and it will automagically work?
In this case, I believe that it is Windows that is broken, and not
Linux.
In my experience, Windows violates the DHCP protocol requirements by
using the last assigned IP address on restart, rather than querying
for a DHCP renewal of the address. In this way, Windows can access the
network faster because it doesn't have to wait for the completion of
DHCP address negotiations.
The problem is that (IIRC) this procedure is a violation (or at least
a violent bending) of the DHCP protocol. Basically, once the client
disconnects, or when the lease expires, the DHCP server can reassign
the IP address as it sees fit, and it is only when the DHCP Renew
request is sent that the (previously disconnected and reconnected)
client will find out that the address is no longer available.
Windows DHCP client presumes that it will always be connected to the
same network, and that the DHCP server won't normally reassign the IP
address. Linux DHCP client(s), on the other hand, follow the DHCP
protocol, and immediately request a Renewal on startup. Of course,
this takes a bit of time to complete, so Linux DHCP looks slower than
Windows DHCP.
Of course, you can break Linux DHCP so that it works the same way as
Windows DHCP does. All you need to do is change the code and recompile
(or get someone else to do that for you).
HTH
--
Lew
.
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