Fwd: Rapid DHCP

Richard W.M. Jones rjones at redhat.com
Sun Jul 31 20:35:15 UTC 2011

On Sun, Jul 31, 2011 at 12:35:29AM -0400, Chuck Anderson wrote:
> On Sat, Jul 30, 2011 at 11:30:30PM -0400, Genes MailLists wrote:
> > On 07/30/2011 06:49 PM, Dan Williams wrote:
> > > What's unique about the method described there is that the Mac
> > > configures the interface with the same IP address it previously had if
> > > the lease is still valid, while NetworkManager waits for the DHCP server
> > > confirm the lease.  So we could presumptuously configure the interface
> > > with the previous address from the lease and then only tear it down if
> > > the DHCP server fails or rejects the renewal.
> > 
> >   Probably best not to do this - as it can lead to duplicate IP's on the
> > network - even if briefly - wasn't something like this an issue with
> > some smartphones and princeton univ wifi - and led to them banning
> > android for whatever version had the problem ?
> No, it cannot lead to duplicate IPs *if the lease is still valid*.  If
> the client has a cached lease, and the lease has not yet reached
> expiry, then the promise that the DHCP server has made to that client
> for it to use that IP address for that period of time is still valid
> and the client is free to continue use that IP address.

Most (broken) domestic routers forget the DHCP leases they gave out
after being rebooted.


Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-p2v converts physical machines to virtual machines.  Boot with a
live CD or over the network (PXE) and turn machines into Xen guests.

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