Fwd: Rapid DHCP

[Chuck Anderson]

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.

>   http://code.google.com/p/android/issues/detail?id=11236

This was a case of a client continuing to use an IP address /after it
had expired/.  This is clearly broken behavior.

> > Of course, none of this helps if your DHCP leases are short, but it
> > certainly helps if you put your laptop to sleep a lot and wake it up in
> > the same location.
> > 
> 
>  I tend to wake mine up in new locations a lot ... NM doesn't seem to
> take very long to latch onto the new one.

Most of the problems I have after resume are with flakey wireless
drivers and/or wpa_supplicant making a solid association to an AP
before even getting to the DHCP stage.