Re: Possible a better order to switch connections

[Karl Hegbloom <hegbloom pdx edu>]

On Sun, 2005-10-02 at 15:43 +0300, Paul Ionescu wrote:
> IMHO, a better approach is to let the old connection running, configure
> the new connection, switch to the new connection, (optionally notify all
> apps that there was a net change), and deactivate the old connection.
> 
> This way, there is no net downtime, and I don't think there is a major
> impact in NM.

The "downtime" is brief, and the new interface cannot have the same IP
as the old one if you don't bring the old one down first.  Open TCP
"stream" network connections will stop working when you bring down the
interface they are routed over, since their IP goes away.  For
"connectionless" UDP, that's probably not a problem, unless the
application layer keeps track of your IP address and something happens
when that changes.

Question: 

If, for instance, the wired connection is brought down, and then the
wifi is  brought up right away and given the same IP that the wired
interface just had, will open TCP connections continue to function?
That is to say, will the Linux networking code move the connection to
the new interface?

What if there was a configuration option (perhaps a default) to have it
move the old IP over to the new interface, as a secondary IP, provided
the network and mask are the same?  Given that, what if there was a way
to flag it to be automatically deleted once all active connections on it
are gone?  Should that be in-kernel, or something NetworkManager does?

It seems to me that this is probably possible and a use-case that may
well have been considered during the design and implementation of the
Linux networking stack.  Am I correct?

-- 
Karl Hegbloom <hegbloom pdx edu>