Software makes me sad sometimes.
Every time the iwlagn driver crashes and has to be reloaded (and it does that distressingly often, since it doesn't seem to reset the device and recover when its closed-source firmware crashes), NetworkManager kills the connection and restarts completely. Not unreasonably, I suppose.
But then, all NFS mounts get automatically unmounted, which is a complete pain in the arse.
And my VPN connection is reset, and because Cisco are stupid I don't get the same VPN IP address next time I connect, even if it is still available. (I think I ought to be able to work around this from the client side, if I don't mind storing the authentication cookie on the client machine.).
Although having said that, the main reason I'd want my IP address to remain the same is so that my connection to the mail server can persist and I don't have to wait through Evolution's painfully slow startup.
Unfortunately, Evolution also responds to the network offline/online events by reporting -EAGAIN errors all the time when it auto-saves emails that you're composing, and stops being able to display mail folders — the index just comes up empty. So it needs to be killed and restarted too. (This has been in bugzilla since November last year).