AW: Re: howto disable default multiple device activation?

["netztier bluewin ch" <netztier bluewin ch>]

>Do you have any reasons to hate it, 

I for instance would - although much less on a unixoid OS than on *eew* Windoze. With multiple IP interfaces, there 
is a strong tendency for nonunicast IP packets leaving the box via the "wrong" interface - regardless of the source 
address being written into the packet. So in general, I would see use cases for not automatically having a wired and a 
wireless interfaces active at the same time. Some Laptop firmwares even have such a "Wifi XOR LAN" switch you can 
activate in their BIOSs.

>The fastest device is always used for new TCP connections, so it's not like it'll slow anything down.

How does TCP know about an interface's speed? I would assume that it just passes it's segments to the IP layer - 
which will then forward packets according to what the routing table says.

>Here's a specific example why it's good: I'm connected through my wifi
>device only and have a bunch of open TCP connections (ssh, irc, ...).
>Then I need to transfer a large file from the local network. I plug in
>the cable (to make it faster) and start the transfer. 

The way you describe it, it sounds like a small setup witha single router/firewall towards the internet, with some 
(file) server on your internal LAN. So both your WiFi and LAN NICs will probably have addresses from the same subnet 
and use the same router/firewall to reach non-local networks. As soon as your LAN NIC is up, the routing table gets 
modified to reach the local LAN via that interface and maybe another default route, pointing to the same 
router/firewall. Like this, TCP connections to the outside world will survive and not seem out-of-state to that 
firewall. 

But what happens to your routing table once you get DHCP lease and default route from a completely different LAN? 
Will the new default route take precedence over the existing one? How do you prevent problems if your now dual-homed 
hosts needs to talk to hosts beyond the respective local subnet - on both interfaces simultaneously?  


>My point is, there's simply no reason to deactivate the previously active device,

Yes. There are use cases where this is mandatory. As you pointed out - this needs to be taken care of by the 
administrator.

regards

Marc