IP address assignment over two interfaces
adam at internode.com.au
Tue Oct 12 18:45:45 PDT 2004
I have two network interfaces in my laptop, rl0 and an0. rl0 is my onboard
Ethernet adapter and an0 is a Cisco wireless PCMCIA card.
When I'm at home, there are often times in which I may wish to switch from
wireless to wired for performance reasons when transferring files over my
LAN. Unfortunately the process to do this, as far as I know, is rather
My wireless network is configured with a WEP key and a passphrase. As a
result I have attempted to simplify my life by creating a script that I
execute when my system boots. It checks to see if my hard-wired ethernet
has an IP address, and if not, it grabs one via the wireless card (and sets
up the WEP key etc):
[adam at myhost /home/adam]$ cat /usr/local/bin/wireless
# Check to see if we have an Ethernet address on the physical port
if ifconfig rl0 | grep 0.0.0.0
ifconfig an0 wepmode on wepkey mywepkey ssid myssid
It kills dhclient, because I can't run two instances of it at once.
This works rather well at the moment, however if I want to switch back from
wireless to wired, I have to kill dhclient, config my wireless with
'ifconfig an0 0.0.0.0' and then re-run 'dhclient rl0'. That's really
What I'd like to accomplish is to be able to switch between these two cards
automatically. Preferably, I'd like to use wireless as a 'backup' to
wired, so that if I am hardwired in, wireless just shouldn't bother trying
to obtain an IP address. If I unplug my Ethernet connection, wireless
should sync up and take over operations.
I was inspired by OS/X's sweetness. It does exactly that; switches between
the two interfaces magically. I want some of that sweet stuff.
Any idea if the FreeBSD OS itself has any underlying capability for this
kind of thing (some sort of Interface watching daemon?) Also, if I
configured DHCP to assign the same IP address to both my wireless and wired
interfaces, that would possibly mean that any TCP sessions that I have open
will stay open, which is really, really cool.
Thanks for listening! :)
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