This is strange. Take my laptop, RH9, with eth0 say 192.168.1.100
and wlan0 say 192.168.1.101. The eth0 is not plugged in. However, from my
server I can ping 192.168.1.100 and the first hit takes 30 to 100ms and the
second and thereafter take 2ms ... but the eth0 is not plugged in so ping
should fail - really. Then if I plug in eth0 and ping again it actually
takes about 1ms or so, a lot faster. Then I unplug the eth0 again and try
pinging 192.168.1.100 again and it fails .... this behaviour is consistent
after every reboot. /sbin/arp on the server confirms that wlan0 answers the
ping for the .100 address. I have the masks set to 255.255.255.0 for all.

So how do I avoid the initial "incorrect behaviour". My wlan0 driver is
hostap, could it be that the redhat network scripts don't like the wlan0
id? SHould I have a go with the iptables on my laptop perhaps ..

Hendrik

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Hendrik-Jan Agterkamp wrote:
quote:

> This is strange. Take my laptop, RH9, with eth0 say 192.168.1.100
> and wlan0 say 192.168.1.101. The eth0 is not plugged in. However, from my
> server I can ping 192.168.1.100 and the first hit takes 30 to 100ms and
> the second and thereafter take 2ms ... but the eth0 is not plugged in so
> ping should fail - really. Then if I plug in eth0 and ping again it
> actually takes about 1ms or so, a lot faster. Then I unplug the eth0 again
> and try pinging 192.168.1.100 again and it fails .... this behaviour is
> consistent after every reboot. /sbin/arp on the server confirms that wlan0
> answers the ping for the .100 address. I have the masks set to
> 255.255.255.0 for all.
>
> So how do I avoid the initial "incorrect behaviour". My wlan0 driver is
> hostap, could it be that the redhat network scripts don't like the wlan0
> id? SHould I have a go with the iptables on my laptop perhaps ..


Cool, answer to myself ;-)

On the laptop I do

/sbin/iptables --flush
/sbin/iptables -A INPUT -i wlan0 -d ! 192.168.1.101 -j DROP
/sbin/iptables -A INPUT -i wlan0 -d 192.168.1.101 -j ACCEPT
/sbin/iptables -A INPUT -i eth0 -d ! 192.168.1.100 -j DROP
/sbin/iptables -A INPUT -i eth0 -d 192.168.1.100 -j ACCEPT

which has the desired effect but one problem remaining.
With eth0 unplugged, server's arp cache pick's up the wrong
hwaddr when I ping the .100 address on the server. A remedy
to that is to do on the server

/sbin/arp -d laptop-eth0

or on the laptop do

ping -I eth0 -c 1 server

The latter is nice, but how to automate it, not using cron?

Almost happy
Hendrik

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