Problem with access from remote system.

[Lauris Misa]

Hello!

I'm not really strong in fire walling and network things, maybe my 
problem is stupid. Any way it would be nice to have some suggestion how 
to resolve such situation ;)

I have system with two interfaces: eth0 is connected to internet, eth1 
is internal address. And virtual interface tun0 for VPN.

Everything works fine at least for two years till one moment when from 
one remote host (probably not only one but I have info about one) 
doesn't work anything. Including not restricted ICMP. When VERBOSE is 
switched on it logs such requests as MARTIAN.
But when I stop fiaif with "/etc/init.d/fiaif stop" everything works 
fine from that host too. After I start fiaif again everything stops. 
 From only that host. From everywhere else all allowed actions works fine.

I'm a bit confused with such situation.
I do not understand why exactly from that address is so and if there is 
something wrong with incoming packets then why it starts to work with 
fiaif not running?

Thanks,
BR
Lauris