Netfilter and multiple internet connections

["Jan" <Oblivion@tiscali.be>]

Hello,

I have a kernel 2.4.19 machine running netfilter (1.2.7a) and performing NAT
for my internal network.  The machine has two internet connections, one ADSL
and one via a cable provider.  I select the provider by changing the default
gateway at the netfilter machine.

The strange thing I noticed:  when I am using cable as the default gateway,
my firewall ruleset shows the multicast query the provider's router is
sending me on a regular base.  But when I change the default gateway to
direct all outgoing traffic via the ADSL link, there are no more log entries
showing the multicast query over the cable modem.

Although when I dump the packets on the cable interface, I do see the
Multicast queries.  The firewall ruleset stays the same.  I compared the
loaded version, only different in packet counters.

I suspect one of the kernel parameters (/proc/sys/net/...) influences this
behaviour.  But I don't know which one.
Or is this behaviour netfilter specific?
Do the packets which netfilter doesn't see get further into my machine?  Or
are they dropped by the kernel?

Thanks,
Jan