[LARTC] Routing problem with 2 "wan" interfaces

[LARTC] Routing problem with 2 "wan" interfaces

[Michael Renner]

Hello!

I've got the following setup:

ippp0 (isdn), ppp0 (adsl), eth1 (internal lan), eth0 (nic dedicated to the
adsl modem)

Firewall rules:

Default 2.4. iptables (everything set to accept) except:
iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
iptables -t nat -A POSTROUTING -o ippp0 -j MASQUERADE


Routing Table:
Default gw is set to the ptp partner of ippp0


Problem:

Packets which are received on ppp0 don't get responded (tcpdump shows only
the incoming packets, no responses; stuff like ident lookups from irc
servers time out although a ident server is running and bound to 0.0.0.0)
Connections which get masqueraded through ppp0 with the following ruleset:

ip rule add from 192.168.0.10 to default iif eth1 table 50
ip route add table 50 via <ptp partner of ppp0>

work fine though.

If i switch the default gateway of the system from ippp0 to ppp0 i can
reach ppp0 from the outside w/o any problems, but ippp0 is unreachable.

ip_forward is enabled, rp_filter is disabled.


Do you need any additional information to help me on this?


best regards,
Michael Renner

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