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[suse-security] another 3-interface firewall problem (two external, no DMZ)



Hi, 

I am running a small enterprise server under Suse 9.0.
The main tasks are: Masquerading an internal network, SMTP, POP3 and web
serving.

Everything works nice with two interfaces:
eth0: 1.2.3.4 netmask 255.255.255.192 (leased line with static IP)
eth1: 192.168.0.1 netmask 255.255.255.0 (internal network)
with default route 1.2.3.3
Web server is listening on 1.2.3.4, SMTP on both interfaces, POP3 only at
the internal interface

NOW: to keep traffic costs as low as possible, we like to route the main
traffic over a DSL flat rate.
Configuring the DSL stuff gives the aditional ppp0 interface (PPPoE with
eth2), masquerading works and I can see the web server at 1.2.3.4 due to the
additional entry:
iptables -A INPUT -i eth1 -s 192.168.0.0/24 -d 1.2.3.4 -j ACCEPT

BUT: The address 1.2.3.4 is not responding from the outside any more.
Both eth0 and ppp0 are configured as external interfaces in the SuSEfirewall
configuration.

I think, the problem can be seen as a sort of load balancing for the leaving
IP packets.

Any hints, how to get the official external IP address working again ?


Best regards
    Peter


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