Hi,
There is an "anti-spoofing" issue that you haven't mentioned and may
well have to contend with. Some Linux distro's, certainly Redhat, when
installed with default settings will engage the anti-spoofing mechnism.
This prevents any interface from being used as a default route other
than the one declared in the routing table called "main".
You need to "echo 0 > /proc/sys/net/ipv4/conf/eth3/rp_filter" to turn
off the anti-spoofing for that interface.
Using iptables you can manually put back some of the anti-spoofing
mechanism. See "Rusty Russell's unreliable guide to iptables"
Regards Mike.
Paul Lewis wrote:
Hi,
Apologies for the cross-posting; I'm not sure whether this is a firewall or
routing issue, or both!
I have four network cards, detailed below. eth0 and eth3 connect to my ISPs,
and eth1 and eth2 connect to local networks. I want to route all traffic
from eth2 to eth0, and from eth1 to eth3. However, I am having a few
problems with this.
eth0
ip: 192.168.100.253/24
gw: 192.168.100.254 (ISP)
eth1
ip: 192.168.3.253/22
gw: 192.168.20.253 (eth3)
eth2
ip: 192.168.7.253/22
gw: 192.168.100.253 (eth0)
eth3
ip: 192.168.20.253/24
gw: 192.168.20.254 (ISP)
I have tried setting up routing using these commands:
echo "ISP_1" >> /etc/iproute2/rt_tables
echo "ISP_2" >> /etc/iproute2/rt_tables
ip route add 192.168.4.0/22 dev eth2 src 192.168.7.253 table ISP_1
ip route add default via 192.168.100.253 table ISP_1
ip route add 192.168.0.0/22 dev eth1 src 192.168.3.253 table ISP_2
ip route add default via 192.168.20.253 table ISP_2
ip rule add from 192.168.7.253 table ISP_1
ip rule add from 192.168.3.253 table ISP_2
However, this yielded no success. I have also tried a simple iptables
forwarding configuration (without the routing config above):
iptables -A FORWARD -i eth0 -o eth2 -j ACCEPT
iptables -A FORWARD -i eth2 -o eth0 -j ACCEPT
iptables -A FORWARD -i eth1 -o eth3 -j ACCEPT
iptables -A FORWARD -i eth3 -o eth1 -j ACCEPT
# default policy
iptables -P FORWARD DROP
Again, with no success. I do have a reasonably complex firewall in place,
but no other rules in the FORWARD section of the firewall. I have a number
of open ports under INPUT for other services the machine provides, and
nothing under OUTPUT.
In the NAT section, I have no rules in OUTPUT, a couple of MASQUERADING
rules under POSTROUTING, and hundreds of rules under PREROUTING (accepting
or denying machines based on their MAC).
I've had a few thoughts on this; do I need to have four default gateways
configured; one for each network card? And do I need more (or any)
forwarding rules in the firewall?
I've been struggling with this problem for some time now, and it's really
starting to annoy me. I would really appreciate any feedback people could
send me.
Many thanks,
Paul
---
Paul Lewis (paul.lewis@xxxxxxxxxxxxxxxxx)
Part II Student
Department Of Materials
University Of Oxford
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