多网卡 A进A出，B进B出的解决方法

multi_networkcard.md

I have a Linux box running Ubuntu 10.04 with three interfaces: eth0, eth1 and eth2.

I am planning to use it as a WAN router for 4 public subnets assigned by two different ISP's.

Here are the subnets (I have converted the ISP assigned subnets to class C private subnets):

ISP 1   
WAN 192.168.0.176/30 gateway 192.168.0.177   
LAN 192.168.3.192/29

ISP 2   
WAN 192.168.6.208/30 gateway 192.168.6.209  
LAN 192.168.9.216/29

/30 subnets face respectives ISPs and /29 subnets face my LAN switch.

This is how IPs are assigned to the interfaces:

LAN interface 
eth0 192.168.3.193/29
eth0:0 192.168.9.217/29

ISP 1 interface
eth1 192.168.0.178/30

ISP 2 interface
eth2 192.168.6.210/30

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First, create a routing table for each ISP (only done once):

echo "11 isp1" >> /etc/iproute2/rt_tables
echo "12 isp2" >> /etc/iproute2/rt_tables

Then add a default route to each table pointing to the corresponding gateway:

ip route add default via 192.168.0.177 table isp1
ip route add default via 192.168.6.209 table isp2

Then add rules to send traffic to these tables based on the source address:

ip rule add from 192.168.3.192/29 table isp1
ip rule add from 192.168.0.176/30 table isp1
ip rule add from 192.168.9.216/29 table isp2
ip rule add from 192.168.6.208/30 table isp2