How can I ensure outbound traffic uses the same interface as that of inbound traffic in Linux?

Question

I have a Linux box with two interfaces: one for data and the other for management purpose. If both are on the same network, I have a route added for both interfaces.

Imagine the routing table is:

192.168.132.0 255.255.255.0 eth0
192.168.132.0 255.255.255.0 eth1 ( management interface)

The problem is that even if a connection is initiated to mgmt IP (eth1), return traffic will be on eth0.

How can I ensure that return traffic on a connection uses the same interface as that of forwardeded traffic?

Answer 1

Ideally, both the interfaces should be part of differen IP subnets, but if you are convinced that you need to go this way only, then you should use linux split access routing.

Linux split access description

Split Access example from Novell

First, create two routing tables, T1 and T2 to be used for packets sent to or from these NICs by adding the lines

252 T1
251 T2

to /etc/iproute2/rt_tables.

Next, set up the routing rules to route incoming and outgoing packets via these tables:

ip route add 10.105.16.0/24 dev eth0 src 10.105.16.100 table T1
ip route add default via 10.105.16.2 dev eth0 src 10.105.16.100 table T1
ip rule add from 10.105.16.100 table T1

ip route add 10.105.16.0/24 dev eth1 src 10.105.16.101 table T2
ip route add default via 10.105.16.2 dev eth1 src 10.105.16.101 table T2
ip rule add from 10.105.16.101 table T2