LARTC - Sep 2006 - How to use different path for INCOME and OUTGOING package ?

there are 3 computers.

A-------------B--------------C

I want the outgoing packages of B go to C.
And receive responding package from A.

As soon as insert the routing entry:
ip route add 10.0.0.0/8 via C src B dev BC

B seems stop receiving packages from A.
Use tcpdump on B, I can get the package.
But, it seems that kernel check the routing table, and found that the 
source address of the package coming form A is not in routing table of B 
to A, actually, it is in the table of B to C,
then the package is dropped.

How to configure the kernel not to drop the package ?

I got it.
I have mistakenly enabled rp_filter.