Routing not working

[Dan Track]

Hi,

I've got a server where I've got two interfaces (vlan 200 and vlan
300). If I get traffic coming into vlan 200 but sourced from a network
that vlan 200 subnet doesn't know about, the server should send the
traffic out of it's default gateway i.e. vlan 300, but this isn't
happening. If I do a tcpdump on both interfaces I can see traffic
coming in on vlan 200 but failing to even be present on the return in
vlan 300 (not even present on vlan 200 - did it for sanity sake).
However, if I put in an explicit route in stating that this unknown
network exists out of vlan 200 then everything works fine.

My routing table is like this:

ip route
166.14.134.144/28 dev vlan200  proto kernel  scope link  src 166.14.134.154
159.156.137.32/28 dev vlan300  proto kernel  scope link  src 159.156.137.42
127.0.0.0/8 dev lo  scope link
default via 159.156.137.33 dev vlan300

vlan 200 and vlan 300 sit on the same bonded interface. Trunking is
set on the switch.

It's almost as though the OS (kernel) is saying that you can't take
input from one int and then send it out another int. Are there some
parameters I need to change?

Thanks for any help.

Dan