Re: understanding Routing Cisco vs. Linux
After reading the lot (not the configs: not accessibles)
if you say that there is a trunk between the 7200 (which does not
looks from the route definition you have), and is properly configured
(sub interfaces on the 7200 and same definition on the cat 5K RSM (if
you have one which i suppose as you say that you route trough the CAT)),
then you dont have any problems. (does't look properly coonfigured
if the 7200 send the traffic to the same interface).
There must be a proxy arp magic happening somewhere if you have another
router in the picture (please confirm that you have an RSM (route switch
module) in the cat or an attached router).
I'd configure it that way:
configure a VLAN on the RSM with a /30 network to connect to the 7200.
Make the 7200 route the network trough your address.
Manage you network per vlans ( and sub interfaces in your RSM config).
This idea to use a Linux box is interesting, but i dont think you'll get
better performances than trough the RSM + Layer3 swithing (which i suppose
is enabled), nor beeing easy to properly split your networks (as you have to separate
them to route trough your thing... Another point could be to bridge
and firewall, but i dunno if it is possible ..).