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Behavior of globally defined static routes is different on each of the two CNA platforms.
If you declare a static route with the ip route command while in the top-level configuration mode (config) on a 5000 series device, the route will be automatically applied to the management module exclusively.
On a 3000 series device, however, the static route will be applied to both the management and engine modules, which are implemented on the same subsystem.
If the FastEthernet addresses assigned to both modules are in the same prefix, as in the following example (172.16.5.0/24), traffic from the engine module could be sent out through the management interface:
ip route 0.0.0.0 0.0.0.0 172.16.5.1 ! interface FastEthernet 0/0 description Management interface ip address 172.16.5.20 255.255.255.0 end ! interface FastEthernet 0/1 description Engine interface, same subnet ip address 172.16.5.21 255.255.255.0 end
If the FastEthernet address of the engine module is changed to a different prefix (172.16.6.0/24), as shown in the following configuration sample, responses to packets that were directed to the engine interface will be sent out through the management interface, resulting in an asymmetric routing path:
interface FastEthernet 0/1 description Engine interface, different subnet ip address 172.16.6.21 255.255.255.0 end
To avoid either of these conditions, define a static route on the interface assigned to the engine module:
interface FastEthernet 0/1 description Engine interface, with its own static route ip address 172.16.6.21 255.255.255.0 ip route 0.0.0.0 0.0.0.0 172.16.6.1 end
This will overrule the globally defined static route for engine module traffic.
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