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Chapter 6 Configuring the Internet Protocol
Configuring IP Opportunistic Layer 3 Forwarding
6-12
Cisco Content Services Switch Routing and Bridging Configuration Guide
OL-8241-02
Using opportunistic Layer 3 forwarding, the CSS inspects the IP packet header to
determine the destination IP address. Instead of forwarding the packet to Router1,
the CSS forwards the packet directly to End Station B. Because the CSS handles
the packet only once, the router and uplink are not used and network resources are
conserved.
The options for this global configuration mode command are as follows:
• local (default) - Applies opportunistic Layer 3 forwarding if the destination
IP address belongs to a node that resides on one of the subnets directly
attached to the CSS and the CSS is aware of an ARP resolution for that node.
Because the local option is the default, use the no ip opportunistic command
to reconfigure IP opportunistic Layer 3 forwarding to the local setting.
• all - Applies opportunistic Layer 3 forwarding if the destination IP address
matches any entry in the CSS routing table. We do not recommend this option
if the topology includes multiple routers and the CSS does not know all of the
routes the routers are aware of.
• disabled - The CSS does not perform opportunistic Layer 3 forwarding.
Regular Layer 3 forwarding is performed only for packets that contain the
CSS destination MAC address.
For example, to configure IP opportunistic Layer 3 forwarding to all, enter:
(config)# ip opportunistic all
To reconfigure IP opportunistic Layer 3 forwarding to the default of local enter:
(config)# no ip opportunistic
When you configure ip opportunistic all, you can use the ip route
originated-packets command (see the “IP Configuration Quick Start” section) to
configure routes that the CSS uses to reach devices, but does not use as
opportunistic routes for forwarding traffic. Routes created using the ip route
originated-packets command apply only to packets that originate on the CSS.
Packets and flows forwarded by the CSS do not use these routes.
For example:
(config)# ip route 0.0.0.0 /0 192.168.1.7 originated-packets