or modules, the router is a separate de- vice with its own operating system. The router in these switches is a daughter card on the supervisor called the multilayer switch function card (MSFC). On these devices, Layer-2 operations are controlled by the CatOS operating system, while Layer-3 routing operations are controlled by the IOS operating system. This configuration, called hybrid mode, can be a bit confusing at first. To some people, having a separate os for each function makes more sense than combining them. For most people, however, the single-OS model-called native mode on the chassis switches-is probably easier. Nexus switches run NX-OS, which is similar to IOS. On a chassis-based switch in hybrid mode, physical interfaces and VLANs must be configured in CatOS. To route between them, you must move to IOS and create the SVIs for the VLANs you created in CatOS. Another option for some switches is to change a switch port into a router port-that is, to make a port directly addressable with a Layer-3 protocol such as IP. To do this, you must have a switch that is natively IOS or running in IOS native mode. Nexus 7000 switch ports default to router mode. Sometimes, I need to put a Layer-3 link between two multilayer switches. Configuring a port, a VLAN, and an SVI involves a lot of steps, especially when you consider that the VLAN will never have any ports included aside from the interswitch link. In such cases, converting a switch port to a router port is simpler. You cannot assign an IP address to a physical interface when it is configured as a switch port (the default state for most Catalyst switches): 3750-I0S(config)#int g1/0/17 3750-I0S(config-if)#ip address 10.10.10.1 255.255.255.0 % Invalid input detected at '^' marker. To convert a multilayer switch port to a router port, configure the port with the com- mand no switchport: 3750-I0S(config)#int g1/0/17 3750-I0S(config-if)#no switchport Once you've done this, you can assign an IP address to the physical interface: 3750-I0S(config)#int g1/0/17 3750-I0S(