4 receive 255.255.255.255/32 receive Usually, you won't need to look into what CEF is doing unless Cisco TAC tells you to. About the only time I've needed this command was when we had a CEF bug that caused packets to be sent out interfaces other than the ones indicated in the routing table. As a general rule, you should never disable CEF. Chapter 15: Switching Algorithms in Cisco Routers CHAPTER 16 Multilayer Switches Switches, in the traditional sense, operate at Layer 2 of the OSI stack. The first multi- layer switches were called Layer-3 switches because they added the capability to route between VLANs. These days, switches can do just about anything a router can do, including protocol testing and manipulation all the way up to Layer 7. Thus, we now refer to switches that operate above Layer 2 as multilayer switches. The core benefit of the multilayer switch is the capability to route between VLANs, which is made possible through the addition of virtual interfaces within the switch. These virtual interfaces are tied to VLANs, and are called switched virtual interfaces (SVIs). Figure 16-1 illustrates the principles behind routing within a switch. First, you assign ports to VLANs. Then, you create SVIs, which allow IP addresses to be assigned to the VLANs. The virtual interface becomes a virtual router interface, thus allowing the VLANs to be routed. Port 8 Port 9 Port 10 Port 11 Port 12 Port 13 Port 14 Port 15 VLAN 20 VLAN 30 VLAN 40 VLAN 10 VLAN 10 VLAN 20 Port 0 Port 1 Port 2 Port 3 Port 4 Port 5 Port 6 Port 7 Figure 16-1. VLANs routed from within a switch Most multilayer switches today do not have visible routers. The router is contained within the circuitry of the switch itself or in the supervisor (i.e., the CPU) of a modular switch. Older switch designs, like the Cisco 4000 chassis switch, have a Layer-3 module that was added to make the switch multilayer-capable. Such modules are no longer needed, since Layer-3 functionality is included with most supervisors. On chassis-based switches with older supervis