CEF - Cisco Express Forwarding -Both routers and Layer 3 switch both have IOS routing software. -Software Routing is slow compared to ASICs L3 switching can use a software and hardware method to move data. FIB - Fowarding Information Base - Caches Routing Information from the Router supervisor ADJ Table "routes" (fowards) frames out a port based on mac address information. ASIC is a name for a switches hardware. CEF takes L3 routing informaion and caches it to the FIB. As the switch is booting up, it will look for all the next hop addresses in the routing table and pull the MAC addresses from the addresses. This information is then sent to the adjacency table with all the necessary ARP information. CEF only tracks routed ports (or interface vlans) Exceptions to CEF: Packets with Header options Packets with TTL expired Packets destined to use tunnel interfaces Packets with unsupported encapsulations Packets required fragmentaion (MTU Exceeded) ---------------------------------------- to turn on CEF: switch(config)#ip cef CEF has a feature to watch all traffic statistics. Will only work for routed interface vlans show ip cef vlan 200: shows what ips have been learned by CEF in vlan 200. ex output: switch#show ip cef vlan 151 192.168.0.0/24 attached to Vlan151 The 192.168.0.0/24 was learned on vlan 151 switch#show ip cef 192.168.0.25 192.168.0.25/32 receive show ip arp x.x.x.x shows arp information for the specified IP address, and what interface it was learned on.