l com- plain if you attempt to do SO: 2950(config-if)#duplex half Duplex can not be set until speed is set to non-auto value Additionally, gigabit switches may give you further warnings about trying to configure half duplex on gigabit ports: SW-3750(config-if)#duplex half % Duplex cannot be set to half when speed autonegotiation subset contains 1Gbps To set the speed of the interface, use the speed command. If the interface has previously been configured, you can return it to autonegotiation with the auto keyword: SW-3750(config-if)#speed Force 10 Mbps operation Force 100 Mbps operation Force 1000 Mbps operation auto Enable AUTO speed configuration Configuring Autonegotiation Once you've set the speed, you can set the duplex mode to auto, full, or half: SW-3750(config-if)#duplex ? auto Enable AUTO duplex configuration full Force full duplex operation half Force half-duplex operation On NX-OS, the commands are the same as the IOS equivalent: NX-5K(config)#int e1/5 NX-5K(config-if)#speed Force 10 Mbps operation Force 100 Mbps operation 1000 Force 1000 Mbps operation auto Enable AUTO speed configuration NX-5K(config-if)# NX-5K(config-if)#speed 1000 NX-5K(config-if)#duplex full Chapter 3: Autonegotiation CHAPTER 4 VLANs Virtual LANs, or VLANs, are virtual separations within a switch that provide distinct logical LANs that each behave as if they were configured on a separate physical switch. Before the introduction of VLANs, one switch could serve only one LAN. VLANs en- abled a single switch to serve multiple LANs. Assuming no vulnerabilities exist in the switch's operating system, there should be no way for a frame that originates on one VLAN to make its way to another. When I wrote the first edition of Network Warrior, I had not yet learned of VLAN-hopping exploits. There are ways to circumvent the VLAN barrier. Attacks such as switch spoofing and double tagging are methods used to gain access to one VLAN from another. Though reading data from another VLAN is not SO easy, denial-of-service attacks could be accompli