ESF (Extended Super Frame), 360 EtherChannel Dual-Tone Multifrequency (DTMF) Relay, configuring, 68-75 cross-stack, 75 duplex command, 23 FEX considerations, 290 duplex modes flex links and, 324 autonegotiation failure and, 21 configuring parameter, 23 functionality, 63 defined, 19 load balancing, 64-68 duplex mismatch problem, 100 managing, 68-75 Multichassis EtherChannel, 75 Ethernet support levels, 20 dynamic secure MAC addresses, 329 network design considerations, 642 Dynamic Trunking Protocol (DTP), 40 protocols supported, 68 virtual Port-Channel, 75-80, 297 Index VSL support, 256 troubleshooting, 700-704 VSS support, 240 far-end alarm and control (FEAC), 378 Ethernet frames, 11 far-end block errors (FEBEs), 377, 381 Ethernet handoffs, 598-602 far-end out-of-frame (FEOOF), 377 Ethernet modules, 244 Fast EtherChannel (see EtherChannel) Ethernet network segments, 7 fast switching Ethernet networks configuring switching paths, 218 ARP support, 389 functionality, 211-213 broadcast domains, 8 managing switching paths, 218 collision domains, 8 FCS (frame check sequence), 39 hubs and, 5-10 FEAC (far-end alarm and control), 378 switches and, 10-18 feature command, 274 Ethernet Out-of-Band Channel (EOBC), 234 feature glbp command, 192 Ethernet switches, 10 feature hsrp command, 189 ETRN deque command (SMTP), 478 feature interface-vlan command, 224, 228, exclude command (NX-OS), 278 express forwarding packets, 152 feature tacacs+ command, 451 Extended Super Frame (ESF), 360 feature vpc command, 76 Extensible Authentication Protocol (EAP), 514 FEBEs (far-end block errors), 377, 381 Exterior Gateway Protocol (EGP), 107, 126 FEC (Fast EtherChannel) (see EtherChannel) external gateway protocols, 127 FECN (Forward-Explicit Congestion Extreme Errored Seconds counter, 363 Notification), 395 FEOOF (far-end out-of-frame), 377 fex associate command, 292 FEXs (Fabric Extenders) fabric bus, 233 configuring, 290-294 Fabric Extenders (FEXs) Nexus 2000 devices, 270-272 configuring, 290-294 Nexus 5000 devices, 15 Nexus 2000 devices, 