270-272 FIFO (first in, first out), 576, 610 Nexus 5000 devices, 15 Firewall Services Modules (see FWSMs) fabric ports, 271 firewalls, 459 failover (see also ASAs; PIX firewalls) ASA appliances and, 490-501 alternate designs, 465-466 common terminology, 491 best practices, 459-461 configuring active/active, 497-501 DMZ and, 461 configuring active/standby, 494-496 dynamic routing and, 148 functionality, 492-493 functionality, 459 monitoring status, 496 GRE and, 179 NTP considerations, 691 transparent mode, 470, 493 testing considerations, 700 first hop redundancy failover active command, 497, 499 GLBP and, 189-196 failover command, 494 HSRP and, 181-184 failover group group# command, 499 HSRP interface tracking, 184-186 failover lan interface command, 495 Nexus and HSRP, 189 failover lan unit primary command, 491 two-link failover scenario, 186-188 failures first in, first out (FIFO), 576, 610 disaster chains and, 699 fixed-configuration switches, 14 human error and, 697 flex links, 324 multiple components, 698 FlexWAN (WAN modules), 15, 249 no failover testing, 700 Index floating static route, 119 full-duplex, 355 Foreign Exchange Office (FXO), 528 (see also T1) Foreign eXchange Service modules, 249 autonegotiation failure and, 21 Foreign Exchange Station (FXS), 528 duplex mismatch problem, 101 forward-digits command, 552 functionality, 19 Forward-Explicit Congestion Notification fully meshed networks, 391 (FECN), 395 fully qualified domain name (FQDN), 638 forwarders, defined, 190 FWSMs (Firewall Services Modules) forwarding state, 91 about, 15, 231, 244 forwarding table, 215 availability of, 469 FQDN (fully qualified domain name), 638 network design considerations, 642 frame check sequence (FCS), 39 FXO (Foreign Exchange Office), 528 Frame Relay FXS (Foreign Exchange Station), 528 benefits of, 389 configuring, 389, 396-403 congestion avoidance, 395 G.711 CODEC standard, 526, 554, 562 functionality, 387-390 inverse ARP and, 389, 399 G.722 CODEC standard, 526 Local Management Interface and, 394-395 G.729 CODEC st