Fast interrupts Fast Path Feature freeze fib_info structure fib_lookup() fib_node structure fib_rule structure fib_select_default() fib_select_multipath() fib_table structure fib_validate_source() File systems 2nd File Transfer Protocol (FTP) defined Filters change() function classify() function delete() function destroy() function dump() function get() function init() function put() function walk() function find_proto() fini Finite state machine (FSM) Firewalls: application gateways (proxies) functional principle of limits of the firewall principle packet filters protocol-specific particularities quality of a packet-filter architecture Firmware Flags, IP packet header Flooding fn_zone structure Forward chain 2nd Forward delay timer Forward-delay timer Forwarding database Forwarding functions: bridges: br_fdb_get() br_flood() br_forward() br_handle_frame() br_pass_frame_up() Forwarding packets ip6_forward() ip6_forward_finish() Forwarding procedure: IP routing files in the proc file system longest prefix routing table Forwarding process: IP routing ip_route_input() ip_route_input_slow() ip_route_output() ip_route_output_key() ip_route_output_slow() Fragment ID field, IP packet header Fragment Offset field, IP packet header Fragmenting Fragments Frame Check Sequence (FCS) 2nd Frame synchronization Free Software Foundation, GNU project free_dma() free_irq() FreeS/WAN