F

far-end alarm and control (FEAC)

Signal used to send alarm or status information from the far-end terminal back to the near-end terminal and to initiate loopbacks at the far-end terminal from the near-end terminal.

fast reroute

Mechanism for automatically rerouting traffic on an LSP if a node or link in an LSP fails, thus reducing the loss of packets traveling over the LSP.

field-replaceable unit (FRU)

Router component that customers can replace onsite.

firewall

A security gateway positioned between two different networks, usually between a trusted network and the Internet. A firewall ensures that all traffic that crosses it conforms to the organization’s security policy. Firewalls track and control communications, deciding whether to pass, reject, discard, encrypt, or log them. Firewalls also can be used to secure sensitive portions of a local network.

first in, first out (FIFO)

Queuing and buffering method where the first data packet stored in the queue is the first data packet removed from the queue. All JUNOS software interface queues operate in this mode by default.

flap damping

See damping.

flapping

See route flapping.

flexible PIC concentrator (FPC)

An interface concentrator on which PICs are mounted. An FPC inserts into a slot in a Juniper Networks router. See also physical interface card (PIC).

floating static route

A route that should be used only when all dynamically learned versions of that same route are no longer in the routing table.

flood and prune

Method of forwarding multicast data packets in a dense-mode network. This process repeats itself every 3 minutes.

flow control action

JUNOS software syntax used in a routing policy or a firewall filter. It alters the default logical processing of the policy or filter when a set of match conditions is met.

forwarding class

Internal router designation that represents the queuing service offered to IP packets matching some set of criteria. The forwarding class is assigned to a packet when it enters the router and can be modified by a routing policy or a firewall filter.

Forwarding Engine Board (FEB)

In M5 and M10 routers, provides route lookup, filtering, and switching to the destination port.

forwarding information base

See forwarding table.

forwarding table

JUNOS software forwarding information base (FIB). The JUNOS routing protocol process installs active routes from its routing tables into the Routing Engine forwarding table. The kernel copies this forwarding table into the Packet Forwarding Engine, which is responsible for determining which interface transmits the packets.

Frame Relay

Layer 2 encoding and addressing mechanism that uses a DLCI to segment logical circuits on a physical transmission media.

from

JUNOS software command syntax that contains match criteria in a routing policy or a firewall filter.

Full

OSPF adjacency state that represents a fully functional neighbor relationship.

fxp0

JUNOS software permanent interface used for out-of-band network access to the router.

fxp1

JUNOS software permanent interface used for communications between the Routing Engine and the Packet Forwarding Engine.

fxp2

JUNOS software permanent interface used for communications between the Routing Engine and the Packet Forwarding Engine. This interface is not present on all routers.