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Forwarding information base
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Forwarding information base
A forwarding information base (FIB), also known as a forwarding table or MAC (address) table, is most commonly used in network bridging, routing, and similar functions to find the proper output network interface controller to which the input interface should forward a packet. It is a dynamic table that maps MAC addresses to ports. It is the essential mechanism that separates network switches from Ethernet hubs. Content-addressable memory (CAM) is typically used to efficiently implement the FIB, thus it is sometimes called a CAM table.
At the data link layer, a FIB is most notably used to facilitate Ethernet bridging based on MAC addresses. Other data-link-layer technologies using FIBs include Frame Relay, Asynchronous Transfer Mode (ATM) and Multiprotocol Label Switching (MPLS).
The role of an Ethernet switch is to forward Ethernet frames from one port to another. The presence of a FIB is one attribute that separates a switch from a hub. Without a functional FIB, all frames received by a network switch would be echoed back out to all other ports, much like an Ethernet hub. In bridging packets between ports, a switch should only emit a frame on the port where the destination network device resides (unicast), unless the frame is for all nodes on the switch (broadcast), multiple nodes (multicast) or if the switch doesn't know where the destination device resides (unicast flood).
Switches learn the port on which they first saw a particular source address and associate that port with that address. When the bridge subsequently receives a frame with a destination address in its FIB, it sends the frame out the port stored in the FIB entry.
The FIB is a memory construct used by Ethernet switch to map a station's MAC address to the switch port the station is connected to. This allows switches to facilitate communications between connected stations at high speed.
While the exact mechanics of a forwarding table is implementation-specific, the general model for Frame Relay is that switches have statically defined forwarding tables, one per interface. When a frame with a given data link connection identifier (DLCI) is received on one interface, the table associated with that interface gives the outgoing interface, and the new DLCI to insert into the frame's address field.
ATM switches have link-level forwarding tables much like those used in Frame Relay. Rather than a DLCI, however, interfaces have forwarding tables that specify the outgoing interface by virtual path identifier (VPI) and virtual circuit identifier (VCI). These tables may be configured statically, or they can be distributed by the Private Network-to-Network Interface (PNNI) protocol. When PNNI is in use, the ATM switches at the edges of the network map one of the standard ATM end-to-end identifiers, such as an NSAP address, to the next-hop VPI/VCI.
MPLS has many similarities, at the forwarding level, to ATM. The label edge routers at the edges of an MPLS cloud map between the end-to-end identifier, such as an IP address, and a link-local label. At each MPLS hop, there is a forwarding table that tells the label-switched router which outgoing interface is to receive the MPLS packet, and what label to use when sending the packet out that interface.
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Forwarding information base AI simulator
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Forwarding information base
A forwarding information base (FIB), also known as a forwarding table or MAC (address) table, is most commonly used in network bridging, routing, and similar functions to find the proper output network interface controller to which the input interface should forward a packet. It is a dynamic table that maps MAC addresses to ports. It is the essential mechanism that separates network switches from Ethernet hubs. Content-addressable memory (CAM) is typically used to efficiently implement the FIB, thus it is sometimes called a CAM table.
At the data link layer, a FIB is most notably used to facilitate Ethernet bridging based on MAC addresses. Other data-link-layer technologies using FIBs include Frame Relay, Asynchronous Transfer Mode (ATM) and Multiprotocol Label Switching (MPLS).
The role of an Ethernet switch is to forward Ethernet frames from one port to another. The presence of a FIB is one attribute that separates a switch from a hub. Without a functional FIB, all frames received by a network switch would be echoed back out to all other ports, much like an Ethernet hub. In bridging packets between ports, a switch should only emit a frame on the port where the destination network device resides (unicast), unless the frame is for all nodes on the switch (broadcast), multiple nodes (multicast) or if the switch doesn't know where the destination device resides (unicast flood).
Switches learn the port on which they first saw a particular source address and associate that port with that address. When the bridge subsequently receives a frame with a destination address in its FIB, it sends the frame out the port stored in the FIB entry.
The FIB is a memory construct used by Ethernet switch to map a station's MAC address to the switch port the station is connected to. This allows switches to facilitate communications between connected stations at high speed.
While the exact mechanics of a forwarding table is implementation-specific, the general model for Frame Relay is that switches have statically defined forwarding tables, one per interface. When a frame with a given data link connection identifier (DLCI) is received on one interface, the table associated with that interface gives the outgoing interface, and the new DLCI to insert into the frame's address field.
ATM switches have link-level forwarding tables much like those used in Frame Relay. Rather than a DLCI, however, interfaces have forwarding tables that specify the outgoing interface by virtual path identifier (VPI) and virtual circuit identifier (VCI). These tables may be configured statically, or they can be distributed by the Private Network-to-Network Interface (PNNI) protocol. When PNNI is in use, the ATM switches at the edges of the network map one of the standard ATM end-to-end identifiers, such as an NSAP address, to the next-hop VPI/VCI.
MPLS has many similarities, at the forwarding level, to ATM. The label edge routers at the edges of an MPLS cloud map between the end-to-end identifier, such as an IP address, and a link-local label. At each MPLS hop, there is a forwarding table that tells the label-switched router which outgoing interface is to receive the MPLS packet, and what label to use when sending the packet out that interface.