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FE (Forwarding element)

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A forwarding element (FE) is a component in a computer network that is responsible for forwarding data packets between different network nodes. The FE can be implemented in hardware, software or a combination of both, and is typically found in network devices such as routers, switches, and gateways.

The role of the forwarding element is to receive incoming packets on one interface and then forward them out of another interface towards their destination. The destination can be another device on the same network, or it can be a device on a different network. The FE performs this forwarding process by examining the destination address in the packet header and looking up a forwarding table to determine the appropriate outgoing interface for the packet.

There are several important components of a forwarding element, which include:

  1. Input port: This is the interface on which the FE receives incoming packets. The input port is responsible for buffering and queuing incoming packets until they can be processed by the forwarding engine.
  2. Forwarding engine: This is the component that performs the actual forwarding of packets. The forwarding engine examines the destination address in the packet header and looks up the appropriate outgoing interface in the forwarding table.
  3. Output port: This is the interface on which the FE forwards outgoing packets. The output port is responsible for queuing and buffering packets until they can be transmitted on the network.
  4. Forwarding table: This is the data structure that is used by the forwarding engine to determine the appropriate outgoing interface for each incoming packet. The forwarding table contains entries that map destination addresses to outgoing interfaces.
  5. Control plane: This is the component that is responsible for configuring and maintaining the forwarding table. The control plane communicates with other network devices to exchange routing information and update the forwarding table accordingly.

There are several types of forwarding elements, including:

  1. Store-and-forward switching: In this type of switching, the forwarding element receives an entire packet before forwarding it. This allows the forwarding element to perform error checking and verify the integrity of the packet before forwarding it.
  2. Cut-through switching: In this type of switching, the forwarding element begins forwarding the packet as soon as the destination address is received. This reduces latency, but it also means that errors may be forwarded along with the packet.
  3. Fragment-free switching: This type of switching combines the benefits of store-and-forward and cut-through switching. The forwarding element examines the first 64 bytes of the packet to check for errors, but then forwards the rest of the packet without buffering.

Forwarding elements can also be classified based on the network layer they operate at. For example:

  1. Layer 2 forwarding elements: These operate at the data link layer and are responsible for forwarding packets based on MAC addresses.
  2. Layer 3 forwarding elements: These operate at the network layer and are responsible for forwarding packets based on IP addresses.
  3. Layer 4 forwarding elements: These operate at the transport layer and are responsible for forwarding packets based on port numbers.

Forwarding elements play a critical role in modern computer networks. They are responsible for ensuring that packets are delivered to their intended destinations in a timely and reliable manner. As such, they must be highly reliable and efficient. Forwarding elements are often designed to operate at high speeds and must be able to handle large volumes of traffic without dropping packets or introducing latency.

In addition to forwarding packets, forwarding elements may also perform other functions such as filtering, packet inspection, and quality of service (QoS) control. For example, a forwarding element may be configured to prioritize certain types of traffic or to block packets that are suspected to be malicious.

In conclusion, forwarding elements are an essential component of modern computer networks. They are responsible for ensuring that packets are delivered to their intended destinations in a timely and reliable manner. Forwarding elements operate at various network layers and can be implemented in hardware, software, or a combination of both. They consist of several important components, including input ports, forwarding engines, output ports, forwarding tables, and control planes. Forwarding elements can also be classified based on the type of switching they perform and the network layer they operate at.

The design of forwarding elements is an important consideration when designing computer networks. Factors such as performance, scalability, and reliability must be carefully considered to ensure that the network can handle the required traffic volumes without introducing latency or dropping packets. The choice of forwarding element will depend on the specific requirements of the network and the applications it supports.