Content-Addressable Forwarding or CEF is a method of forwarding packets used in Layer 3 switches and routers. CEF is based on the concept of a forwarding information base (FIB) which stores information on how to forward packets to a particular network.
In layer 3 switches and routers, CEF operations are used to determine how packets should be forwarded. When a packet is received by a Layer 3 switch or router, the device will first look up the destination address in its FIB. The FIB will provide instructions for how the packet should be forwarded. This process is known as CEF switching.
CEF is used on both layer 3 switches and routers, though there are some differences in how it is implemented. On a layer 3 switch, CEF operates at the data link layer, meaning that the switch will look up the destination address in its FIB and forward the packet based on the instructions in the FIB. On a router, CEF operates at the network layer, meaning that the router will look up the destination address and forward the packet based on the instructions in the routing table.
One of the main benefits of using CEF is that it allows for faster packet forwarding. When a packet is received, it is quickly looked up in the FIB or routing table and immediately forwarded to the appropriate destination. This eliminates the need for a CPU to process the packet, which can improve performance and reduce latency.
Another benefit of using CEF is that it allows for better scalability. As the size of a network grows, the FIB or routing table can be easily updated with new entries. This means that the device can continue to forward packets quickly and efficiently with minimal impact to performance.
Despite the benefits of CEF, there are some drawbacks to consider. CEF operations are limited to the data link layer and network layer, meaning that packets cannot be forwarded based on other criteria such as application layer protocols or services. Additionally, CEF operations may not be supported on some switches or routers.
Overall, CEF is a useful method of packet forwarding for Layer 3 switches and routers. CEF operations allow for faster packet forwarding and better scalability, though they are limited to the data link and network layers. When deciding whether to use CEF on a network device, it is important to consider the advantages and drawbacks of CEF.