Category Archives: Routing

Understanding CEF?

Cisco Express Forwarding (CEF) is advanced, Layer 3 IP switching technology. CEF optimizes network performance and scalability for networks with large and dynamic traffic patterns, such as the Internet, on networks characterized by intensive Web-based applications, or interactive sessions.

Layer 3 switch process

a. Process switching
– Requires the CPU to be personally involved with every forwarding decision.
– Whenever any packet enters the router, Router will do a layer 3 lookup(software based) change the destination Ip and check the next-hop then finds the exit interface.

b. Fast switching
– Still uses the CPU, but after a packet has been forwarded information about how to reach the destination is stored in a fast-switching cache.
– Same process with process switching, lookup then locate the destination IP and check the nexthop and exit interface..but we save the the detail on cache.

This two method no longer used by our routers.

c. Cisco Express Forwarding (CEF)
– Optimizing the router to it be able to forward mode packets faster.
– Before packet arrive to the router,

FYI

RIB – IP Protocols populate the RIB
– A control plane
– show ip route

CEF – RIB populates CEF and its FIB
– Data Plane
– show ip cef

LIB – LDP polupulates the LIB
– Control plance
– show mpls ldp binding

LFIB – LDP and RIB populates the LFIB
– Data plane
– show mpls forwarding-table

How to Verify Cisco Express Forwarding Switching
https://www.cisco.com/c/en/us/support/docs/ios-nx-os-software/ios-software-releases-120-mainline/47205-cef-whichpath.html