Cisco express forwarding cef is an advanced layer 3 switching technology used mainly in large core networks or the internet to enhance the overall network. Mar 29, 2018 if cisco express forwarding is not running, use the ip cef command to enable central cisco express forwarding or the ip cef distributed command to enable distributed cisco express forwarding. Dec 16, 20 an overview of cisco express forwarding cef cisco express forwarding cef is a packetswitching technique that is the default for many of cisco s router lines over the last ten years. Here is the cisco definition of epoch and how it is used. Packets like these will be expanded to fit the ip length and. Cef optimizes network performance and scalability for networks with large and dy. Cef optimizes network performance and scalability for networks with large and dynamic traffic patterns, such as the internet, on networks characterized by intensive webbased applications, or interactive sessions. Cisco express forwarding book oreilly online learning. Cisco express forwarding cef tables are used to verify that the source addresses and the interfaces on which they were received are consistent with the fib tables on the supervisor engine. Cef stores information in a routecache for optimized lookup and more efficient packet handling. Cisco express forwarding overview afnog 2019 workshop on. Jan 17, 2006 cisco express forwarding cef switching is a proprietary form of scalable switching intended to tackle the problems associated with demand caching.
It uses a fast cache that is maintained in a router data plane. Choose three a mpls b ldp c cisco express forwarding d vss. Cisco express forwarding cef is an advanced layer 3 switching technology used mainly in large core networks or the internet to enhance the overall network performance. When a router routers a packet, the router removes the packets layer 2 header, examine the layer 3 addressing, and decides how to forward the packet. Cef cisco express forwarding if the destination ip address is an address that is configured on the multilayer switch then the ip packet was destined for this. It provides the ability to switch packets through a device in a very quick efficient way while also keeping the load on the routers processor low.
This is the brains of the device which does the decision making. Cisco express forwarding understanding and troubleshooting cef in. Cisco express forwarding cef is advanced layer 3 ip switching technology. Its main purpose is to speed up packer switching and optimize packet forwarding. Finding the cisco express forwarding output information 24 verifying the adjacency or nexthop information 26 verifying distributed cisco express forwarding operation 28 cisco express forwarding command syntax on line cards 28 verifying that dcef switching is enabled 28 locating the prefix in a forwarding table on a line card 29 finding the. Although cef is a cisco proprietary protocol other vendors of multilayer switches or highcapacity routers offer a similar functionality where layer3 switching or routing is done in hardware in an asic instead of by. Which statement about cisco express forwarding is true a the. This book addresses common misconceptions about cef and packet switching across various platforms, helping you to improve your. Cef is a term used to describe one of the mechanisms used by cisco ios routers and cisco catalyst switches to forward packets. Cef is less cpuintensive than fast switching route caching. Cisco express forwarding cef is advanced, layer 3 ip switching technology.
Choose three a mpls b ldp c cisco express forwarding. Router packet forwarding best cisco ccna ccnp and linux. Cisco express forwarding by stringfield, nakia ebook. Ip switching cisco express forwarding configuration guide. Prerequisites requirements there are no specific requirements for this document.
This chapter describes the commands used to configure and monitor cisco express forwarding cef on a cisco asr 9000 series aggregation services router for detailed information about cef concepts, configuration tasks, and examples, see the cisco asr 9000 series aggregation services router ip addresses and services configuration guide. Because there is no need to build cache entries when traffic starts arriving for new destinations, cef behaves more predictably when presented with large volumes of traffic addressed. The time after this instant is in an epoch different from the time before, and the different epochs are numbered between 0 and 255. With cef switching, the information which is conventionally stored in a route cache is split up over several data structures. If cisco express forwarding is not running, use the ip cef command to enable central cisco express forwarding or the ip cef distributed command to enable distributed cisco express forwarding. Cisco express forwarding cef provides the ability to switch packets through a device in a very quick and efficient way while also keeping the. Packet forwarding for all line cards except oc48 and qoc12 packet forwarding for oc48 and qoc12 line cards related information introduction this document explains what cisco express forwarding is, and how it is implemented in the cisco 12000 series internet router. Jan 17, 2006 packet forwarding for all line cards except oc48 and qoc12 packet forwarding for oc48 and qoc12 line cards related information introduction this document explains what cisco express forwarding is, and how it is implemented in the cisco 12000 series internet router. Nexus uses its forwarding mechanism which is similar to cef. Cef stores information in a routecache for optimized lookup and. This video shows you how to more efficiently control your network traffic using cisco express forwarding, or cef.
A new epoch for a cisco express forwarding table begins when a table rebuild is initiated. More cpu processing power can be dedicated to layer 3 services such as quality of service qos and encryption. This document explains what cisco express forwarding is, and how it is implemented in the cisco 12000 series internet router. Ciscos express forwarding cef technology for ip is a scalable, distributed, layer 3 switching solution designed to meet the future performance requirements of. Question 66 which statement about cisco express forwarding is true.
Cisco express forwarding command syntax on line cards 28 verifying that dcef switching is enabled 28 locating the prefix in a forwarding table on a line card 29 finding the distributed cisco express forwarding output information 31 verifying the adjacency or nexthop information on a line card 33. Choose three a mpls b ldp c cisco express forwarding d vss e. With cef cisco express forwarding, we dont have to ask the cpu for first time we trying to route a packet to a specific destination network, because with cef, the cpu is going to proactively populate the fib thats the forwarding information base, thats the layer 3 information. Layer 2 hardware forwarding at 72 mpps layer 3 hardwarebased ip cisco express forwarding routing at 72 mpps layer 4 tcp and user datagram protocol udp hardwarebased filtering at 72 mpps no performance penalty with advanced layer 3 and 4 services enabled softwarebased learning at a sustained rate of 500 hosts per second. The fast cache contains information about how traffic from different data flows should be forwarded. He was a technical contributor and editor of a number of ieee 802 standards, including 802. Jun 22, 2017 cisco express forwarding cef is an advanced layer 3 switching technology used mainly in large core networks to enchance the network performance. What are the two main components of cisco express forwarding.
Cisco express forwarding demystifies the internal workings of cisco routers and switches, making it easier for you to optimize performance and troubleshoot issues that arise in cisco network environments. What are the two main components of cisco express forwarding cef. Forwarding information base the fib is used to make layer3 ip destination prefixbased switching decisions. Ip switching cisco express forwarding configuration guide, cisco. Comparison of network switch architectures by cisco. In this video cheat sheet, were going to be configuring a router for mpls forwarding. Cisco express forwarding paperback networking technology. Ip switching cisco express forwarding configuration guide, cisco ios xe everest 16. Feb 27, 2002 excluding cisco 12000 series internet routers, all cisco devices running cisco ios software that have cisco express forwarding cef enabled can leak information from previous packets that have been handled by the device. This can happen if the packet length described in the ip header is bigger than the physical packet size. It gets its information from the routing table and maintains a mirror. Delivers the industrys highest lan switch performance, 400 mpps, using the distributed cisco express forwarding platform supports a mix of cisco express forwarding implementations and switchfabric speeds for optimal wiring closet, core network, data center, and wan edge deployments, as well as service provider networks.
It is an advanced one in layer 3 switching technology, which is mainly used in the internet or else core networks to enrich the overall performance of the network. When cisco express forwarding or distributed cisco express forwarding is enabled, the show ip cef command shows a brief display of all fib entries. Nxos use not only best routes, but install all routes into the rib from used routing protocols. Learn how to deploy mpls on enterprise and service provider networks. Ultimate guide to cisco express forwardingcef ip with ease. Cisco content hub cisco express forwarding commands. The modern and most preferred cisco ios switching process thats in use on ios equipment is called cisco express forwarding, or cef.
In this lab the network switching equipment currently. This can be done because cef maintains two tables in the data plane. Cisco express forwarding, fast switching, and multicast. With cef, none of the packets are sent to the cpu to be switched. It will cover packet switching techniques like process switching, interrupt context switching fast switching, optimum switching, cisco express forwarding cef. Sep 28, 2017 the cisco express forwarding cef switching mode replaces the traditional cisco routing cache with a data structure that mirrors the entire system routing table. Apr 22, 20 cisco express forwarding demystifies the internal workings of cisco routers and switches, making it easier for you to optimize performance and troubleshoot issues that arise in cisco network environments. The line cards perform the express forwarding between port adapters. Index numerics 31bit prefix network interface, fib entries a active consistency checkers adjacency manager adjacency table auto adjacencies cached. Most of our modern ios devices use cef as the default method.
Cisco express forwarding overview restrictions xc22 cisco ios switching services configuration guide figure 7 cisco express forwarding in a typical highcapacity internet service provider environment, cisco 12012 gsrs as aggregation devices at the core of the network support links to cisco 7500 series routers or other feeder devices. Jun, 2014 cisco express forwarding by nakia stringfield, ccie no. Netflow incorporated separate routing and switching engines. Although cef is a cisco proprietary protocol other vendors of multilayer switches or highcapacity routers offer a similar functionality where layer3 switching or routing is done in hardware in an asic instead of by software and the central cpu. Which statement about cisco express forwarding is true a. Introduction this document is for underlining the different switching or forwarding mechanisms used by routers while making forwarding decision when it receives a packet on an. Express forwarding cef has been introduced for cisco 7200 and 7500 series. This is the decision making part of the forwarding engine where lookups are performed and a decision is made on the frame as to which outgoing. Cisco express forwarding cef must be enabled on all. Cisco express forwarding cef switching is a proprietary form of scalable switching intended to tackle the problems associated with demand caching. The objective of this lab is to monitor the default behavior of cisco express forwarding cef. Cef optimizes network performance and scalability for networks with large and. Netflow was eventually replaced with cisco express forwarding cef, which addressed some of.
After you enable urpf check on an interface pervlan basis, the incoming packet is compared to the cef tables through a reverse lookup. Cisco express forwarding overview cef operation modes xc26 cisco ios switching services configuration guide distributed cef mode when dcef is enabled, line cards, such as vip line cards or gsr line cards, maintain an identical copy of the fib and adjacency tables. Were going to start off with baseline show commands, show ip cef summary to see if. Cisco express forwarding paperback networking technology stringfield, nakia, white, russ, mckee, stacia on. Cisco express forwarding networking technology series by nakia stringfield. Cisco express forwarding concepts and challenges in general network.
Lets see how we can configure cisco express forwarding cef on cisco devices. Cef offers the following advantages to cisco routers. The time after this instant is in an epoch different from the time before, and the. If a interfaces is down and there arent a static route. Cisco express forwarding cef is a packetswitching technique that is the default for most of cisco routing platforms. The forwarding engine is divided into two planes called control plane and data plane. Choose three a mpls b ldp c cisco express forwarding d vss e vpc f vrrp correct from cisco 300175 at kaplan university. The cpu of a router becomes directly involved with packet switching decisions.
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