Ip switching cisco express forwarding configuration guide cef. I noticed that ip cef was not enabled on my 3750 switch stack. Somewhere in the 90s cisco realized that fast switching had its limitations, and a new switching technology was developed which led to. When using process switching the router will remove the header for each. Cef is mainly used to increase packet switching speed by reducing the overhead and delays introduced by other routing techniques. This book addresses common misconceptions about cef and packet switching across various platforms, helping you to improve your.
Cisco content hub cef table consistencycheck through clear pxf. Cisco express forwarding is an advanced layer 3 ip switching technology. Cef cisco express forwarding, l3 switching, rib fib. Packets like these will be expanded to fit the ip length. Posted on april 17, 2017 april 18, 2017 by loopy once again, this is a no nonsense post, with no topology associated to it though there will be some router output to demonstrate things. What is the cisco express forwarding cef feature referred to in cisco documentation and commonly found in cisco ios commands. Cisco express forwarding paperback networking technology. 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. Cisco express forwarding overview cisco express forwarding cef is advanced, layer 3 ip switching technology. Oct 20, 2014 in cisco ios, there are many packet switching methods, but the common ones which we will be discussing in this article are process switching, fast switching and cisco express forwarding cef. 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.
Cef optimizes network performance and scalability for networks with large and. Packets like these will be expanded to fit the ip length and. It operates at layer 3, and is designed to speed up packet switching, cef supports ethernet, frame relay, ppp, atm, fddi, tunnels and hdlc. 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. The vulnerability allows an attacker to access arbitrary information from previous packets to be disclosed. Apr 22, 2018 the same applies with taking for granted the way things work, be that arp, dhcp or the process a switch or router goes through when moving traffic. Cisco ios with cisco express forwarding information.
According to ciscos website, cisco express forwarding cef is advanced, layer 3 ip switching technology. He was a technical contributor and editor of a number of ieee 802 standards, including 802. This is the fastest method but there are some limitations. So cisco came up with the idea to cache information to the interface processors. Cef keeps two tables, the fib forwarding information base, and the adjacency table, which. If cisco express forwarding for ipv6 or distributed cisco express forwarding for ipv6 is enabled globally on the router, the show cef not cef switched command displays ipv6 cisco express forwarding counter information and ipv4 cisco express forwarding counter information. Cisco express forwarding cef issue preamble a couple years ago i managed to get hold of some ancient cisco equipment, probably a pile of rubble to the eyes of professionals, but a little treasure for a young man like me that wanted to learn something about networking. Cef is used on cisco devices to ensure packets can be forwarded without any noticable delays. Cisco content hub show adjacency through show ip cef with.
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. From a 500 foot view cef is a method the router uses to forward packets, without utilizing any cpu cycles. Cef cisco express forwarding also known as topology based switching. Its an improvement over fast switching and route processor switching. 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. With cef switching, the information which is conventionally stored in a. Cisco express forwarding cef provides the ability to switch packets through a device in a very quick and efficient way while also keeping the load on the routers processor low. Ef expedited forwarding not express forwarding hence the confussion with cef. Feb 19, 2018 understanding cisco express forwarding.
In most scenarios the phone would mark the voice stream as e, the switch would honor this. Oct 11, 2012 cef known as cisco express forwarding is a feature built into every cisco router and is enabled by default its really the feature that makes cisco well cisco. However, most instances of cef troubleshooting do not require. What is the difference between routing a packet, switching a frame, and packet switching. Cef seems to be such a big part of cisco networking, just curious if there are alternatives that are also topology based nonroute caching.
Cisco express forwarding book oreilly online learning. Cisco express forwarding cef is advanced layer 3 ip switching technology. If cef is disabled and fast switching is enabled, the router begins to populate its fast cache. If a change occurs on the routing table, it is also reflected in the fib. Jan 17, 2006 cisco express forwarding cef switching is a proprietary form of scalable switching intended to tackle the problems associated with demand caching. Ip switching cisco express forwarding configuration guide iii. Cef abbreviation stands for cisco express forwarding.
This feature module details changes to commands that are required to support updates to cisco express forwarding. Cisco express forwarding cef switching is a proprietary form of scalable switching intended to tackle the problems associated with demand caching. Ciscos implementation of this architecture is know as cisco express forwarding cef process switching the routermls processes every packet to make a forwarding decision. Cisco express forwarding cef is a packetswitching technique that is the default for many of ciscos router lines over the last ten years. 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. Cisco express forwarding cef troubleshooting can be tedious, laborious, and difficult.
Alternatives to cef cisco express forwarding in terms of multilayer switching, what do other hardware manufactures use. Cisco express forwarding cef ip with ease ip with ease. It provides the ability to switch packets through a. Due to this the router is able to perform routing at much lower latency and higher throughput while maintaining low cpu utilization. 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. If cisco express forwarding is enabled, you receive output that looks like this. Cef, or cisco express forwarding, is a layer 3 switching technology. Central cef mode operation you can use central cisco express forwarding mode when line cards are not available for cisco express forwarding switching, when you need to use features not compatible with distributed cisco express forwarding switching, or when you are running on a platform that is not a distributed platform. Cef known as cisco express forwarding is a feature built into every cisco router and is enabled by default its really the feature that makes cisco well cisco. Cef cheats a little, by building a forwarding information base fib, and an adjacency table.
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. So i would check the phones are configured correctly, then on the hp switch i would use the following commands. 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. The cisco express forwarding cef switching mode replaces the traditional cisco routing cache with a data structure that mirrors the entire system routing table. 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. Resolution cisco express forwarding cef is advanced, layer 3 ip switching technology. Cisco arp resolution, cam table population, fib table lookup duration.
Cisco express forwarding cef, is the evolution of optimizing the router to make it be able to forward more packets faster. Ip switching cisco express forwarding configuration. Cisco express forwarding cef is an advanced layer 3 switching technology used mainly in large core networks to enchance the network performance. Cisco express forwarding cef is a packetswitching technique that is the default for many of ciscos router. Cisco express forwarding cef is a packetswitching technique that is the default for many of cisco s router lines over the last ten years. Cisco express forwarding paperback networking technology stringfield, nakia, white, russ, mckee, stacia on. Cef cisco express forwarding my internets not working. 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 forwarding of ip packets is done by the forwarding plane, also called the data plane.
This can happen if the packet length described in the ip header is bigger than the physical packet size. Cef optimizes network performance and scalability for. Router packet forwarding best cisco ccna ccnp and linux. Dec 16, 20 an overview of cisco express forwarding cef 1. Cisco express forwarding or cef for short is a layer 3 switching technology propriety to cisco. Cisco catalyst 3850 configuration manual pdf download. Apr 19, 2014 cisco express forwarding cef is advanced, layer 3 ip switching technology. How to troubleshoot ip connectivity and cisco ios cef. How to troubleshoot ip connectivity and cisco ios cef troubleshooting problems with cisco express forwardings network switching is easier than you might think. Cef allows hardware level routing switching to happen without using cpu cycles. I was going to enable it, but it is asking me for the type of cef. In this article, we will be focusing on ip packets although the same concept applies to other protocol packets. It is an advanced one in layer 3 switching technology, which is mainly used in the internet or else core networks.
Cisco express forwarding cef is a packetswitching technique used within cisco routers. Ip switching cisco express forwarding configuration guide. I figured i would take a little time and discuss cef in a little detail. Cisco express forwarding by nakia stringfield, ccie no.
An overview of cisco express forwarding cef cisco express forwarding cef is a packetswitching technique that is the default for many of ciscos router lines over the last ten years. This document explains what cisco express forwarding is, and how it is implemented in the cisco 12000 series internet router. Cisco parallel express forwarding pxf is used to accelerate forwarding performance on the cisco 7304 router. Jun, 2014 cisco express forwarding by nakia stringfield, ccie no. One thought on cisco express forwarding cef load balancing ali i. I came across some of my old notes on cef which i thought i would share. Cef cisco express forwarding an optimized layer 3 forwarding path through a router or a multilayer switch. Feb 27, 20 cisco express forwarding cef is a packetswitching technique that is the default for many of ciscos router lines over the last ten years. In this chapter from cisco express forwarding, learn how to identify and fix common problems, many of which dont require extensive knowledge of ciscos architecture and platforms.
Cisco express forwarding and the forwarding information. The fib, or forwarding information base, is a direct copy of the routing table. Cisco express forwarding cef must be enabled on all. Comprension del cisco express forwarding cef cisco. Cef cisco express forwarding, l3 switching, rib fib explained, and a ton of good info important for exam day. Somewhere in the 90s cisco realized that fast switching had its limitations, and a new switching technology was developed which led to cef cisco express forwarding. Cisco express forwarding understanding and troubleshooting cef in cisco routers and switches how does a router switch a packet. The following example enables the cisco express forwarding consistency checker to check ipv4 addresses and specifies the scanrplc checker to run every 60 seconds for 5000 prefixes. Lets see how we can configure cisco express forwarding cef on cisco devices. Cisco express forwarding cef issue cisco community. Cisco express forwarding on a 3750 solutions experts exchange.
What is the abbreviation for cisco express forwarding. Ip switching cisco express forwarding configuration guide, cisco. Cef keeps two tables, the fib forwarding information base, and the adjacency table, which contains the layer 2 information for. Prior to cef there were 2 methods for packetswitching process switching and fastswitching. Cisco express forwarding cef is advanced, layer 3 ip switching technology. Cisco express forwarding afnog 2019 workshop on network. The list of acronyms and abbreviations related to cef cisco. 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. I wonder if cef loadsharing universal andor layer 4 source port algorithm is similar to the loadsharing algorithm used by etherchannels.
If cisco express forwarding for ipv6 or distributed cisco express. With cef switching, the information which is conventionally stored in a route cache is split up over several data structures. Cisco express forwarding cef is a packetswitching technique that is the default for most of cisco routing platforms. When cisco express forwarding or distributed cisco express forwarding is enabled, the show ip cef command shows a brief display of all fib entries. Cisco express forwarding concepts and challenges in general network. 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 sessi. Cisco express forwarding cef maintains its information in two tables, the adjacency table which contains information about layer 2 adjacencies and the forwarding information base fib which contains layer 3 information.
Cef optimizes routing table lookup by creating a special, easily searched structure based on the contents of the ip routing table, and preconstructs frame headers for directly connected end hosts and next hops. A vulnerability exists in cisco routers running cisco ios with cisco express forwarding cef enabled. In my last post about unicast reverse path forwarding, i made quite a few references to cef. The main purpose of cef is to optimize the forwarding of packets and increase the packet switching speed. Cisco has developed a more efficient form of multilayer switching called cisco express forwarding cef. Cisco content hub cef table consistencycheck through. Cef provides the ability to switch packets through advanced, layer 3 ip switching technology via a device in a way that minimises load on routers processor. Fast switching the initial packets forwarding decision is still derived from the route processor, but that destination is then held in cache for subsequent. Cefdcef cisco express forwarding cisco ios xe release 2. 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. Identify cisco express forwarding concepts ccie wiki. Cef optimizes network performance and scalability for networks with large and dynamic traffic patterns, such as the.
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