By Stringfield N., White R., McKee S.
Cisco show Forwarding figuring out and troubleshooting CEF in Cisco routers and switches Nakia Stringfield, CCIER No. 13451Russ White, CCIE No. 2635Stacia McKee How does a router swap a packet? what's the distinction among routing a packet, switching a body, and packet switching? what's the CiscoR exhibit Forwarding (CEF) characteristic mentioned in Cisco documentation and in most cases present in Cisco IOSR instructions? CEF is a common time period that describes the mechanism in which Cisco routers and CatalystR switches packet-switch (route) frames. CEF is located in just about all Cisco routers and Catalyst switches, and knowing how CEF operates can enhance the functionality, scalability, and potency of your community. Cisco convey Forwarding demystifies the interior workings of Cisco routers and switches, making it more uncomplicated so you might optimize functionality and troubleshoot concerns that come up in Cisco community environments. This e-book addresses universal misconceptions approximately CEF and packet switching throughout a variety of structures, assisting you to enhance your troubleshooting talents for CEF- and non-CEF-related difficulties. the 1st a part of the ebook offers an outline of packet-switching architectures and CEF operation and complicated features.It additionally covers the improved CEF constitution and basic troubleshooting. the second one a part of the e-book offers case reports that target the typical issues which have been complicated for patrons and people aiding Cisco networks. packed with sensible examples and configurations, this e-book attracts on years of expertise that will help you hold your Cisco networks operating successfully. Nakia Stringfield, CCIER No. 13451, is a community consulting engineer for complex companies at Cisco, helping most sensible monetary clients with community layout and utilising most sensible practices. She used to be previously a senior customer service engineer for the Routing Protocols Technical advice heart (TAC) staff troubleshooting matters regarding CEF and routing protocols. Nakia has been with Cisco for greater than six years, formerly serving as a technical chief for the structure TAC staff. Russ White, CCIE No. 2635, is a precept Engineer within the Routing Protocol layout and structure group at Cisco. he's a member of the IETF Routing quarter Directorate, co-chair of the Routing Protocols safety operating workforce within the IETF, a standard speaker at Cisco Networkers, a member of the CCIE content material Advisory team, and the coauthor of six different books approximately routing and routing protocols, together with optimum Routing layout from Cisco Press. Russ basically works within the improvement of latest good points and layout architectures for routing protocols. Stacia McKee is a customer service engineer and technical chief of the Routing Protocols Technical guidance heart (TAC) crew. This workforce specializes in delivering post-sales aid of IP routing protocols, MPLS, QoS, IP multicast, and plenty of different Layer three applied sciences. Stacia has been with Cisco for greater than six years, formerly serving as a technical chief of the structure TAC group and a member of the WAN/Access TAC workforce. research the major good points of packet-switching architecturesUnderstand the fundamentals of the CEF structure and operationExamine the improved CEF constitution, which improves scalabilityLearn tips to troubleshoot in software-switching environmentsUnderstand the impression of CEF on a Cisco Catalyst 6500 manager 720Configure and troubleshoot load sharing with CEFEvaluate the impact of CEF in an MPLS VPN environmentReview CEF layout issues that impression scalability
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Extra info for Cisco Express Forwarding
The following list briefly outlines the order of operation of a packet as it is being process-switched through a router: 1. The router reads the packet off the wire connected to the inbound interface. 2. The router stores the packet in memory. 3. The router performs a lookup in the global routing table for the packet's destination IP address. 4. The router finds the next-hop IP address toward the destination by resolving any recursion within the routing table. 5. The router finds the physical Layer 2 header and outbound interface for the next-hop device.
2. Router B sends an ARP request for this host destination. 8, responds to the ARP request with its MAC address embedded. 3. Router B receives the ARP reply and builds a new ARP entry. 4. 8/32, on Router B. 8. Figure 2-10. Glean Adjacency [View full size image] Drop Adjacency The FIB points to a drop adjacency when packets switched to this destination should be dropped upon being received. Drop adjacencies obey any configured Internet Control Message Protocol (ICMP) requirements. 0/4 on a router that does not have IP Multicast Routing enabled.
If a parent's path information changes, any dependents will also be reresolved. CEF does not limit the amount of levels required for recursion. 2S, which is covered in Chapter 3. On a router running pre-MFI IOS, multilevel recursion with load balancing results in CEF using all the paths at the first level and then choosing only one of the paths at the subsequent levels. The results do not guarantee that load balancing will occur because of lack of code support. Default Route Handler FIB Entry The FIB installs the default route handler entry as a default entry placeholder.