By Stringfield N., White R., McKee S.
Cisco exhibit 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 change a packet? what's the distinction among routing a packet, switching a body, and packet switching? what's the CiscoR convey Forwarding (CEF) function observed in Cisco documentation and in most cases present in Cisco IOSR instructions? CEF is a common time period that describes the mechanism through 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 increase the functionality, scalability, and potency of your community. Cisco convey Forwarding demystifies the inner workings of Cisco routers and switches, making it more straightforward so you might optimize functionality and troubleshoot matters that come up in Cisco community environments. This e-book addresses universal misconceptions approximately CEF and packet switching throughout a variety of structures, supporting you to enhance your troubleshooting abilities for CEF- and non-CEF-related difficulties. the 1st a part of the publication offers an summary of packet-switching architectures and CEF operation and complicated features.It additionally covers the improved CEF constitution and normal troubleshooting. the second one a part of the e-book presents case experiences that concentrate on the typical themes which were difficult for patrons and people aiding Cisco networks. filled with sensible examples and configurations, this publication attracts on years of expertise that will help you maintain your Cisco networks working successfully. Nakia Stringfield, CCIER No. 13451, is a community consulting engineer for complicated providers at Cisco, assisting best monetary consumers with community layout and using most sensible practices. She used to be previously a senior customer service engineer for the Routing Protocols Technical advice middle (TAC) staff troubleshooting concerns concerning 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 crew at Cisco. he's a member of the IETF Routing region Directorate, co-chair of the Routing Protocols safeguard operating staff within the IETF, a typical 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 essentially works within the improvement of latest gains and layout architectures for routing protocols. Stacia McKee is a customer service engineer and technical chief of the Routing Protocols Technical guidance middle (TAC) group. This group makes a speciality of supplying post-sales help of IP routing protocols, MPLS, QoS, IP multicast, and lots 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 crew and a member of the WAN/Access TAC staff. study the main beneficial properties of packet-switching architecturesUnderstand the fundamentals of the CEF structure and operationExamine the improved CEF constitution, which improves scalabilityLearn how one can troubleshoot in software-switching environmentsUnderstand the influence of CEF on a Cisco Catalyst 6500 manager 720Configure and troubleshoot load sharing with CEFEvaluate the impression of CEF in an MPLS VPN environmentReview CEF layout issues that effect scalability
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Extra resources for Cisco Express Forwarding
This node points to the 16th node, which in turn, points to the first node. 1. 100/32. Figure 2-4. Structure of the FIB If the final node exists, you know that the network in question is reachable. The behavior in this example is called a longest-match lookup, which the router performs on the destination IP address of packets being forwarded through the router. The output of the command show ip cef [[network][mask]] displays longest-match lookups for entries in the FIB. On the contrary, exact-match lookups are performed by the router for packets destined to the router's control plane.
To confirm that CEF or dCEF has been configured and is enabled, enter the show ip cef command, as shown in Example 2-23. Example 2-23. 255/32 Next Hop drop receive attached receive receive receive attached receive receive receive drop receive receive Interface Null0 (default route handler Serial2/0 Ethernet0/0 Chapter 3. CEF Enhanced Scalability This chapter covers the following topics: • Fundamental changes to CEF for CCSR • Changes to show commands • New show ip cef commands • New show cef commands • CEF event logger • CEF consistency checker • New CEF processes Cisco Express Forwarding (CEF) is the most widely used forwarding mechanism on IP networks, so why change what works?
This is the transmit interrupt. The code that runs during the transmit interrupt updates the interface counters. 4. During the transmit interrupt, the packet buffer is returned to the pool from which it was drawn when the packet was created (if it was locally generated) or the pool from which the packet buffer was drawn when it was placed on the inbound interface's receive ring. This completes the entire cycle, returning the resources to their original location. After the packet buffer has been returned to the pool from which it was drawn and the interface counters have been updated, the transmit interrupt is released, and the processor continues running the process that was interrupted.