Basic IP Connectivity and Troubleshooting in Cisco Express Forwarding Troubleshooting IP Connectivity. This chapter covers the following topics Troubleshooting IP connectivity. Troubleshooting punt adjacencies. Clear Computer Memory Vista. Understanding CEF error messages. Troubleshooting commands reference. Cisco Express Forwarding CEF troubleshooting can be tedious, laborious, and difficult. However, most instances of CEF troubleshooting do not require detailed Cisco IOS architecture and platform hardware architecture knowledge. For example, many CEF issues are found in two or three steps of troubleshooting. In addition, many issues that appear to be CEF related end up being a result of a misconfiguration or inoperable end device. The first section of this chapter presents the general troubleshooting used on Cisco IOS routers and switches as a first step in troubleshooting IP connectivity problems. CEF occasionally is the scapegoat for IP connectivity problems, and this chapter helps you verify whether CEF is the root cause of a particular IP connectivity problem. This chapter does not delve into platform specifics of troubleshooting CEF. Remote Computer Access Learn about different remote computer support methods that you can use to have a specialist remotely help you solve a problem on your computer. Fix Most Windows Errors and Problems With Tweaking. Com Windows Repair 4. Major Update Video Using Tweaking. Com Windows Repair to Fix Windows Problems. WiseFixer uses a highperformance detection algorithm that will quickly identify missing and invalid references in your Windows registry. With a few easy steps. A complete listing of all the services installed with Windows 2000 Professional and Server using Service Pack 4 and their functions. The chapter simply approaches troubleshooting from a CEF software switching and command line interface CLI perspective. Most mid to high end routers and all Catalyst switches support distributed CEF d. CEF, or hardware switching. This chapter begins the CEF troubleshooting for all Cisco platforms, including the Cisco 2. Plug And Play Tv Games Namco. Catalyst 6. 50. 0. KB/Media/0000577/00002.png' alt='Disable Ip Helper Windows Xp' title='Disable Ip Helper Windows Xp' />Chapter 5, Understanding Packet Switching on the Cisco Catalyst 6. Supervisor 7. 20, goes into further detail for additional platform and hardware troubleshooting of CEF for the Cisco Catalyst 6. The chapter concludes with a table of the basic CEF troubleshooting commands. As mentioned in the introduction, CEF is a common scapegoat for IP connectivity issues. As such, when approaching an IP connectivity issue, keep an open mind about the root cause of the issue. Although Windows 8, Windows 10 is pretty fast, after using a while, it will start to lag, especially when you have many apps and desktop programs installed. While. This section reviews the methodology for troubleshooting IP connectivity issues, which leads to identifying and troubleshooting CEF issues. The best approach in troubleshooting is to build a troubleshooting plan. Flow charts simplify troubleshooting because they present a stepwise approach to troubleshooting. The following list briefly outlines the first steps in troubleshooting IP connectivity issues and Cisco IOS CEF Step 1 Accurately describe the problem. Step 2 Scope the network topology. Step 3 Review the Open Systems Interconnection OSI model. Verify the physical layer. Verify the Layer 2 layer topology. Step 4 Verify the Address Resolution Protocol ARP table. Step 5 Verify the IP routing table. Step 6 Verify the CEF Forwarding Information Base FIB table. Step 7 Verify the adjacency table. Step 8 Conduct hardware specific troubleshooting. Accurately Describe the Problem. Accurately articulating your IP connectivity problem is paramount to troubleshooting effectively. An ad hoc approach to troubleshooting is usually ineffective in resolving problems. For example, you do not go to your dentist and tell him you are in pain without describing the symptoms, such as which tooth, how often, how intense, how widespread, what causes the pain, and so on. The same premise exists with IP connectivity troubleshooting. To help yourself, you need to know as much about the issue as possible. The following questions aid you in accurately articulating your IP connectivity problem Is your IP connectivity problem isolated to a single end device or multiple end devices Is your IP connectivity problem isolated to a single router or Ethernet switch Does your IP connectivity problem exist only on end devices, or does it affect the management CLI of routers and switches as wellHow widespread is the problem Is the problem widespread or localized to specific area of your network topologyIs the problem intermittent or consistent For example, using the Internet Control Message Protocol ICMP ping utility in Cisco IOS and on end devices, are you getting intermittent responses to ICMP echo requests such as every other response, no responses, or inconsistent responses one out of ten Does this issue depend on packet size If you send ICMP echo requests at different sizes, do you consistently get all your responses or does the problem vary with packet size When did the problem first occurWere there any changes to the network at the same time the problem started occurring These questions aid you in articulating your IP connectivity issues. The next section describes an important next step, building the network topology. Scoping the Network Topology. It is nearly impossible to troubleshoot any type of CEF issue or network connectivity issue without a network diagram that depicts IP addresses, IP routes, devices such as firewalls and switches, and so on. Troubleshooting IP connectivity problems without the aid of a visual topology is nearly impossible unless you can localize the issue to a specific router or switch. In large IP routing scenarios, a network topology is required to troubleshoot connectivity problems. Generally, both logical and physical topologies aid in troubleshooting. Figure 4 1 illustrates a sample physical topology. Reviewing the OSI Model for Troubleshooting. The next step in troubleshooting any IP connectivity issue is to review the OSI model and verify that your issue is indeed a Layer 3 network issue. Figure 4 2 briefly reviews the OSI model. As a reader of this high level technology book on CEF, we assume you have an understanding of the OSI model. The following sections start from the bottom of the OSI model and review troubleshooting physical connectivity and Layer 2 issues that can affect IP connectivity and give the appearance of a CEF issue. Troubleshooting Physical Connectivity. An IP connectivity issue might simply be a Layer 1 physical layer problem. For example, if you are unable to ping a network device through a router, do not assume that you are having a CEF issue. First, ensure that the host is connected and verify that the physical layer between the host and destination is not sustaining errors. Example 4 1 illustrates sample output from a show interfaces command in Cisco IOS. Example 4 1. Verifying the Physical Layer. Switchshow interfaces Gigabit. Ethernet 36. Gigabit. Ethernet. 36 is up, line protocol is up connected. Hardware is Gigabit Ethernet Port, address is 0. MTU 1. 50. 0 bytes, BW 1. Kbit, DLY 1. 0 usec. Encapsulation ARPA, loopback not set. Keepalive set 1. Full duplex, 1. Mbs, link type is auto, media type is 1. Base. SX. input flow control is on, output flow control is off. ARP type ARPA, ARP Timeout 0. Last input 0. 0 0. Last clearing of show interface counters 5w. Input queue 02. Total output drops 0. Queueing strategy fifo. Output queue 04. Received 1. CRC, 0 frame, 0 overrun, 0 ignored. In regard to the show interfaces command and verifying physical connectivity, verify that your ingress and egress interfaces are not sustaining errors such as input errors, cyclic redundancy check CRC errors, output errors, excessive collisions, overruns, late collisions, or output buffer failures. These types of errors can lead to intermittent or total loss of IP connectivity. Generally, physical layer issues cause intermittent connectivity if the connection has link. Layer 1 errors can be a result of a bad cable, bad port, faulty hardware, and so on.