Module 9.0 ? Troubleshooting 9.0 ? Introduction 9.0.1 - Introduction One Diagram Diagram 1, Animation Slide 1 Troubleshooting configuration or operation problems requires the application of networking knowledge and skills. Slide 2 Employers value networkers who can troubleshoot in an organized manner to identify symptoms, isolate the causes, and fix the problems quickly. Slide 3 Cisco Career Certifications bring valuable, measurable rewards to network professionals and the organizations that employ them. Slide 4 Troubleshooting can help prepare you to successfully obtain a Cisco Certified Entry Networking Technician (CCENT) certification. Slide5 After completion of this chapter, you should be able to: * Use the OSI model as a framework for troubleshooting network problems. * Identify and correct problems with hardware and operation at Layer 1 and Layer 2. * Troubleshoot IP addressing problems, including subnet mask, host range errors, DHCP and NAT issues. * Identify and correct problems with RIPv2 configuration and implementation. * Explain possible causes of problems occurring with user applications and how to recognize symptoms of DNS failures. * Create a plan to prepare to take the ICND1 examination in order to obtain a CCENT certification. 9.1 - Troubleshooting Methodologies and Tools 9.1.1 - The OSI Model and Troubleshooting Four Diagrams Diagram 1, Image OSI Model Application Layer * Defines interfaces between application software and network communication functions. * Provides standardized services such as file transfer between systems. Presentation Layer * Standardizes user data formats for use between different types of systems. * Encodes and decodes user data; encrypts and decrypts data; compresses and decompresses data. Session Layer * Manages user sessions and dialogues. * Manages links between applications. Transport Layer * Manages end-to-end message delivery over the network. * Can provide reliable and sequential packet delivery through error recovery and flow control mechanisms. Network Layer * Provides logical network addressing. * Routes packets between networks based on logical addressing. Data Link Layer * Defines procedures for operating the communication links. * Detects and corrects frame transmit errors. * Adds physical addresses to frame. Physical Layer * Defines physical means of sending data over network devices. * Interfaces between network medium and devices. * Defines optical, electrical, and mechanical characteristics for both wired and wireless media. * Includes all forms of electromagnetic transmission such as light, electricity, infrared, and radio waves. TCP/IP Model Application This layer has the same functionality as the Application, Presentation and Session layers of the OSI model. Transport This layer has the same functionality as the Transport layer of the OSI model. Internet This layer has the same functionality as the Network layer of the OSI model. Network Access This layer has the same functionality as the Data link and Physical layers of the OSI model. Diagram 2, The following devices function on the indicated layers of the OSI model. Router 4 Transport 3 Network 2 Data Link 1 Physical Firewall 4 Transport 3 Network 2 Data Link 1 Physical Standard Switch 2 Data Link 1 Physical Hub 1 Physical End System 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical Diagram 3, Activity Identify the layer to which the protocol or technology belongs. Protocol or Technology Radio waves Hubs Repeaters Twisted Pair Cable Electrical signaling Ethernet LAN Switching MAC addresses Network Interface Cards Frames Routing IP addresses Packets Port Numbers TCP UDP Telnet Client Software SMTP FTP HTTP Selectable Layer Physical Layer Data Link Layer Network Layer Transport Layer Upper Layers Diagram 4, Hands-on Lab. 9.1.2 - Troubleshooting Methodologies Two Diagrams Diagram 1, Image Application, Presentation, Session Troubleshooting Approach: Top-down How it operates: Always starts at the application layer and works its way down until it finds a faulty layer. Cases for which it is suitable: More suitable for simpler problems or those that are suspected to be application/user or upper-layer related. Advantages/ Disadvantages: If the problem turns out to be related to lower layers, you have wasted a lot of time and effort at the upper or application layers. Transport Troubleshooting Approach: Divide-and-conquer How it operates: Based on the circumstances (reported issues) and your experience, you might decide to start at any layer and work up or down the OSI stack. Cases for which it is suitable: Most suitable when you are experienced and the problem has precise symptoms. Advantages/ Disadvantages: It targets the problem layer faster than the other approaches. You need experience to use this approach effectively. Network Troubleshooting Approach: Divide-and-conquer How it operates: Based on the circumstances (reported issues) and your experience, you might decide to start at any layer and work up or down the OSI stack. Cases for which it is suitable: Most suitable when you are experienced and the problem has precise symptoms. Advantages/ Disadvantages: It targets the problem layer faster than the other approaches. You need experience to use this approach effectively. Data Link Troubleshooting Approach: Divide-and-conquer How it operates: Based on the circumstances (reported issues) and your experience, you might decide to start at any layer and work up or down the OSI stack. Cases for which it is suitable: Most suitable when you are experienced and the problem has precise symptoms. Advantages/ Disadvantages: It targets the problem layer faster than the other approaches. You need experience to use this approach effectively. Physical Troubleshooting Approach: Bottom-up How it operates: Always starts at the physical layer and works its way up until it finds a faulty layer. Cases for which it is suitable: More suited for complex cases. Advantages/ Disadvantages: It is a slow, but solid approach. When the problem is application-related (or upper layer-related), this approach can take a long time. Diagram 2, Activity Customers report that they are unable to view web pages from a web server located at the ISP. Place the actions taken by the technician into the correct troubleshooting method category. Technicians Actions A. The technician suspects that a firewall is causing the problem, and checks the firewall configuration. B. The technician checks the cable connections between the web server and the directly connected switch. C. The technician pings the server and then pings the switch located at the customer site. D. The technician calls the customer in order to determine if only web applications are affected. E. The technician checks the lights on the network interface card in the web server. F. The technician verifies that the server has the correct DNS entry and that it is resolving the name. G. You have placed the actions taken by the technician into the correct troubleshooting method category. Click Next to continue. Troubleshooting Method 1. Bottom-up Troubleshooting 2. Top-down Troubleshooting 3. Divide-and-conquer Troubleshooting 9.1.3 - Troubleshooting Tools Four Diagrams Diagram 1, Image Physical Topology The actual physical wired topology of the network e.g., how the routers are connected to the servers, the switches and the hosts within that network. Logical Topology How the network is set up in terms of addressing e.g., the diagram shows subnets, broadcast domains and other addressing related issues. Diagram 2, Image Baseline Tools Screen shots of the following tools: * SolarWinds LANsurveyor (Automated Network Mapping Tool) * SolarWinds CyberGauge (Bandwidth Monitoring Tool) NMS Screen shots of the following tools: * WhatsUp Gold NMS Device Status Display Knowledge Base Screen shots of resource tools and resources ? Cisco Systems website Protocol Analyzer Screen shots of the following tools: * Wireshark Protocol Analyzer Diagram 3, Hands-on Lab Diagram 4, Image Multimeter Image of Fluke 179 Digital Multimeter. Cable Tester Two images one of Fluke Networks LinkRunner Pro Tester and Fluke Networks CableIQ Qualification Tester. Network Analyzer Image of Fluke Networks OptiView Series III Integrated Network Analyzer 9.1.4.0 - Certification Study Guide Single Diagram Diagram 1, Hands-on Lab CCENT Study Guide Please see your instructor for further information. 9.2 - Troubleshooting Layer 1 and Layer 2 Issues 9.2.1 - Layer 1 and 2 Problems Three Diagrams Diagram 1, Image 1 Physical Layer Performance lower than baseline * Inadequate cable or poor terminations can result in errors that increase the rate of retransmissions. * Electrical interference may cause poor performance over copper links. * Cabling that exceeds the recommended standard distance limitations can cause attenuation problems. * In a wireless network, interference or a significant increase in traffic can cause network responses to degrade. Loss of connectivity * Intermittent loss can be caused by power-related problems, such as a failing UPS or power supply, resulting in a device reboot or temporary link or device failure. Loose connections and tension on the connectors and wires can also cause intermittent loss. * For wireless coverage areas, intermittent connectivity can be caused by overlapping wireless channels. * Complete loss can be caused by a cable connection failure or a failed device or interface. High collision counts * Average collision counts on shared media should generally be below 1% of total traffic. * Collision-based problems are often traced to a single source, such as a bad uplink cable on a hub or switch port, or a link that is exposed to external electrical noise. * Too many hosts on a single shared segment can contribute to high collision rates. * Duplex mismatches between devices can cause collisions to be recorded on a switch link. * A full-duplex switch port should have no collisions. Network bottlenecks or congestion * When congestion occurs, frames can be dropped. * Unexpected high rates of traffic on devices or cables not designed to handle the load can cause congestion. * Malware, such as Trojans and worms can cause Layer 1 devices and cabling to become congested. * A protocol analyzer can assist in finding the source of high traffic related problems. High CPU utilization rates * High CPU utilization indicates that a device is operating at or exceeding its design limits. * CPU overloading can cause a device to shut down or fail. Console error messages * Error messages reported on the device console can indicate a Physical Layer problem. * Messages indicating that a device or protocol is down indicate interface or cabling problems. Diagram 2, Image 2 Data Link Layer No functionality or connectivity at the Network Layer or above * Misconfigured network cards or faulty NIC drivers can stop the exchange of frames across a link. * Encapsulation errors on serial or WAN links can also cause connectivity to fail over operational circuits. Network operating below baseline performance levels * Interfaces dropping frames that exceed the capacity of the interface or have CRC or framing errors can cause poor network performance. These problems can be identified through error counter statistics and console error messages on the switch or router. * Faulty NICs, interface errors, and electric noise are common Layer 1 hardware issues that can create Layer 2 framing errors in the network. Excessive broadcasts * Large Layer 2 network segments can contribute to excessive broadcasts. * Viruses and worms can add excessive broadcast traffic to the network. Console error messages * Console messages typically occur when the device detects a problem with interpreting incoming frames because of encapsulation or framing problems. * Messages also occur when keepalives are expected but do not arrive. * The most common console message that indicates a Layer 2 problem is a line protocol down message. Diagram 3, Activity Activity Match the Layer 1 or Layer 2 problem with possible symptom. Symptoms A. Failing UPS or power supply. B. Loose cable. C. Too many hosts on a shared network segment. D. Duplex mismatch. E. No keepalive signals are being received. F. Encapsulation mismatch. Layer 1 or Layer 2 problems 1. Intermittent loss of connectivity. 2. Excessive collisions on an interface. 3. Console message indicating a protocol is down. 9.2.2 - Troubleshooting Device Hardware and Boot Errors Three Diagrams Diagram 1, Image Stage 1 ROM POST Perform Post Perform POST ROM Bootstrap Load Bootstrap Execute Bootstrap Loader System Bootstrap, Version 12.3(8r)T8, RELEASE SOFTWARE (fc1) Cisco 1841 (revision 5.0) with 114688K/16384K bytes of memory. Stage 2 Flash Cisco Internetwork Operating System Locate and load Operating system Locate the IOS TFTP Server Cisco Internetwork Operating System Locate and load Operating system Load the IOS System Bootstrap, Version 12.3(8r)T8, RELEASE SOFTWARE (fc1) Cisco 1841 (revision 5.0) with 114688K/16384K bytes of memory. Self decompressing the image: ######################################################[OK] Stage 3 NVRAM Configuration Locate and load Configuration file or enter "setup" mode Locate the Configuration file TFTP Server Configuration Locate and load Configuration file or enter "setup" mode Execute the Configuration file... Console Configuration Locate and load Configuration file or enter "setup" mode Enter Setup Mode System Bootstrap, Version 12.3(8r)T8, RELEASE SOFTWARE (fc1) Cisco 1841 (revision 5.0) with 114688K/16384K bytes of memory. Self decompressing the image: ######################################################[OK] Restricted Rights Legend Use, duplication, or disclosure by the Government is subject to restrictions as set fourth in subparagraph (c) of the Commercial Computer Software ? Restricted Rights clause at Far sec. 52.227.19 and subparagraph (c) (1) (ii) of the Rights in Technical Data and Computer Software clause at DFARS sec. 252.227-7013. Cisco Systems, Inc. 170 West Tasman Drive San Jose, California 95134-1706 Cisco IOS Software, 1840 Software (C1841-IPBASE-M), Version 12.3(14)T7, RELEASE SOFTWARE (fc2) Technical Support: http//www.cisco.com/techsupport Copyright (c) 1986-2006 by Cisco Systems, Inc. Compiled Mon 15-May-06 14:54 by pt_team Image text-base: 0x6007D180, data-base: 0x61400000 Port Statistics for unclassified packets is not turned on. Cisco 1841 (revision 5.0) with 114688K/16384K bytes of memory. Processor board ID FTX0947Z18E M860 processor: part number 0, mask 49 2 FastEthernet/IEEE 802.3 interface(s) 2 Low-speed serial (sync/async) network interface(s) 191K bytes of NVRAM/ 3130K bytes of ATA CompactFlash (Read/Write) Cisco IOS Software, 1841 Software (C1841-IPBASE-M), Version 12.3(14)T7, RELEASE SOFTWARE (fc2) Technical Support: http://www.cisco.com/techsupport Copyright (c)1986-2006 by Cisco Systems, Inc. Compiled Mon 15-May-06 14:54 by pt_team Diagram 2, Tabular 1841 LED Indicators on successful boot LED: SYS PWR Color: Green Status: Router has successfully booted up and the software is functional. Slow, steady blinking when system is booting or in the ROM monitor. LED: STS ACT Color: Green Status: Blinking when packets are transmitted or received on an WAN or LAN interface, or when monitoring system activity. LED: CF Color: Blinking Green Status: Flash memory is busy. Do not remove the CompactFlash memory card when this light is on. Diagram 3, Image Screen shot of a COM2-Tera Term VT window. Boot screen for a Cisco device with the following line highlighted. SYSTEM INIT: INSUFFICIENT MEMORY TO BOOT THE IMAGE! 9.2.3 - Troubleshooting Cable and Device Port Errors Three Diagram Diagram 1, Image R1#show ip interface brief Interface IP-Address OK? Method Status Protocol FastEthernet0/0 192.168.1.1 YES manual up up FastEthernet0/1 unassigned YES manual administratively down down Serial0/0/0 192.168.2.1 YES manual up up Serial0/0/1 unassigned YES manual administratively down down Vlan1 unassigned YES manual administratively down down Diagram 2, Image Media Problem Excessive Noise Step 1: Use the show interface command to determine the status of the Ethernet interfaces. The presence of many CRC errors but not many collisions is an indication of excessive noise. Step 2: inspect the cables for damage or sources of interference. Step 3: Verify that the correct cable and termination standard is in use for the speed of the interface. Step 4: if using 1000BASE-TX, make sure that Category 5e or above cabling is being used. Excessive Collisions Step 1: use the show interface command to check that rate of collisions. The total number of collisions with respect to the total number of output packets should be 1% or less. Step 2: use a TDR to find any damaged cables. Excessive Runt Frames Step 1: in a shared Ethernet environment, runt frames are almost always caused by collisions. If the collision rate is high, see the ?Excessive collisions? problem. Step 2: If runt frames occur when collision rates are not high or in switched Ethernet environment, they are the result of bad software on a NIC. Step 3: Use a protocol analyzer to try to determine the source address of the runt frames. Late Collisions Step 1: Use protocol analyzer to check for late collisions. Late collisions should never occur in a property designed Ethernet network. They usually occur when Ethernet cables are too long or when a duplex mismatch occurs. Step 2: Verify that the diameter of the network is within specification. Diagram 3, Hands-on Lab 9.2.4 - Troubleshooting LAN Connectivity Issues Four Diagrams Diagram 1, Image Image of the rear of a switch Catalyst 2950 series indicating the following components: * System LED * Redundant Power Supply LED * Mode Button * Port Mode LEDs * Port Status LEDs Diagram 2, Image Error message indicating that a duplex mismatch is detected. Jun 2 11:16:45 %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet6/2 (not half duplex), with TBA04251336 3/2 (half duplex). Show output indicating that duplex and speed settings were set to auto negotiate. Switch# sh interfaces fas 6/1 status Portname Status Vlan Duplex Speed type Fa6/1 notconnect 1 auto auto 10/100BaseTX Diagram 3, Packet Tracer Exploration Diagram 4, Hands-on Lab 9.2.5 - Troubleshooting WAN Connectivity Issues Four Diagrams Diagram 1, Image The image shows a typical WAN topology using the following devices: * Access Server * WAN Switch * Core Routers * CSU/DSU * Router * Cable Modem * DSL Modem * Dialup Modems Diagram 2, Image Serial x is down, line protocol is down (DTE) Possible Problem: * Indicates that the router is not sensing a carrier detect signal. * Telephone company problem ? Line is down or not connected to CSU/DSU. * Faulty or incorrect cabling. * Hardware failure (CSU/DSU) To Troubleshoot: Step 1: Check the LEDs on the CSU/DSU to see whether the light is active. Step 2: Verify that you are using the proper cable and interface. Step 3: Contact your leased-line or other carrier service to see whether there is a problem. Step 4: Replace the serial interface module with a known good module. Step 5: Replace the CSU/DSU with a known good device. Serial x is up, line protocol is down (DTE) Possible Problem: * Local or remote router is misconfigured. * Keepalives are not being sent by the remote router. * Failed remote CSU or DSU. * Failed local or remote CSU/DSU. To Troubleshoot: Step 1: Put the modem, CSU, or DSU in local loopback mode, and use the show interface serial command to determine whether the line protocol comes up. If the line protocol comes up, a telephone company problem or a failed remote router is probably the cause. Step 2: If the problem appears to be on the remote end, repeat Step 1 on the remote modem, CSU, or DSU. Step 3: Verify all cabling. Make certain that the cable is attached to the correct interface, the correct CSU/DSU, and the correct telephone company network termination point. Step 4: Verify that the encapsulation is correct on both ends of the circuit. Step 5: If the line protocol does not come up in local loopback mode and if there is no encapsulation mismatch, replace failed hardware. Serial x is up, line protocol is down (DCE) Possible Problem: * Missing clockrate interface configuration command. * Failed local or remote CSU/DSU. * Failed or incorrect cable. * Router hardware failure. To Troubleshoot: * Step 1: Add the clockrate interface configuration command on the serial interface. * Step 2: Verify that the correct cable is being used. * Step 3: If the line protocol is still down, there is a possible hardware failure or cabling problem. * Step 4: Replace faulty parts as necessary with known good equipment. Serial x is up, line protocol is up (looped) Possible Problem: * A loop exists in circuit. The sequence number in the keepalive packet changes to a random number when a loop is detected initially. If the same random number is returned over the link, a loop exists. To Troubleshoot: Step 1: Use the show running-config privileged EXEC command. This will enable you to look for any loopback interface configuration command entries. Step 2: If you find a loopback interface configuration command entry, use the no loopback interface configuration command to remove the loop. Step 3: If you do not find the loopback interface configuration command, examine the CSU/DSU to determine whether it is configured in manual loopback mode. If it is, disable manual loopback. Step 4: Reset the CSU/DSU and inspect the line status. If the line protocol comes up, no other action is needed. Step 5: If the CSU/DSU is not configured in manual loopback mode, contact the leased-line or other carrier service for line troubleshooting assistance. Serial x is up, line protocol is down (disabled) Possible Problem: * High error rate because of telecommunications service problem. * CSU/DSU hardware problem. * Bad router hardware. To Troubleshoot: Step 1: Contact the telecommunications service provider. Step 2: Loop CSU/DSU (DTE loop). If the problem continues, there is likely a hardware problem. If the problem does not continue, the problem is likely with the telephone company. Step 3: Swap out bad hardware as required (CSU/DSU, switch, interface module, or remote router). Serial x is administratively down, line protocol is down Possible Problem: * Router configuration includes the shutdown interface configuration command. * Duplicate IP address. To Troubleshoot: Step 1: Check the configuration for the shutdown command. Step 2: Use the no shutdown interface configuration command to remove the shutdown command. Step 3: Verify that there are no identical IP addresses using the show running-config privileged EXEC command or the show interface EXEC command. Step 4: If there are duplicate addresses, resolve the conflict by changing one of the IP addresses. Diagram 3, Packet Tracer Exploration Diagram 4, Hands-on Lab 9.2.6.0 - Certification Study Guide Single Diagram Diagram 1, Hands-on Lab CCENT Study Guide Please see your instructor for further information. 9.3 - Troubleshooting Layer 3 IP Addressing Issues 9.3.1 - Review of Layer 3 Functionality and IP Addressing Four Diagrams Diagram 1, Image Layer 2 Multiple Layer 2 Protocols Different protocols may be in use for different media. A network comprising of hosts, routers, satellite dish transmitting to satellites and wireless routers transmitting to laptops. Data Link Layer protocols govern how to format a frame for use on different media. At each hop along the path, an intermediary device accepts frames from one medium, decapsulates the frame and then forwards the packets in a new frame. The headers of each frame are formatted for the specific medium that it will cross. Layer 3 Single Layer 3 Protocol The same Network Layer protocol can be used across different media. A network comprising of hosts, routers, satellite dish transmitting to satellites and wireless routers transmitting to laptops. Network Layer protocols govern the format of the packet headers as well as the format of the network and host addressing. Although the frame format may change every time the physical media changes, the format of the Network Layer packet remains the same. Diagram 2, Image Subnetting On a 24 bits network portion address three bits are borrowed from the host portion to provide eight subnets. 192.168.1.0 (/24) Address: 11000000.10101000.00000001.00000000 255.255.255.0 Mask: 11111111.11111111.11111111.00000000 0 192.168.1.0 (/27) Address: 11000000.10101000.00000001.00000000 255.255.255.0 Mask: 11111111.11111111.11111111.11100000 1 192.168.1.32 (/27) Address: 11000000.10101000.00000001.00100000 255.255.255.0 Mask: 11111111.11111111.11111111.11100000 2 192.168.1.64 (/27) Address: 11000000.10101000.00000001.01000000 255.255.255.0 Mask: 11111111.11111111.11111111.11100000 3 192.168.1.96 (/27) Address: 11000000.10101000.00000001.01100000 255.255.255.0 Mask: 11111111.11111111.11111111.11100000 4 192.168.1.128(/27) Address: 11000000.10101000.00000001.10000000 255.255.255.0 Mask: 11111111.11111111.11111111.11100000 5 192.168.1.160 (/27) Address: 11000000.10101000.00000001.10100000 255.255.255.0 Mask: 11111111.11111111.11111111.11100000 6 192.168.1.192 (/27) Address: 11000000.10101000.00000001.11000000 255.255.255.0 Mask: 11111111.11111111.11111111.11100000 7 192.168.1.224 (/27) Address: 11000000.10101000.00000001.11100000 255.255.255.0 Mask: 11111111.11111111.11111111.11100000 Addressing Scheme Addressing Scheme: Example of 8 networks Subnet: 0 Network Address: 192.168.1.0 Host Range: 192.168.1.1 - 192.168.1.30 Broadcast Address: 192.168.1.31 Subnet: 1 Network Address: 192.168.1.32 /27 Host Range: 192.168.1.33 - 192.168.1.62 Broadcast Address: 192.168.1.63 Subnet: 2 Network Address: 192.168.1.64 /27 Host Range: 192.168.1.65 - 192.168.1.94 Broadcast Address: 192.168.1.95 Subnet: 3 Network Address: 192.168.1.96 /27 Host Range: 192.168.1.97 - 192.168.1.126 Broadcast Address: 192.168.1.127 Subnet: 4 Network Address: 192.168.1.128/27 Host Range: 192.168.1.129 - 192.168.1.158 Broadcast Address: 192.168.1.159 Subnet: 5 Network Address: 192.168.1.160/27 Host Range: 192.168.1.161 - 192.168.1.190 Broadcast Address: 192.168.1.191 Subnet: 6 Network Address: 192.168.1.192/27 Host Range: 192.168.1.193 - 192.168.1.222 Broadcast Address: 192.168.1.223 Subnet: 7 Network Address: 192.168.1.224/27 Host Range: 192.168.1.225 - 192.168.1.254 Broadcast Address: 192.168.1.255 Diagram 3, Activity Given the network address and the subnet mask, define the range of hosts, the broadcast address, and the next network address. Network Address in decimal: 10.55.119.128 Subnet Mask in decimal: 255.255.255.128 Network address in binary: 00001010.00110111.01110111.10000000. Subnet Mask in binary: 11111111.11111111.11111111.10000000 First Usable Host IP Address in decimal: (1st octet? 2nd octet? 3rd octet? 4th octet?) Last Usable Host IP Address in decimal: (1st octet? 2nd octet? 3rd octet? 4th octet?) Broadcast Address in decimal: (1st octet? 2nd octet? 3rd octet? 4th octet?) Next Network Address in decimal: (1st octet? 2nd octet? 3rd octet? 4th octet?) Help The range of host addresses within a subnet is dependent upon the number and location of host bits. Class C example: 192.168.1.32 / 27 Written in decimal: IP: 11000000.10101000.00000001.00100000 SM: 11111111.11111111.11111111.11100000 According to the subnet mask (SM), the first 27 bits of the IP address are part of the network, leaving 5 bits to indicate a unique host. A host IP address cannot have all 1s or all 0s in the host portion. All 1s in the host bits is the broadcast address for that subnet. First avail IP: 11000000.10101000.00000001.00100001 192. 168. 1. 33 Last avail IP: 11000000.10101000.00000001.00111110 192. 168. 1. 62 Broadcast IP: 11000000.10101000.00000001.00111111 192. 168. 1. 63 Class A example: 10.10.64.0 / 19 Written in decimal: IP: 00001010.00001010.01000000.00000000 SM: 11111111.11111111.11100000.00000000 According to the subnet mask, the first 19 bits of the IP address are part of the network, leaving 13 bits to indicate a unique host. A host IP address cannot have all 1s or all 0s in the host portion. All 1s in the host bits is the broadcast address for that subnet. First avail IP: 00001010.00001010.01000000.00000001 10. 10. 64. 1 ( 64 + 0) Last avail IP: 00001010.00001010.01011111.11111110 10. 10. 95. 254 ( 64 + 31) Broadcast IP: 00001010.00001010.01011111.11111111 10. 10. 95. 255 ( 64 + 31) Diagram 4, Packet Tracer Exploration 9.3.2 - IP Design and Configuration Issues Four Diagrams Diagram 1, Image Image depicts a hierarchical IP Addressing scheme. The gateway router which connects to the internet is on a network with a 16 bit network portion. The three routers coming from the gateway router have 22 bit network portion addressing schemes. The networks which connect to these routers all have 24 bit network portion addresses. Diagram 2, Image Configuration Error Messages R1(config)#interface FastEthernet0/1 R1(config-if)#ip address 192.168.1.2 255.255.255.252 192.168.1.0 overlaps with FastEthernet0/0 R1(config)#no shutdown 192.168.1.0 overlaps with FastEthernet0/0 FastEthernet0/1: incorrect IP address assignment Show Output R1(config)#show ip interface brief FastEthernet1 192.168.1.2 YES manual administratively down down Diagram 3, Image Two LAN separated by a router. One LAN contains host H1 and H1 which connect to a switch which connects to the router which separates the two LANs. The other LAN contains a two server SV1 and unnamed, which connect to a switch which connects to the router which separates the two LANs. The router also connects to the internet. Issue 1 H2 (192.168.0.42/27) says ?I requested a web page from SV1, but have not received it.? SV1 (192.168.0.5/24) in the other LAN says ?192.168.0.42 is on my 192.168.0.0/24 network, but has not responded to my ARP request; therefore I cannot respond.? A Server is Only Accessible by Hosts on the Same Subnet A server on one of the subnets is manually configured using the default /24 network prefix instead of the /27. This misconfiguration causes the server to determine that all hosts on the various subnets are on the same Layer 3 network that the server is on. The server does not send any traffic to the default gateway for any hosts on the /27 subnets. Check server configurations if this symptom occurs. Issue 2 H1 (192.168.0.43/24) says ?I need a web page from IP address 200.200.1.1. I have forwarded my request to the gateway.? H2 (192.168.0.41/14) says ?I need a web page from SV1. SV1 is on my network. I can ARP for the MAC address.? Hosts Get Responses from Internet Servers, but Not Servers on Another Subnet A host or group of hosts are configured with a /24 subnet mask that causes an overlap with the server network subnet addresses. Each host correctly determines that Internet addresses are not on their local Layer 3 network, and sends the traffic to the default gateway. The hosts incorrectly determine that internal server addresses are on their local network, and use ARP to attempt to get the server MAC addresses. Check DHCP server configurations and host configurations when this symptom is evident. A network sniffer can be used to show the ARP frames. Issue 3 H2 (192.168.0.42/24) says ?According to the IP information, the DNS server is on my local network, but I am unable to reach the DNS server to resolve hostnames.? Hosts are Unable to Get Responses from Internet Servers or Servers on Another Subnet, Using Hostnames A host or group of hosts are configured with a /24 subnet mask that causes an overlap with the server network subnet addresses, including the DNS server. Subnet mask errors on hosts do not usually affect Internet connectivity; however, if the subnet mask error causes the host subnet to overlap the subnet containing the DNS server, the host(s) will not be able to contact the DNS server. Without DNS, no IP addresses can be resolved and all services that rely on DNS cannot be accessed. Check host and DNS configurations if unable to access the Internet. Issue 4 The router between the two subnets says ?I have received a packet for destination 192.168.0.51, but that does not match any route in my routing table. I cannot forward this packet.? Some Hosts Can Get Responses from Internet Servers and Servers on Other Subnets, but Others Cannot The subnet mask configuration error occurs on a router interface that serves as a default gateway for one of the /27 subnets. If the router interface is incorrectly configured with a /28 subnet mask, the route entered in the routing table will not include all hosts on the /27 subnet. Hosts with addresses on the lower portion of range that are within the /28 subnet IP address boundaries will be able to send and receive through the router. Those with address in the top half of the range can send packets to remote destinations, but when the responses return, the router does not have a route to the destination IP addresses. Always verify all connected routes in the routing table using the show IP route command. Diagram 4, Simulation GUI IP Address Configuration Please see your instructor for further information. 9.3.3 - IP Address Planning and Allocation Issues Three Diagrams Diagram 1, Image R1#show ip dhcp binding Binding from all pools not associated with VRF: IP address Client-ID/ Lease expiration Type Hardware address User name 192.168.10.10 100.e018.5bdd.35 Oct 03 2007 06:14 PM Automatic 192.168.10.11 100.d0d0.d817.e6 Oct 03 2007 06:18 PM Automatic Diagram 2, Activity Please see your instructor for further information. Diagram 3, Hands-on Lab 9.3.4 - DHCP and NAT Issues Five Diagrams Diagram 1, Image Screen shot of a Windows cmd.exe widow showing the IPConfig /all command. Diagram 2, Image DHCP Problem Router R1 connects to a WAN via DCE. R1 also connects to network 192.168.10./24 via Fa0/0 with the link address 192.168.10.1/24 to switch S1s Fa0/1 port. S1 (192.168.10.2/24) connects via Fa0/2 to host PC1 (192.168.10.10/24). R1 also connects to network 192.168.11.0/24 via Fa0/1 to switch S2s Fa0/1 port with the link address 192.168.11.1/24. S2 (192.168.11.2/24) connects via Fa0/24 to DHCP server (192.168.11.5/24). PC1 says ?Looking for a DHCP server ...? Router 1 says ?Sorry, I can?t forward any broadcasts outside of your network subnet ...? Host Problem C:\Documents and Settings\Administrator>ipconfig /release Windows IP Configuration Ethernet adapter Local Area Connection: Connection-specific DNS Suffix . : IP Address. . . . . . . . . . . . : 0.0.0.0 Subnet Mask . . . . . . . . . . . : 0.0.0.0 Default Gateway . . . . . . . . . : C:\Documents and Settings\Administrator>ipconfig /renew Windows IP Configuration An error occurred while renewing interface Local Area Connection : unable to contact your DHCP server. Request has timed out. C:\Documents and Settings\Administrator> ÿ Relay Config Router R1 connects to a WAN via DCE. R1 also connects to network 192.168.10./24 via Fa0/0 with the link address 192.168.10.1/24 to switch S1s Fa0/1 port. S1 (192.168.10.2/24) connects via Fa0/2 to host PC1 (192.168.10.10/24). R1 also connects to network 192.168.11.0/24 via Fa0/1 to switch S2s Fa0/1 port with the link address 192.168.11.1/24. S2 (192.168.11.2/24) connects via Fa0/24 to DHCP server (192.168.11.5/24). R1# config t R1(config)# interface Fa0/0 R1(config-if)# ip helped-address 192.168.11.5 R1(config)# end Host Renew C:\Documents and Settings\Administrator>ipconfig /release Windows IP Configuration Ethernet adapter Local Area Connection: Connection-specific DNS Suffix . : IP Address. . . . . . . . . . . . : 0.0.0.0 Subnet Mask . . . . . . . . . . . : 0.0.0.0 Default Gateway . . . . . . . . . : C:\Documents and Settings\Administrator>ipconfig /renew Windows IP Configuration Ethernet adapter Local Area Connection: Connection-specific DNS Suffix . : IP Address. . . . . . . . . . . . : 192.168.10.11 Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : 192.168.10.1 C:\Documents and Settings\Administrator> ÿ Diagram 3, Image Access-list 1 permit 192.168.0.0 0.0.255.255 !-Defines which addresses are eligible to be translated Ip nat pool NAT-POOL2 209.165.200.266 209.165.20.240 !-Defines a pool of addresses named NAT-POOL2 to be used in NAT translation Ip nat inside source list 1 pool NAT-POOL2 overload !-Binds the NAT pool with ACL1 Interface serial 0/0/0 Ip nat inside !-indentifies interface Serial 0/0/0 as an inside NAT interface Interface serial 0/1/0 Ip nat outside !-indentifies interface Serial 0/1/0 as an outside NAT interface Diagram 4, Image NAT Overload Access-list 1 permit 192.168.10.0 0.0.0.0.255 Ip nat inside source list 1 interface serial 0/1/0 overload Interface fastethernet0/0 Ip nat inside Interface serial 0/1/0 Ip nat outside NAT Translations R2 #show ip nat translations Pro Inside global Inside local t cp 209.165.200.225:16642 192.168.10.10:16642 t cp 209.165.200.225:62452 192.168.10.11:62452 Outside local 209.165.200.254:80 209.165.200.254:80 Outside global 209.165.200.254:80 209.165.200.254:80 R2 #show ip nat translations verbose Pro Inside global Inside local Outside local Outside global t cp 209.165.200.225:16642 192.168.10.10:16642 209.165.200.254:80 209.165.200.254:80 create 00:01:45, use 00:01:43 timeout :86400000, left 23:58:16, Map-Id (In) :1, flags: extended, use count: 0, entry- id: 4, 1c_entries : 0 tcp 209.165.200.225:62452 192.168.10.11:62 452 209.165.200.254:80 209.165.200 .254:80 create 00:00:37, use 00:00:35 timeout:86400000, left 23:59:24, Map-Id (In): 1, flags: extended, use count : 0, entry-id : 5, lc_entries: 0 R2# Cleared NAT R2#clear ip nat translation * R2#show ip nat translations R2# Diagram 5, Packet Tracer Exploration 9.3.5 - Certification Study Guide Single Diagram Diagram 1, Hands-on Lab CCENT Study Guide Please see your instructor for further information. 9.4 - Troubleshooting Layer 3 Routing Issues 9.4.1 - Layer 3 Routing Issues Four Diagrams Diagram 1, Image 7 Application 6 Presentation 5 Session 4 Transport 3 Network * Symptoms o Network failure o Network performance below baseline 2 Data Link 1 Physical Diagram 2, Tabular Route Source: Connected Administrative Distance: 0 Default Metric(s): 0 Route Source::EIGRP Summary Route Administrative Distance: 5 Default Metric(s): 0 Route Source: Static Administrative Distance: 1 Default Metric(s): 0 Route Source: External BGP Administrative Distance: 20 Default Metric(s): Value assigned by Admin Route Source: Internal EIGRP Administrative Distance: 90 Default Metric(s): Bandwidth Delay Route Source: IGRP Administrative Distance:100 Default Metric(s): Bandwidth, Delay Route Source: OSPF Administrative Distance: 110 Default Metric(s): Link cost (bandwidth) Route Source: IS-IS Administrative Distance: 116 Default Metric(s): Link cost (Value assigned by admin) Route Source: RIP Administrative Distance: 120 Default Metric(s): Hop count Route Source: External EIGRP Administrative Distance: 170 Default Metric(s): Route Source: Internal BGP Administrative Distance: 200 Default Metric(s): Value assigned by Admin Diagram 3, Screen shot of an Edit Router C Window with the following highlighted. R-RIP Gateway of last resort is 192.168.1.2 to network 0.0.0.0 Directly Connected Route C 172.16.0.0/16 is directly connected, Fast Ethernet 0 10.0.0.0/24 is subnetted, 1 subnets Static Route S 10.10.10.0 [1/0] via 192.168.1.2 Dynamically Updated Route R 192.168.2.0/24 [120/1] via 192.168.1.2, 00:00:23 Default Route S* 0.0.0.0/0 [1/0] via 192.168.1.2 Gateway of last resort is 192.168.1.2 to network 0.0.0.0 Diagram 4, Packet Tracer Exploration Applying Routing Table Principles Please see your instructor for further information. 9.4.2 - Dynamic Routing Errors Four Diagrams Diagram 1, Image Router 1 is part of a complex network which uses VLSM and static routes. the rip portion displaying when the show running-config command is issued on router 1. Router RIP Version 2 Network 172.30.0.0 Network 209.165.200.0 No auto-summary ! Diagram 2, R1 is connected via S0/0/0 to R2s S0/0/0 with the link address 172.20.1.0/30. R1 is connected via Fa0/0 to network 192.168.1.0/24. R2 is connected via Fa0/0 to network 192.168.2.0/24. show ip protocols Highlighted portion of output for this command: Default version control: send version 2, receive version 2 Routing for Networks: 172.20.0.0 192.168.1.0 show running-config description LAN gateway for 192.168.1.0 ip address 192.168.1.1 255.255.255.0 duplex auto ip address 172.20.1.1 255.255.255.252 no fair-queue ! Network 172.20.0.0 Network 192.168.1.0 ! Banner motd #Unauthorized use prohibited# ! show interfaces MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, Auto-duplex, Auto speed, 100BaseTX/FX show ip interface Multicast reserved groups joined: 224.0.0.9 Multicast reserved groups joined: 224.0.0.9 show ip route No highlighted section. debug ip rip *Sep 12 21:09:16.399:RIP: received v2 update from 172.20.1.2 on Serial0/0/0 Diagram 3, Packet Tracer Exploration Diagram 4, Hands-on Lab 9.4.3.0 - Certification Study Guide Single Diagram Diagram 1, Hands-on Lab CCENT Study Guide Please see your instructor for further information. 9.5.0 - Troubleshooting Layer 4 and Upper Layer Issues 9.5.1 - Layer 4 Traffic Filtering Errors Two Diagrams Diagram 1, Image Transport Layer Problems 7 Application 6 Presentation 5 Session 4 Transport * Symptoms o Intermittent network problems o Security problems o Trouble reaching some web sites or other network-based applications and services. 3 Network 2 Data Link 1 Physical Well-known Ports Destination port number: 20 Abbreviation: FTP Data Definition: File Transfer Protocol (for data transfer) Destination port number: 21 Abbreviation: FTP Control Definition: File Transfer Protocol (to establish connection) Destination port number: 23 Abbreviation: TELNET Definition: TELetype NETwork Destination port number: 25 Abbreviation: SMTP Definition: Simple Mail Transfer Protocol Destination port number: 53 Abbreviation: DNS Definition: Domain Name Service Destination port number: 67 Abbreviation: DHCP v4 Client Definition: Dynamic Host Configuration Protocol (Client) Destination port number: 68 Abbreviation: DHCP v4 Server Definition: Dynamic Host Configuration Protocol (Server) Destination port number: 69 Abbreviation: TFTP Definition: Trivial File Transfer Protocol Destination port number: 80 Abbreviation: HTTP Definition: Hypertext Transfer Protocol Destination port number: 110 Abbreviation: POP3 Definition: Post Office Protocol (version 3) Destination port number: 137 Abbreviation: NBNS Definition: Microsoft NetBIOS Name Service Destination port number: 143 Abbreviation: IMAP4 Definition: Internet Message Access Protocol (version 4) Destination port number: 161 Abbreviation: SNMP Definition: Simple Network Management Protocol Destination port number: 443 Abbreviation: HTTPS Definition: Hypertext Transfer Protocol Secure Diagram 2, Activity Match the protocol name to the port number. Ports A. 21 B. 53 C. 161 D. 67 E. 110 F. 23 G. 80 H. 25 I. 143 Protocols 1. FTP 2. Telnet 3. SMTP 4. HTTP 5. POP3 6. IMAP4 7. DNS 8. DHCP 9. SNMP 9.5.2 - Troubleshooting Upper Layer Problems Four Diagrams Diagram 1, Image OSI Reference Model 7 Application, 6 Presentation, 5 Session: (HTTP, Telnet, FTP, TFTP, SMTP, POP3, IMAP4, SNMP, NTP, DNS, SSL, SSH) There are all TCP/IP Application Layer protocols. Diagram 2, Image Step 1. Ping the host default gateway If both the host and the server can successfully ping their default gateways, Layer 1 and Layer 2 services are functioning properly and Layer 3 local network connectivity exists. If the ping to the local default gateway address fails, troubleshoot Layers 3, 2, and 1 to locate the source of the problem. Step 2. Verify end-to-end connectivity Ping or telnet from the host to a remote server or networking device. If successful, Layer 3 routing is operating correctly. When Layers 1, 2 and 3 are functioning properly, the issue must exist at a higher layer. If this ping is unsuccessful, it is necessary to troubleshoot the routing, NAT and firewall configurations to ensure proper packet delivery. Step 3. Verify the routing configuration Ensure that the routing configuration is correct and that routes are updating as expected. If the routing table does not contain expected routes, troubleshoot and fix the routing configuration and attempt Step 2 again. If still unable to ping, check the NAT configuration. Step 4. Ensure that NAT is working correctly When there is a problem reaching services on a remote network, such as over the Internet, NAT may not be functioning correctly. Use the show ip nat translations command to verify that translations are occurring. Clear the NAT translations with the clear ip nat translation * command and try to access the external resource again. If still not successful, check the configuration of the inside and outside interfaces. When the NAT configuration has been verified, attempt Step 2 again. If still unable to ping, check for firewall filter rules. Step 5. Check for firewall filter rules Even though there is IP connectivity between a source and a destination, problems may still exist for a specific upper layer protocol, such as FTP, HTTP, or Telnet. These protocols ride on top of the basic IP transport but are subject to protocol-specific problems relating to packet filters and firewalls. Verify that the necessary ports are permitted on all firewalls. Diagram 3, Image 7 Application, 6 Presentation, 5 Session * Symptoms: o User complains about slow application performance o Application error message o Unable to access application services, such as FTP o Unable to access Web services Diagram 4, Image A screen shot of a Mac server not found window. 9.5.3 - Using Telnet to Check Upper Layer Connectivity Two Diagrams Diagram 1, Image Telnet client with a virtual terminal connection connected via the internet to a telnet server. Telnet provides a way to use a computer, connected via the network, to access a network device as if the keyboard and monitor were directly connected to the device. Diagram 2, Hands-on Lab 9.5.4 - Certification Study Guide Single Diagram Diagram 1, Hands-on Lab CCENT Study Guide Please see your instructor for further information. 9.6 - Preparing for Cisco Certification 9.6.1 - Knowledge, Skills and Abilities Two Diagrams Diagram 1, Take ICND1 640-822 Exam Discovery 1 & 2 and pass that to become CCENT Certified. Then Take ICND2 640-816 Exam Discovery 3 & 4 and become CCNA Certified. Take CCNA 640-802 Discovery 1 ? 4, pass that and become CCNA Certified. Diagram 2, Knowledge Knowledge statements are typically factual or procedural in nature. They are relate directly to the performance of a function. Skills Skill statements refer to the capability to manually, verbally, or mentally manipulate data or things to achieve a desired result. Skills can be measured by a performance test where quantity and quality of performance are tested, usually within an established time limit. Examples of skill related tasks include skill in typing or skill in operating a vehicle. Abilities Ability statements refer to the power to perform an observable activity at the present time. This means that abilities have been proven through activities or behaviors that are similar to those required on the job. An example is the ability to plan and organize work. 9.6.2 - Networking Knowledge, Skills and Abilities Five Diagrams Diagram 1, Image Post it notes with the following messages: * In a RIP network, what is the maximum number of hops a packet can take before a destination becomes unreachable? * Which routing protocols use a distance vector algorithm? * How does a switch determine which port to use to reach a destination? * Where is the startup configuration stored on a Cisco router? Diagram 2, Image This sample question is designed to test the IP addressing skills of the candidate. It also requires the candidate to be familiar with configuring Cisco IOS software. Refer to the exhibit. Which Cisco IOS command will assign the first update IP address in the subnet work to FastEthernet0/1 of RTA? (Picture referred to as exhibit displayed here) A. RTA(config-if)#ip address 172.18.13.1 255.255.254.0 B. RTA(config-if)#ip address 172.18.14.1 255.255.252.0 C. RTA(config-if)#ip address 172.18.14.1 255.255.255.252 D. RTA(config-if)#ip address 172.18.16.1 255.255.252.0 E. RTA(config-if)#ip address 172.18.16.1 255.255.252.252 F. RTA(config-if)#ip address 172.18.16.229 255.255.255.252 Diagram 3, Image Task: Configure RIP V2 to route network traffic Information needed * Steps to configure RIPv2 routing 1. Log into the router 2. Enter privileged mode 3. Enter configuration mode 4. Enable RIP 5. Enable version 2 6. Configure a network statement for each connected network that participates in RIP. * Cisco IOS commands to enable RIPv2 routing 1. Config t 2. Router rip 3. Version 2 4. Network [address] 5. Copy running-config startup-config * Network addresses for each connected network * Methods to verify if RIPv2 is configured correctly and working. 1. Use show running-configuration command 2. Use show ip route command 3. Ping from a host to a remote ip address on another network 4. Trace the route through the router to a remote ip address 5. Use debug to verify the RIPv2 routing updates are being sent and received. Possible incorrect outcomes if I do no posses the necessary knowledge * I cannot enter configuration mode to being the configuration * I forgot to configure version 2 or add the network statement * I do not configure all the networks * I enter the wrong ip address information * I cannot verify if RIPv2 is operating correctly Possible symptoms of problems * Cannot ping hosts on other networks * Cannot trace route through the router * No route appear in routing table of router Diagram 4, Activity Identify knowledge tasks, skills related tasks, and abilities. Tasks Troubleshoot a non-functioning network Calculate an IP subnet Configure an IP address on a router interface Plan the implementation of a new router List two distance vector routing protocols Build a Category 5 crossover cable Design an IP address scheme Explain the meaning of the term NAT Skills and Abilities Knowledge Ability Skill Diagram 5, Hands-on Lab 9.6.3 - Making the Commitment Two Diagrams Diagram 1, Image Course pyramid offered by Cisco. (bottom to top) CCENT CCNA CCNP CCIE Diagram 2, Image Image is not relevant. 9.6.4 - Creating a Plan Three Diagrams Diagram 1, Image Checklist * Obtaining and distributing study materials * Scheduling lab time * Ensuring all necessary supplies are available * Keeping track of the group progress * Finding answers to problems Diagram 2, Image Image is not relevant. Diagram 3, Screen shot of the home page of the CCNA Prep Center. 9.6.5 - Practicing Test Taking Five Diagrams Diagram 1, Image Image is not relevant. Diagram 2, Image Image is not relevant. Diagram 3, Hands-on Lab Exploring the CCNA Prep Center Please see your instructor for further information. Diagram 4, Image Several windows open on a desktop the following information is provided about these windows. * This window displays a terminal emulation screen. It is used to enter CLI commands to make changes to device configuration and to display output. * This window displays the topology of the network and provides additional context for the simulation. * This window provides instructions on how to complete the simulation. * These are control buttons that open and activate the various simulation windows. Diagram 5, Packet Tracer Exploration 9.6.6 - Certification Study Guide Two Diagrams Diagram 1, Hands-on Lab Preparing for the ICND1 Exam Please see your instructor for further information. Diagram 2, Hands-on Lab CCENT Study Guide Please see your instructor for further information. 9.7 - Chapter Summary 9.7.1 - Summary Single Diagram Diagram 1, Slideshow Slide 1 OSI Model Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer TCP/IP Model Application Transport Internet Network Access * Each layer of the OSI or TCP/IP model has specific functions and protocols. Knowledge of the features, functions and devices of each layer, and how each layer relates to the layers around it, help a network technician to troubleshoot more efficiently. * The upper layers (5-7) of the OSI model deal with specific application functionality and are generally implemented only in software. The lower layers (1-4) of the OSI model handle data transport and physical networking functions. * There are three main troubleshooting approaches when using network models: o Top-down o Bottom-up o Divide-and-conquer Slide 2 Tools that assist with network trouble shooting include: * Network Diagrams and Documentation * Network Documentation and Baseline Tools * Network Management Systems * Knowledge Bases * Protocol Analysers Sometimes failures in the lower layer of the OSI model cannot be easily identified with software tools. In these instances, it may be necessary to use hardware troubleshooting tools, such as cable testers, multimeters, and network analyzers. Slide 3 Image shows the boot sequence of a router. * The Physical and the Data link Layers encompass both hardware and software functions. * The Physical layer, or Layer 1, is responsible for the physical and electrical specifications for the transmission of bits from one host to another over the physical medium, either wired or wireless. * Layer 1 Problems include: o Cable type, length and termination problems o Duplex mismatches o Interfaces and noise that disrupts transmissions o Device hardware and boot errors * Router interface errors are often the first symptom of Layer 1 and Layer 2 cabling or connectivity errors. * Devices LEDs provide valuable troubleshooting information that can be used to identify the cause of connectivity issues. Slide 4 Screen shot of the show ip interface brief command. * The Data Link Layer, or Layer 2, specifies how the data is formatted for transmission over the network media. It also regulates how access to the network is granted. Layer 2 provides the link between the Network Layer software functions and the Layer 1 hardware for both LAN and WAN applications. * Layer 2 Problems include: o Encapsulation mismatches o No keepalives generated or received o Timing problems on WAN connections * The show version , show interfaces and show interface brief commands provide troubleshooting information to isolate and identify Layer 1 and Layer 2. Slide 5 Sample Subnet Addressing Scheme. * The primary functions implemented at Layer 3 of the OSI model are network addressing and routing. * Poorly designed and configured IP addressing schemes, especially overlapping subnet addresses, account for a large number of network performance problems. * Overlapping subnets can be caused by careless address assignment or by improperly configured subnet masks on devices. * Problems obtaining an IP address from a DHCP server can cause PC clients to automatically configure an address on the 169.254.0.0 network. * NAT configuration and operation issues can cause Internet sites to be unreachable from the privately addressed LAN. Slide 6 Screen shot of the show ip route command. * Most networks have a number of different types of routes, including a combination of static, dynamic, and default routes. * Problems with routing can be the result of manual route entry errors, routing protocol configuration and operation errors, or failures at lower layers of the OSI model. * The primary tool to use when troubleshooting Layer 3 routing problems is the show ip route command. The routing table consists of route entries from the following sources: o Directly connected networks o Static routes o Dynamic routing protocols * Problems that occur with RIPv2 routing include: o Version not specified causing version mismatch between routers. o Misconfigured or missing network statements o Improperly configured interface IP addresses Slide 7 Image shows a virtual terminal setup. * Layer 4 is responsible for transporting data packets and specifies the port number used to reach specific applications. * Firewall and port filtering rules that permit or deny the incorrect ports can cause needed services to be unreachable from client computers. * Upper Layer services include DNS name resolution, encryption and compression. Errors occurring with these functions can cause end-user applications to be unusable. * The Windows command nslookup can provide information to assist with troubleshooting DNS failures. Slide 8 Shows the paths to CCNA certification. * The Cisco Certified Entry Networking Technician (CCENT) certification validates the skills required for entry-level network support positions, the starting point for many successful careers in networking. * To obtain CCENT certification, a candidate must pass the ICND1 (640-822) examination which tests the ability to install, operate, and troubleshoot a small branch office network. * Cisco certifications measure and validate the networking skills of an individual based on how they interact with Cisco networking devices. Many exam tasks require the interpretation of Cisco IOS command output, especially the output of the various show commands. * Just like installing a network for a customer, exam preparation is more successful if it is broken down into a series of smaller steps: 1. Making the commitment. 2. Creating a plan. 3. Practicing test taking.