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Transcript
Network Troubleshooting Chapter 15 Objectives • Describe appropriate troubleshooting tools and their functions • Analyze and discuss the troubleshooting process • Tackle a variety of troubleshooting scenarios Overview Introduction to Network Troubleshooting Three Parts to Chapter 15 • Troubleshooting Tools • The Troubleshooting Process • Troubleshooting Scenarios Troubleshooting Tools • Hardware Tools – – – – – – – – – Cable Tester, TDR, and OTDR Certifiers Voltage Event Recorder/Temperature Monitor Protocol Analyzer Cable Stripper/Snips Multimeter Tone Probe and Tone Generator Butt Set Punchdown Tool • Hardware Tools – Cable Testers, TDRs, and OTDRs • Devices to test for broken cables – Cable testers » Continuity problems and wire map – TDRs time domain reflectometer » Locates copper cable breaks – OTDRs » Locates fiber-optic cable breaks Figure 15.1 Typical cable tester Figure 15.2 An EXFO AXS-100 OTDR (photo courtesy of EXFO) • Certifiers – Only use for slowdowns, not disconnects – Require a loopback on the far end – Ensure a cable can handle its rated capacity – Problems that reduce cable capacity • Cross talk • Attenuation • Interference • Voltage Event Recorder/Temperature Monitor – Detect power and heat problems – Cause intermittent problems – Heat problems in server rooms – Monitor power with voltage event recorder – Monitor temperature with temperature monitor • Protocol Analyzers – Monitor protocols at different layers • Application, Session, Network, Data Link – Both hardware and software tools • When to Use a Protocol Analyzer – You need to see data to analyze the problem • A session fails to start • A DNS server fails to respond • Confusing information appears on the network • You suspect a rogue DHCP server exists • Excess traffic is slowing down the network • Cable Stripper or Snip – Enable you to make UTP cables – Also need crimpers – Often combined in one tool Figure 15.3 A cable stripping and crimping tool • Multimeters – Test AC and DC voltage – Test resistance – Test Continuity – A great fallback when you do not have a cable tester • Tone Probes and Tone Generators – Work together to identify opposite ends of unlabeled cable runs – Tone generator puts a signal (tone) on wire – Tone probe on opposite end detects the signal • Butt Sets – Hand set – Use to tap into a 66- or 100-block to test a line • Punchdown Tools – Put UTP wires into 66- and 100-blocks – Repunch a connection to make sure contacts are set Figure 15.4 A punchdown tool in action • Software Tools – – – – – – – – – – – TRACERT/TRACEROUTE IPCONFIG/IFCONFIG PING and ARP PING NSLOOKUP/DIG HOSTNAME MTR ROUTE NBTSTAT NETSTAT Packet Sniffer Port Scanners • TRACERT/TRACEROUTE – Traces all routers between two points – Use to discover where a problem lies – Problem is just beyond the last router displayed before error – Some routers block TRACEROUTE packets – If TRACEROUTE is blocked, try PATHPING Tracing route to adsl-208-190-121-38.dsl.hstntx.swbell.net [208.190.121.38] over a maximum of 30 hops: 1 1 ms <1 ms 1 ms Router.totalhome [192.168.4.1] 2 38 ms 41 ms 70 ms adsl-208-190-12138.dsl.hstntx.swbell.net [208.190.121.38] Listing 15-1 Sample TRACEROUTE output • IPCONFIG/IFCONFIG – Displays IP settings – IPCONFIG without parameters • Basic information only – Ipconfig /all gives configuration details Ethernet adapter Main: Connection-specific DNS Suffix IPv6 Address . . . . . . . . . Temporary IPv6 Address . . . . Link-local IPv6 Address. . . . IPv4 Address . . . . . . . . . Subnet Mask . . . . . . . . . Default Gateway . . . . . . . . . . . . . . : : : : : : : 2001:470:bf88:1:fc2d:aeb2:99d2:e2b4 2001:470:bf88:1:5e4:c1ef:7b30:ddd6 fe80::fc2d:aeb2:99d2:e2b4%8 192.168.4.27 255.255.255.0 fe80::223:4ff:fe8c:b720%8 192.168.4.1 Tunnel adapter Local Area Connection* 6: Media State . . . . . . . . . . : Media disconnected Connection-specific DNS Suffix . : Listing 15-2 Sample IPCONFIG output eth0 Link encap:Ethernet HWaddr 00:02:b3:8a:7d:ae inet addr:192.168.4.19 Bcast:192.168.4.255 Mask:255.255.255.0 inet6 addr: 2001:470:bf88:1:202:b3ff:fe8a:7dae/64 Scope:Global inet6 addr: fe80::202:b3ff:fe8a:7dae/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:2206320 errors:0 dropped:0 overruns:0 frame:0 TX packets:925034 errors:0 dropped:0 overruns:0 carriers:0 collisions:0 txqueuelen:1000 RX bytes:292522698 (292.5 MB) TX bytes:132985596 (132.9 MB) lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:15414 errors:0 dropped:0 overruns:0 frame:0 TX packets:15414 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:1006671 (1.0 MB) TX bytes:1006671 (1.0 MB) Listing 15-3 Sample IFCONFIG output • PING – Queries by name or IP address – Uses ICMP packets – Works across routers – Problem: devices can block ICMP Pinging 192.168.4.19 with 32 bytes Reply from 192.168.4.19: bytes=32 Reply from 192.168.4.19: bytes=32 Reply from 192.168.4.19: bytes=32 Reply from 192.168.4.19: bytes=32 of data: time<1ms time<1ms time<1ms time<1ms TTL=64 TTL=64 TTL=64 TTL=64 Ping statistics for 192.168.4.19: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 0ms, Maximum = 0ms, Average = 0ms Listing 15-4 Sample PING output • ARP PING – Queries by IP address – Uses ARP packets – Problem: does not cross routers – Only on UNIX and UNIX-like systems ARPING 192.168.4.27 from 192.168.4.19 eth0 Unicast reply from 192.168.4.27 [00:1D:60:DD:92:C6] Unicast reply from 192.168.4.27 [00:1D:60:DD:92:C6] Unicast reply from 192.168.4.27 [00:1D:60:DD:92:C6] Unicast reply from 192.168.4.27 [00:1D:60:DD:92:C6] 0.875ms 0.897ms 0.924ms 0.977ms Listing 15-5 Sample ARPING output • NSLOOKUP/DIG – Both diagnose DNS problems – NSLOOKUP (all operating systems) • Poor tool – considered obsolete • Without switches, provides name and IP address of default DNS server – DIG – more powerful • Everyone but Windows dig mx totalsem.com Listing 15-6 The DIG command ; <<>> DIG 9.5.0-P2 <<>> mx totalsem.com ;; global options: printcmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 6070 ;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 1 ;; QUESTION SECTION: ;totalsem.com. IN MX ;; ANSWER SECTION: totalsem.com. 86400 IN MX 10 mx1c1.megamailservers.com. totalsem.com. 86400 IN MX 100 mx2c1.megamailservers.com. totalsem.com. 86400 IN MX 110 mx3c1.megamailservers.com. Listing 15-7 Output for the DIG command • HOSTNAME – Simplest of all utilities – Returns name of host from which it runs – HOSTNAME sample output c:\> c:\>hostname Mike-win7beta • My Traceroute (MTR) – Dynamic (keeps running) – Equivalent to TRACEROUTE – Not available in Windows My traceroute [v0.73] totaltest (0.0.0.0) Keys: Help Display mode Restart statistics Order of fields quit Packets Pings Host Loss% Snt Last Avg Best Wrst StDev 1. Router.totalhome 0.0% 5 0.8 0.8 0.7 0.9 0.1 2. adsl-208-190-121-38.dsl.hstntx.s 0.0% 4 85.7 90.7 69.5 119.2 20.8 Listing 15-9 Sample MTR output • ROUTE – Display and edit local routing table – Type route print =========================================================================== Interface List 8 ...00 1d 60 dd 92 c6 ...... Marvell 88E8056 PCI-E Ethernet Controller 1 ........................... Software Loopback Interface 1 =========================================================================== IPv4 Route Table =========================================================================== Active Routes: Network Destination Netmask Gateway Interface Metric 0.0.0.0 0.0.0.0 192.168.4.1 192.168.4.27 10 127.0.0.0 255.0.0.0 On-link 127.0.0.1 306 127.0.0.1 255.255.255.255 On-link 127.0.0.1 306 127.255.255.255 255.255.255.255 On-link 127.0.0.1 306 169.254.0.0 255.255.0.0 On-link 192.168.4.27 286 169.254.214.185 255.255.255.255 On-link 169.254.214.185 276 169.254.255.255 255.255.255.255 On-link 192.168.4.27 266 192.168.4.0 255.255.255.0 On-link 192.168.4.27 266 192.168.4.27 255.255.255.255 On-link 192.168.4.27 266 192.168.4.255 255.255.255.255 On-link 192.168.4.27 266 224.0.0.0 240.0.0.0 On-link 127.0.0.1 306 224.0.0.0 240.0.0.0 On-link 169.254.214.185 276 224.0.0.0 240.0.0.0 On-link 192.168.4.27 266 255.255.255.255 255.255.255.255 On-link 127.0.0.1 306 255.255.255.255 255.255.255.255 On-link 169.254.214.185 276 255.255.255.255 255.255.255.255 On-link 192.168.4.27 266 =========================================================================== Persistent Routes: None Listing 15-10 Sample ROUTE PRINT output • NBTSTAT – Windows only – Command-line equivalent of My Network Places – Must use a switch – nbtstat –n shows local NetBIOS names Main: Node IpAddress: [192.168.4.27] Scope Id: [] NetBIOS Local Name Table Name Type Status --------------------------------------------MIKESPC <00> UNIQUE Registered TOTALHOME <00> GROUP Registered MIKESPC <20> UNIQUE Registered TOTALHOME <1E> GROUP Registered Listing 15-11 Sample NBTSTAT output • NETSTAT – Shows current state of running IP processes – Shows what sessions are active – Provides statistics based on ports or protocols – Type netstat to show only current sessions – Type netstat –r to show routing table (like route print) Active Connections Proto Local Address TCP 127.0.0.1:27015 TCP 127.0.0.1:51090 TCP 127.0.0.1:52500 TCP 192.168.4.27:54731 TCP 192.168.4.27:55080 TCP 192.168.4.27:56126 TCP 192.168.4.27:62727 TCP 192.168.4.27:63325 TCP 192.168.4.27:63968 Foreign Address MikesPC:51090 MikesPC:27015 MikesPC:52501 72-165-61-141:27039 63-246-140-18:http acd4129913:https TOTALTEST:ssh 65.54.165.136:https 209.8.115.129:http State ESTABLISHED ESTABLISHED ESTABLISHED CLOSE_WAIT CLOSE_WAIT ESTABLISHED ESTABLISHED TIME_WAIT ESTABLISHED Listing 15-12 Sample NETSTAT output • Packet Sniffer – A.k.a. protocol analyzer or packet analyzer – Intercepts and logs network packets – Many choices – Software example: Wireshark – Dedicated hardware devices Figure 15.5 Wireshark in action • Port Scanners – Probes remotes system’s ports – Logs state of scanned ports – Good use: find unintentionally opened ports in order to close – Bad use: find open ports and use to break in – NMAP runs on UNIX – Angry IP Scanner for Windows Figure 15.6 Angry IP Scanner The Troubleshooting Process Memorize these problem analysis steps: 1. 2. 3. 4. 5. 6. 7. 8. 9. Information gathering—identify symptoms and problems Identify the affected areas of the network Establish if anything has changed Establish the most probable cause Determine if escalation is necessary Create an action plan and solution, identifying potential effects Implement and test the solution Identify the results and effects of the solution Document the solution and the entire process Troubleshooting Scenarios • Troubleshooting Scenario One – “I can’t log in!” • Biggest and most complex scenario • Log in from other machines • Attempt to log in yourself and try to PING • Use IPCONFIG or IFCONFIG • Troubleshooting Scenario Two – “I can’t get to this Web site!” • Have user try to reach another Web site • Try to ping the site by name and IP address • Determine whether DNS is functioning • Ping the gateway or proxy server • Ping other sites • If other sites reachable, notify problem site owner • If no sites available, notify your ISP • Troubleshooting Scenario Three – “Our Web server is sluggish!” • Connect from another location • If connection is also slow, problem with server • Check server logs for changes • Run Performance Monitor and compare new logs with previously established baseline logs • If connection from other location OK, run TRACERT command from user’s computer to reveal slow hop • Troubleshooting Scenario Four – “I can’t see anything on the network!” • Check connectivity • Ping a remote system • Ping loopback address – If error, run ipconfig /all and fix settings – If no error, check hardware » Run utility on NIC » Test cable • It’s Time to Escalate! – Broadcast storms – Switching loops – Route problems – Routing loops – Proxy ARP • Troubleshooting is fun! – Apply good troubleshooting methodology – Constantly increase your knowledge – Become a troubleshooting artist