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Understanding Network Failures

Understanding Network Failures. 2.1 "ping usage”. Please enable audio (speakers, volume) & full-screen <F11>. Click to continue. 2.1. Understanding Network Failures. Click to continue. 1.0 Understanding Network Failures (program overview)

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Understanding Network Failures

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  1. Understanding Network Failures 2.1 "ping usage” Please enable audio (speakers, volume) & full-screen <F11> Click to continue. . . 2.1

  2. Understanding Network Failures Click to continue. . . 1.0 Understanding Network Failures (program overview) 2.0 Intro to ping2.1 Usage Intro (Strybd prototype) 2.2 Lab 2.3 Assessment • Plus addt’l e-Learning Modules, labs and assessments: • 3.0 Intro to traceroute, lab, assessment • 4.0 Intro to netstat, lab, assessment • 5.0 Intro to ipconfig (ifconfig), lab, assessment • 6.0 Intro to nslookup, lab, assessment • 7.0 Intro to whois, lab, assessment • 8.0 Pre-Assessment Modules (pre-tests for each module) • 9.0 Assessment Modules • 10.0 Labs: User Tools & Network Utilities (telnet short-cuts, PCHAR/TTCP,…?)

  3. 2.1 Lesson Objectives Click to continue. . . In this lesson, students will utilize “ping” to validate network connections, and analyze responses reported from “ping” • Audience information: • Call Center I & II/CCNA I & II • 20 Minutes (duration) 2.1.1

  4. ? Network failures: The sky is falling! 2 1 Server 1 Click to continue. . . Customer Support: “How may I help you?” The Internet e0 Click to continue. . . s2 User: “My Internet is down!” Center s0 s1 s0 s0 CS: “Can you describe Boaz Eva e0 e0 the problem for me?" User: “Becky isn't getting my text messages!: (demo) Click to run demo. . . 3 4 5 6 Recent policy change: No "text" Recent policy change: No "text" “Becky” Becky 2.1.2 Click to continue. . .

  5. Before escalating this call . . . • ? Policy change or local failure? • Do the interfaces show a link light? • LAN/WAN connectivity? (# ping yahoo.com) For most users: The browser is “The Internet” Example: Text messages are being dropped by “Boaz” router • . . . the sky isn’t falling! 2.1.3

  6. Review: Before escalating a customer call . . . The browser is “The Internet” (for most users) Consider local failures first! • Does the interface show a link light? Identify recent (local) modifications • Are new patches applied? Applied correctly?

  7. Experience suggests . . . Many local network “failures” are due to operator error • Un-skilled users, un-trained personnel, invalid configurations . . . Suspect recent changes or modifications • Have all required patches been applied correctly? • Check the logs (recent activity? upgrades?)

  8. 1.0 (Review): Common Causes of Network Failures Alert: s2is “down”! Circuit “outages” are a common cause of real (actual) network faults • Example: Heavy equipment workers & sea dredging have cut cabling, power lines, deep sea fibre (very rare!) • Example: Denial of Service (DoS): More common. . .? Click the "heavy equipment worker". . . • DoS Attacks = Sluggish network segments • For our example, the Internet is down! • Example: “ping” may be used to verify all subnets “up” during DoS attack Click to validate networks (demo) • Status: (ping or traceroute script) • All Routers and sub-nets “up” (reachable), except . . • Center-s2 (Serial_2) “unreachable” during attack 2.1.4 (1.0)

  9. 2 Boaz WS4 192.168.10.62 # ping 192.16.10.62 Server 1 Round-trip: A Request/Reply “pair” Sw1-8 Center-sw1 Echo Request: “Is WS4 online?” (demo) e0 s2 Click to continue. . . Echo Reply: Center “Request received!” (demo) s0 s1 s0 Click to continue. . . s0 Eva e0 e0 What if this ping fails? Reduce scope of test. . . How many intervening devices, as shown? Boaz-sw1 Sw1-2 3 5 6 2.1.5 Click to continue. . .

  10. 2 Center Example: Using ping Server 1 Initial troubleshooting # ping <IP-address> (e.g. ping<local nodes>) e0 s2 Demonstration:“ping Serial_0” Serial_0 Serial_0 Serial_0 s1 s0 s0 # ping 192.168.10.65 Boaz Eva e0 e0 Type <ESC> to abort. Sending 5, 100-byte ICMP Echosto 192.168.10.65, timeout is 2 seconds: ! ! ! ! ! Success rate is100 percent (5/5), round-trip Min/Avg/Max = 4/6/9 ms 3 4 5 6 Click to continue. . . 2.1.6 Click to continue. . .

  11. Initial Network Tests “My internet is down” could be a sluggish network segment, slow server, or equipment fault . . . ? • How many intervening devices? (firewall, appliance, proxy server, CSU/DSU, …) • Is it a recurring fault or temporary slowness or random outages? Collecting accurate failure data is crucial!

  12. Review: Initial Network Tests: What to consider? User: “My internet is down . . .” • Could be an intervening application server, device or appliance • Intermittent faults may appear as temporary service outages (e.g. threshold exceeded, server rebooting, . . .) “ping yahoo.com” = “Are you there?”

  13. ping: Validate Connectivity Standard diagnostics using “ping”: • # ping 127.0.0.1 • # ping <IP address of local host> • # ping <default-gateway IP address> • # ping <remote destination IP address> • # ping <remote hostname>

  14. What is a 20% success rate? ECHO Request (from WS2): Are you "online", WS4? # ping 192.168.10.62 Type <ESC> to abort. Sending 5, 100-byte ICMP Echoes to 192.168.10.62 ECHO Request (from WS2): 5 Request/Reply "pairs" 100-byte, ICMP packets timeout is 2 seconds: . . . . ! (.) period after 2 sec. Success rate is 20 percent (1/5), round-trip _min/avg/max = 76/76/76 ms ECHO Reply (to WS2): 1 of 5 = 20% success Temporary? Recurring? ping responses:(.) = timeout, (!) = success, (N) = Net-Unreachable, (U) = Dest-Unreachable 2.1.7

  15. Review: Using ping “ping 192.168.10.65” will validate network connectivity (between source and destination) • “Are you there?” (ECHO Request sent from source) • “I am connected” (ECHO Reply received from destination) • 5 of 5 packets = 100% success rate See, also, www.cwdotson.com/NetFailures,dd2

  16. Questions: Using ping Recall the ping responses: An exclamation (!) indicates which test result? A) Failure; B) Success; C) Time out B) Success Recall the ping responses, a period (.) indicates: A) Failure; B) Success; C) Time out C) Timeout False (True/False) Ping is an excellent performance monitor (True/False) 2 of 5 successful packets indicates a success rate of 20% False (40% success) (True/False) When ping is executed, the source issues an Echo Request to the destination. True 2.1.8

  17. Using “ping” continued. . . ping uses ICMP Echo Request/Reply • ICMP Message types: • EchoRequest/EchoReply: “ping” connectivity • Dest unreachable: Packet delivery problem • Time exceeded: Packet discarded (TTL) • Redirect: Better route via “router_ip_address” There are many ways to utilize “ping” . . .

  18. Extended “ping” (options) • Specify data length, source and dest. addresses • Specify “next hop” • Set timeout interval (default: 2 seconds) • Specify ping count (repeated ping attempts) • Specify data pattern (sliding “1s”, or 0xABCD) • Validate response data (data validity) • Set: Don’t Fragment, include Timestamp, etc

  19. Intermittent Vs. Recurring Failures Intermittent faults: Difficult to identify & fix • Occasional errors (“Time exceeded”) • Errors may occur only under certain conditions (e.g. temporary outages, threshold exceeded) Recurring faults: Easier to identify (Server, router, or interface is “down”) • Chronic fault (“Network unreachable”)

  20. Limitations of “ping” ping can validate “connectivity”only! # ping yahoo.com Type <ESC> to abort. Sending 5, 100-byte ICMP Echos to 209.131.36.159 timeout is 2 seconds: ! ! ! ! ! • “100%” success expected! • ICMP packets do NOT represent “real world” traffic Success rate is 100 percent (5/5), round-trip _min/avg/max = 23/26/29 ms • ping: Response is for few, small pkts • Caution:pingis a poor tool for performance monitoring! • Network performance varies for ”real world” traffic • Text traffic is much different than streaming video or VoIP

  21. Review: ping limitations ping: Validates network paths • Sends a few, small packets (e.g. 100-byte, ICMP packets are not “real world” traffic) • For small, idle networks 100% success rates are common (not “real world”) Only confirms basic connectivity between remote nodes

  22. Destination Unreachable Hosts/Routers return “Dest. Unreachable” when: • Data cannot be completely delivered to receiving application at the destination host • Example: ICMP messages sent back to WS2 is reponse to “ping” (e.g. # ping serial_0) • Network unreachable: No matching route • Host unreachable: packet is routable but host not responding • Can’t fragment: Older router/Large pkts (must fragmnt but “do not frag” bit set) • Protocol unreachable: Transport layer protocol “down” at host • Port unreachable: Host application fault (port un-opened by app)

  23. Isolating IP Routing Problems: Use ping to trace a path (identify “last” router) • telnet to last “traced” router or node • # telnet <IP address-router_lastknown>

  24. Lesson Summary In this lesson we: • Examined LAN/WAN failures (DoS, circuit breaks) • Used “ping” to validate a network connection with remote nodes • Examined responses reported by “ping” to analyze network performance 2.1.9 The End. . . The End. . .

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