{"id":2113,"date":"2019-07-19T00:23:07","date_gmt":"2019-07-19T00:23:07","guid":{"rendered":"http:\/\/wiki.thomasandsofia.com\/?p=2113"},"modified":"2020-05-13T10:43:53","modified_gmt":"2020-05-13T10:43:53","slug":"section-13-the-cisco-troubleshooting-methodology","status":"publish","type":"post","link":"https:\/\/wiki.thomasandsofia.com\/?p=2113","title":{"rendered":"Section 13: The Cisco Troubleshooting Methodology"},"content":{"rendered":"<p><a href=\"http:\/\/wiki.thomasandsofia.com\/?p=2082\">&lt; Section 12<\/a> | <a href=\"\/course-introduction\/\">Home<\/a> | <a href=\"\/section-14-cisco-router-and-switch-basics\/\">Section 14 &gt;<\/a><\/p>\n<p>35% Complete<\/p>\n<h1>71: The Cisco Troubleshooting Methodology\u00a0 &#8211; Introduction<\/h1>\n<p><a href=\"https:\/\/www.udemy.com\/cisco-icnd1\/learn\/lecture\/8605212#overview\" target=\"_blank\" rel=\"noopener\">https:\/\/www.udemy.com\/cisco-icnd1\/learn\/lecture\/8605212#overview<\/a><\/p>\n<h1>72: The Cisco Troubleshooting Methodology<\/h1>\n<p><a href=\"https:\/\/www.udemy.com\/cisco-icnd1\/learn\/lecture\/8605222#overview\" target=\"_blank\" rel=\"noopener\">https:\/\/www.udemy.com\/cisco-icnd1\/learn\/lecture\/8605222#overview<\/a><\/p>\n<p><a href=\"http:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/ctsm1.png\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-2118\" src=\"http:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/ctsm1.png\" alt=\"\" width=\"381\" height=\"327\" srcset=\"https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/ctsm1.png 381w, https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/ctsm1-300x257.png 300w, https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/ctsm1-150x129.png 150w\" sizes=\"auto, (max-width: 381px) 100vw, 381px\" \/><\/a><\/p>\n<ul>\n<li>Define the Problem<\/li>\n<li>Gather Information<\/li>\n<li>Analyze Information<\/li>\n<li>Eliminate Potential Causes<\/li>\n<li>Propose Hypothesis<\/li>\n<li>Test Hypothesis<\/li>\n<li>Solve Problem and Document Solution<\/li>\n<\/ul>\n<h2>Troubleshooting Methods<\/h2>\n<p><a href=\"http:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/ctsm2.png\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-2119\" src=\"http:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/ctsm2.png\" alt=\"\" width=\"683\" height=\"254\" srcset=\"https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/ctsm2.png 683w, https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/ctsm2-300x112.png 300w, https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/ctsm2-150x56.png 150w\" sizes=\"auto, (max-width: 683px) 100vw, 683px\" \/><\/a><\/p>\n<ul>\n<li>Top Down\n<ul>\n<li>Start at Layer 7 and work your way down to Layer 1<\/li>\n<\/ul>\n<\/li>\n<li>Bottom Up\n<ul>\n<li>Start at Layer 1 and work your way up to Layer 7<\/li>\n<\/ul>\n<\/li>\n<li>Divide and Conquer\n<ul>\n<li>Go straight to the most obvious layer and work your way either up or down.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<h2>Troubleshooting methods<\/h2>\n<ul>\n<li>Compare configurations<\/li>\n<li>Trace the path\n<ul>\n<li>Very common<\/li>\n<li>Start at the source and work your way to the destination<\/li>\n<\/ul>\n<\/li>\n<li>Swap out components<\/li>\n<\/ul>\n<h2>Common Commands<\/h2>\n<ul>\n<li>Ping\n<ul>\n<li>Uses ICMP<\/li>\n<li>Verifies 2-way connectivity<\/li>\n<li>Source sends a PING request<\/li>\n<li>Destination sends a PING reply<\/li>\n<\/ul>\n<\/li>\n<li>Traceroute\n<ul>\n<li>Similar to PING but measures hop by hop based on a &#8216;TTL&#8217; type value<\/li>\n<li>Each TTL is a hop.\u00a0 First one hop, then two, then 3&#8230;<\/li>\n<li>This way you can tell if something breaks in between<\/li>\n<li>Many routers are configured NOT to return PING replies, so you may not get values &#8216;mid stream&#8217; but will get values farther down the path<\/li>\n<\/ul>\n<\/li>\n<li>Telnet\n<ul>\n<li>Generally used to access command line on a device\n<ul>\n<li>Very similar to SSH, but insecure.\u00a0 All data is sent clear text.<\/li>\n<\/ul>\n<\/li>\n<li>Telnet can be used to check specific ports.\u00a0 Default is 23, but can be easily set to something else to see if:\n<ul>\n<li>A port is open (not blocked by a firewall)<\/li>\n<li>A service is &#8216;listening&#8217; on a specific host, such as:\n<ul>\n<li>53 for DNS<\/li>\n<li>80 for HTTP<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<h1>73: Cisco Troubleshooting Methodology &#8211; Lab<\/h1>\n<p><a href=\"https:\/\/www.udemy.com\/cisco-icnd1\/learn\/lecture\/8605228#overview\" target=\"_blank\" rel=\"noopener\">https:\/\/www.udemy.com\/cisco-icnd1\/learn\/lecture\/8605228#overview<\/a><\/p>\n<p><a href=\"http:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/tbrl1.png\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-2121\" src=\"http:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/tbrl1.png\" alt=\"\" width=\"448\" height=\"418\" srcset=\"https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/tbrl1.png 448w, https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/tbrl1-300x280.png 300w, https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/tbrl1-150x140.png 150w\" sizes=\"auto, (max-width: 448px) 100vw, 448px\" \/><\/a><\/p>\n<h2>The Issue<\/h2>\n<ul>\n<li>User on PC behind R1 claims DNS isn&#8217;t working<\/li>\n<li>DNS is hosted on R3<\/li>\n<\/ul>\n<h2>Troubleshooting<\/h2>\n<h4>Ping R3 from R1 using the hostname<\/h4>\n<pre>R1#ping R3\r\nTranslating \"R3\"...domain server (10.10.30.1)\r\n% Unrecognized host or address, or protocol not running<\/pre>\n<p>DNS not working confirmed.<\/p>\n<h3>Ping the IP to see if connectivity exists<\/h3>\n<pre>R1#ping 10.10.30.1\r\nType escape sequence to abort.\r\nSending 5, 100-byte ICMP Echos to 10.10.30.1, timeout is 2 seconds:\r\n.....\r\nSuccess rate is 0 percent (0\/5)<\/pre>\n<p>Cannot access DNS router confirmed.<\/p>\n<h4>Run a traceroute to see where the breakdown occurs<\/h4>\n<pre>R1#traceroute 10.10.30.1\r\nType escape sequence to abort.\r\nTracing the route to 10.10.30.1\r\nVRF info: (vrf in name\/id out name\/id)\r\n  1 10.10.10.2 4 msec 4 msec 0 msec\r\n  2 *  in  *<\/pre>\n<p>R2 is OK, but no response from R3.<\/p>\n<h4>Check if R2 can ping R3<\/h4>\n<pre>R2#ping 10.10.30.1\r\nType escape sequence to abort.\r\nSending 5, 100-byte ICMP Echos to 10.10.30.1, timeout is 2 seconds:\r\n.....\r\nSuccess rate is 0 percent (0\/5)<\/pre>\n<p>R2 cannot access R3 confirmed.<\/p>\n<h4>Check if there is a route set from R2 to 10.10.30.1<\/h4>\n<pre>R2#show route\r\n.. lots of stuff, but no route to 10.10.30.1 ...<\/pre>\n<p>Route does not exist.<\/p>\n<h4>Fix the route<\/h4>\n<pre>R2(config)#ip route 10.10.30.0 255.255.255.0 10.10.20.1<\/pre>\n<h4>Try Ping gain<\/h4>\n<pre>R2#ping 10.10.30.1\r\nType escape sequence to abort.\r\nSending 5, 100-byte ICMP Echos to 10.10.30.1, timeout is 2 seconds:\r\n!!!!!\r\nSuccess rate is 100 percent (5\/5), round trip min\/avg\/max = 1\/3\/0 ms<\/pre>\n<p>Ping re-established<\/p>\n<h3>Verify the issue has been corrected<\/h3>\n<h4>Attempt Ping from R1 to R3 again<\/h4>\n<pre>R1#ping 10.10.30.1\r\nType escape sequence to abort.\r\nSending 5, 100-byte ICMP Echos to 10.10.30.1, timeout is 2 seconds:\r\n!!!!!\r\nSuccess rate is 100 percent (5\/5), round trip min\/avg\/max = 1\/1\/4 ms<\/pre>\n<p>Full connection exists between R1 and R3.<\/p>\n<h4>Check if DNS is working now<\/h4>\n<pre>R1#ping R3\r\nTranslating \"R3\"...domain server (10.10.30.1)\r\n% Unrecognized host or address, or protocol not running<\/pre>\n<p>DNS still not working.<\/p>\n<h4>Check if DNS is running on the router<\/h4>\n<pre>R1#telnet 10.10.30.1 53\r\n% Connection refused by remote host<\/pre>\n<p>DNS Not running on R3 confirmed.<\/p>\n<h4>Enable DNS Services on R3<\/h4>\n<pre>R3(config)#ip dns server\r\nR3(config)#exit\r\nR3(config)#do telnet 10.10.30.1 53\r\nTrying 10.10.30.1, 53 ... Open\r\n\r\n[Connection to 10.10.30.1 closed by foregn host]<\/pre>\n<p>DNS Service has been re-enabled<\/p>\n<h4>Confirm DNS is working on R1<\/h4>\n<pre>R1#ping R3\r\nType escape sequence to abort.\r\nSending 5, 100-byte ICMP Echos to 10.10.30.1, timeout is 2 seconds:\r\n!!!!!\r\nSuccess rate is 100 percent (5\/5), round trip min\/avg\/max = 1\/2\/4 ms<\/pre>\n<h3>Problem Solved!<\/h3>\n<h1>74: The Cisco Troubleshooting Methodology &#8211; Lab Exercises<\/h1>\n<p><a href=\"https:\/\/www.udemy.com\/cisco-icnd1\/learn\/lecture\/8605232#content\" target=\"_blank\" rel=\"noopener\">https:\/\/www.udemy.com\/cisco-icnd1\/learn\/lecture\/8605232#content<\/a><\/p>\n<p><a href=\"http:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/13-The-Cisco-Troubleshooting-Methodology.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-2122\" src=\"http:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/13-The-Cisco-Troubleshooting-Methodology.jpg\" alt=\"\" width=\"863\" height=\"397\" srcset=\"https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/13-The-Cisco-Troubleshooting-Methodology.jpg 863w, https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/13-The-Cisco-Troubleshooting-Methodology-300x138.jpg 300w, https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/13-The-Cisco-Troubleshooting-Methodology-768x353.jpg 768w, https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/13-The-Cisco-Troubleshooting-Methodology-150x69.jpg 150w\" sizes=\"auto, (max-width: 863px) 100vw, 863px\" \/><\/a><\/p>\n<p><a href=\"http:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/13-The-Cisco-Troubleshooting-Methodology-Lab-Exercise.pdf\">13 The Cisco Troubleshooting Methodology Lab Exercise<\/a><\/p>\n<p><a href=\"http:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2019\/07\/13-The-Cisco-Troubleshooting-Methodology-Answer-Key.pdf\">13 The Cisco Troubleshooting Methodology Answer Key<\/a><\/p>\n<p>There are at least 3 errors!<\/p>\n","protected":false},"excerpt":{"rendered":"<p>&lt; Section 12 | Home | Section 14 &gt; 35% Complete 71: The Cisco Troubleshooting Methodology\u00a0 &#8211; Introduction https:\/\/www.udemy.com\/cisco-icnd1\/learn\/lecture\/8605212#overview 72: The Cisco Troubleshooting Methodology https:\/\/www.udemy.com\/cisco-icnd1\/learn\/lecture\/8605222#overview Define the Problem Gather Information Analyze Information Eliminate Potential Causes Propose Hypothesis Test Hypothesis Solve Problem and Document Solution Troubleshooting Methods Top Down Start at Layer 7 and work your ..<\/p>\n<div class=\"clear-fix\"><\/div>\n<p><a href=\"https:\/\/wiki.thomasandsofia.com\/?p=2113\" title=\"read more...\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[45],"tags":[],"class_list":["post-2113","post","type-post","status-publish","format-standard","hentry","category-icnd1-ccent"],"_links":{"self":[{"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/posts\/2113","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2113"}],"version-history":[{"count":7,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/posts\/2113\/revisions"}],"predecessor-version":[{"id":2881,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/posts\/2113\/revisions\/2881"}],"wp:attachment":[{"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2113"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2113"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2113"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}