{"id":696,"date":"2010-04-15T20:30:58","date_gmt":"2010-04-15T19:30:58","guid":{"rendered":"http:\/\/mccltd.net\/blog\/?p=696"},"modified":"2010-04-15T20:30:58","modified_gmt":"2010-04-15T19:30:58","slug":"tcp-and-udp-small-servers","status":"publish","type":"post","link":"http:\/\/darenmatthews.com\/blog\/?p=696","title":{"rendered":"TCP and UDP Small Servers"},"content":{"rendered":"<p>TCP and UDP small servers are servers (daemons, in Unix parlance)  that \t run in the router which are useful for diagnostics.<span> <!--more--><\/span><\/p>\n<h3><a name=\"tcp\">TCP Small Servers<\/a><\/h3>\n<p>The TCP small servers are:<\/p>\n<ul>\n<li><strong>Echo:<\/strong> Echoes back whatever you type through the \t\t<strong>telnet x.x.x.x echo<\/strong> command.<\/li>\n<li><strong>Chargen:<\/strong> Generates a stream of ASCII data. Use the \t\t<strong>telnet x.x.x.x chargen<\/strong> command.<\/li>\n<li><strong>Discard:<\/strong> Throws away whatever you type. Use the \t\t<strong>telnet x.x.x.x discard<\/strong> command.<\/li>\n<li><strong>Daytime:<\/strong> Returns system date and time, if it is \t\tcorrect. It is correct if you run Network Time Protocol (NTP), or have  set the \t\tdate and time manually from the exec level. Use the <strong>telnet x.x.x.x \t\tdaytime<\/strong> command.<\/li>\n<\/ul>\n<p>Replace x.x.x.x with the IP address of your router. Most routers  inside \t Cisco run the small servers.<\/p>\n<h3><a name=\"udp_servers\">UDP Small Servers<\/a><\/h3>\n<p>The UDP small servers are:<\/p>\n<ul>\n<li><strong>Echo:<\/strong> Echoes the payload of the datagram you send.<\/li>\n<li><strong>Discard: <\/strong>Silently pitches the datagram you send.<\/li>\n<li><strong>Chargen:<\/strong> Pitches the datagram you send, and responds \t\twith a 72-character string of ASCII characters terminated with a  CR+LF.<\/li>\n<\/ul>\n<p><strong>Notes:<\/strong><\/p>\n<ul>\n<li>Almost all Unix boxes support the small servers listed above.<\/li>\n<li>The router also offers finger service and async line bootp service, \t\twhich you can independently turn off with the configuration global  commands \t\t<strong>no service finger<\/strong> and <strong>no ip bootp \t\tserver<\/strong>, respectively.<\/li>\n<\/ul>\n<h2><a name=\"commands\">TCP and UDP Commands<\/a><\/h2>\n<p>The commands to enable for the TCP and UDP small servers are \t <strong>service tcp-small-servers<\/strong> and <strong>service \t udp-small-servers<\/strong>.<\/p>\n<p>The TCP and UDP small servers are enabled by default on Cisco IOS \t Software Version 11.2 and earlier. They may be disabled using the  commands \t <strong>no service tcp-small-servers<\/strong> and <strong>no \t service udp-small-servers<\/strong>. They are disabled by default on Cisco \t IOS Software Versions 11.3 and later.<\/p>\n<p>It is recommended that you do not enable these services unless it  is \t absolutely necessary. These services could be exploited indirectly to  gain \t information about the target system or directly as is the case with  the fraggle \t attack which uses UDP echo.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>TCP and UDP small servers are servers (daemons, in Unix parlance) that run in the router which are useful for diagnostics.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[13],"tags":[34,24],"_links":{"self":[{"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/696"}],"collection":[{"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=696"}],"version-history":[{"count":1,"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/696\/revisions"}],"predecessor-version":[{"id":697,"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/696\/revisions\/697"}],"wp:attachment":[{"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=696"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=696"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=696"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}