{"id":12824,"date":"2021-03-07T20:25:25","date_gmt":"2021-03-07T20:25:25","guid":{"rendered":"https:\/\/linuxiac.com\/?p=12824"},"modified":"2022-03-15T15:46:48","modified_gmt":"2022-03-15T15:46:48","slug":"telnet-to-port","status":"publish","type":"post","link":"https:\/\/linuxiac.com\/telnet-to-port\/","title":{"rendered":"Telnet to a Port to Test Network Connectivity"},"content":{"rendered":"\n<p>Telnet is a client-server protocol. Network and system administrators use it to configure and administer network devices such as servers, routers, etc. But all information exchanged in a telnet session between a client and server is unencrypted. Currently, this application has been replaced by <a href=\"https:\/\/linuxiac.com\/how-to-use-ssh-tunneling\/\">SSH<\/a>, which provides the same type of service, but is encrypted.<\/p>\n\n\n\n<p>Nowadays telnet is widely used <a href=\"https:\/\/linuxiac.com\/how-to-check-for-open-ports-in-linux-with-netstat-lsof-and-nmap\/\">to verify connectivity to services<\/a> that are based on TCP protocol. Many people find the challenge of checking if a port is opened to be confusing sometimes. One of the most efficient ways is to use the <a href=\"https:\/\/linuxiac.com\/wireshark-3-6-0\/\">network protocol<\/a> Telnet.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-using-telnet-to-test-open-ports\">Using Telnet to Test Open Ports<\/h2>\n\n\n\n<p>Though most users opt to work with graphical interfaces, Telnet is one of the simplest ways to check connectivity on certain ports. Let&#8217;s see how we can use the <code>telnet<\/code> command to test the TCP port connectivity. The syntax to use it is as follows:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"CSS\" data-shcb-language-slug=\"css\"><span><code lang=\"bash\" class=\"hljs language-css language-bash\"><span class=\"hljs-selector-tag\">telnet<\/span> <span class=\"hljs-selector-attr\">&#91;hostname\/IP address]<\/span> <span class=\"hljs-selector-attr\">&#91;port number]<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">CSS<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">css<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p>Put the IP address or domain name of the server you\u2019re trying to connect to in place of [hostname\/IP address] and replace the second brackets [port number] with the port number connection to which you want to test.<\/p>\n\n\n\n<p>As a result of the execution of the command can be:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>&#8220;<strong>Network is unreachable<\/strong>&#8221; if the port is closed or blocked by the firewall.<\/li>\n\n\n\n<li>&#8220;<strong>Connection refused<\/strong>&#8221; if the service is down\/not listening on the specified port, but the port is reachable.<\/li>\n\n\n\n<li>&#8220;<strong>Connected to server_ip<\/strong>&#8221; if the connection is successful.<\/li>\n<\/ul>\n\n\n\n<p>For example, to telnet to a port <code>80<\/code> on <code>192.168.0.1<\/code> to verify connection, issue the command:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"CSS\" data-shcb-language-slug=\"css\"><span><code lang=\"bash\" class=\"hljs language-css language-bash\"><span class=\"hljs-selector-tag\">telnet<\/span> 192<span class=\"hljs-selector-class\">.168<\/span><span class=\"hljs-selector-class\">.0<\/span><span class=\"hljs-selector-class\">.1<\/span> 80<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">CSS<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">css<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p>If the connection succeeds the result of executing the command would look like this:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code lang=\"xml\" class=\"hljs language-javascript language-xml\">Trying <span class=\"hljs-number\">192.168<\/span><span class=\"hljs-number\">.0<\/span><span class=\"hljs-number\">.1<\/span>...\nConnected to <span class=\"hljs-number\">192.168<\/span><span class=\"hljs-number\">.0<\/span><span class=\"hljs-number\">.1<\/span>.\nEscape character is <span class=\"hljs-string\">'^]'<\/span>.<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p>Example of unsuccessful connection:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"HTML, XML\" data-shcb-language-slug=\"xml\"><span><code lang=\"xml\" class=\"hljs language-xml language-xml\">Trying 192.168.0.1...\ntelnet: Unable to <span class=\"hljs-tag\">&lt;<span class=\"hljs-name\">a<\/span> <span class=\"hljs-attr\">href<\/span>=<span class=\"hljs-string\">\"https:\/\/linuxiac.com\/ubuntu-remote-desktop\/\"<\/span>&gt;<\/span>connect to remote host<span class=\"hljs-tag\">&lt;\/<span class=\"hljs-name\">a<\/span>&gt;<\/span>: Network is unreachable<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">HTML, XML<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">xml<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>or<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-5\" data-shcb-language-name=\"CSS\" data-shcb-language-slug=\"css\"><span><code lang=\"xml\" class=\"hljs language-css language-xml\"><span class=\"hljs-selector-tag\">Trying<\/span> 192<span class=\"hljs-selector-class\">.168<\/span><span class=\"hljs-selector-class\">.0<\/span><span class=\"hljs-selector-class\">.1<\/span>...\n<span class=\"hljs-selector-tag\">telnet<\/span>: <span class=\"hljs-selector-tag\">Unable<\/span> <span class=\"hljs-selector-tag\">to<\/span> <span class=\"hljs-selector-tag\">connect<\/span> <span class=\"hljs-selector-tag\">to<\/span> <span class=\"hljs-selector-tag\">remote<\/span> <span class=\"hljs-selector-tag\">host<\/span>: <span class=\"hljs-selector-tag\">Connection<\/span> <span class=\"hljs-selector-tag\">refused<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-5\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">CSS<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">css<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<div style=\"height:20px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p>Of course, with the <code>telnet<\/code> command, you can test not only remote but also localhost services. Just replace the <em>[hostname\/IP address]<\/em> part with <code>localhost<\/code> or <code>127.0.0.1<\/code>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Conclusion<\/h2>\n\n\n\n<p>We hope this article was beneficial in learning about how to <code>telnet<\/code> to a port to check whether a port is open or not. For more about&nbsp;the <code>telnet<\/code>&nbsp;command in Linux, consult its&nbsp;<a href=\"https:\/\/linux.die.net\/man\/1\/telnet\" target=\"_blank\" rel=\"noreferrer noopener\">manual page<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Telnet is one of the simplest ways to check port connectivity. Learn how to telnet to a port to check whether a port is open or not.<\/p>\n","protected":false},"author":10,"featured_media":26308,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8,4417],"tags":[1484,3694,3170],"class_list":["post-12824","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-tips","category-linux-knowledge","tag-commands","tag-networking","tag-telnet"],"blocksy_meta":{"styles_descriptor":{"styles":{"desktop":"","tablet":"","mobile":""},"google_fonts":[],"version":6},"post_title_panel":"","has_hero_section":"default","9491615ac614b7e157b01626a3177549":"","hero_section":"type-2","hero_elements":[{"id":"custom_title","enabled":true,"heading_tag":"h1","title":"Home","__id":"i3T_SVPCv4six2Y0Bucwj"},{"id":"custom_description","enabled":false,"description_visibility":{"desktop":true,"tablet":true,"mobile":false},"__id":"iDURqQUcIVPXoIGnnQhJ-"},{"id":"custom_meta","enabled":true,"meta_elements":[{"id":"author","enabled":true,"label":"By","has_author_avatar":"yes","avatar_size":50,"__id":"nqzwhWyI96ZDua29RLO7y"},{"id":"post_date","enabled":false,"label":"On","date_format_source":"default","date_format":"M 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