Ubuntu: why command telnet responds strange? [closed]



Question:

i pass network course university 4 years before,i have a question that is possible amateur ,please help me.. i have ubuntu on vmware.i use this command:

telnet google.com 80  

it responds:

Trying 74.125.195.139... Connected to google.com. Escape character is '^]'.

then i type ls command: it returns!

HTTP/1.0 400 Bad Request  Content-Type: text/html; charset=UTF-8  Content-Length: 1555  Date: Wed, 27 Jan 2016 12:53:29 GMT  Server: GFE/2.0    <!DOCTYPE html>  <html lang=en>    <meta charset=utf-8>    <meta name=viewport content="initial-scale=1, minimum-scale=1, width=device-width">    <title>Error 400 (Bad Request)!!1</title>    <style>      *{margin:0;padding:0}html,code{font:15px/22px arial,sans-serif}html{background:#fff;color:#222;padding:15px}body{margin:7% auto 0;max-width:390px;min-height:180px;padding:30px 0 15px}* > body{background:url(//www.google.com/images/errors/robot.png) 100% 5px no-repeat;padding-right:205px}p{margin:11px 0 22px;overflow:hidden}ins{color:#777;text-decoration:none}a img{border:0}@media screen and (max-width:772px){body{background:none;margin-top:0;max-width:none;padding-right:0}}#logo{background:url(//www.google.com/images/branding/googlelogo/1x/googlelogo_color_150x54dp.png) no-repeat;margin-left:-5px}@media only screen and (min-resolution:192dpi){#logo{background:url(//www.google.com/images/branding/googlelogo/2x/googlelogo_color_150x54dp.png) no-repeat 0% 0%/100% 100%;-moz-border-image:url(//www.google.com/images/branding/googlelogo/2x/googlelogo_color_150x54dp.png) 0}}@media only screen and (-webkit-min-device-pixel-ratio:2){#logo{background:url(//www.google.com/images/branding/googlelogo/2x/googlelogo_color_150x54dp.png) no-repeat;-webkit-background-size:100% 100%}}#logo{display:inline-block;height:54px;width:150px}    </style>    <a href=//www.google.com/><span id=logo aria-label=Google></span></a>    <p><b>400.</b> <ins>That’s an error.</ins>    <p>Your client has issued a malformed or illegal request.  <ins>That’s all we know.</ins>  Connection closed by foreign host.  
  • my question is in telnet protocol,we have HTTP???

thanks for reply.


Solution:1

This is a perfectly reasonable response, if you connect to a web server.

Telnet is, besides other things, just a plaintext conversation between two computers. It's super basic. So if you connect to Google on port 80, you're going to talk directly to the web server, in a similar way to how the browser would.

You see an error because ls is not a valid HTTP request. GET / is valid and works.

Similar will be true of any other plaintext protocols. If you want a shell server over telnet, you need to connect to one. They still exist but you really aught to be using SSH these days. It's better in almost every measurable way.

Why did Telnet ever exist? To serve as a remote terminal... But you're talking as if Telnet only came into existence last month. It's 47 years old. Many things that used to be useful have been replaced with modern equivalents.


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