Changing the underscore '_' to a hyphen '-' also seems to work.

Hello from route 1 (/r1), 
resultFromroute = http://myapp-v2f.net/r1 = route('namedroute1')
resultFromLinkOnResultFromRoute = <a href="http://myapp-v2f.net/r1">http://myapp-v2f.net/r1</a> = HTML::link(resultFromroute,resultFromroute)

Hi lookitsatravis

thanks for the response, and interesting with the valid hostname.

I have just changed the hostname to something valid and thats all good...

anyway: I don't think that the headers are weird, mostly because, I wouldn't expect apache to serve the correct page if that was the case...

this is the response from php's getallheaders

Headers:
text/html, application/xhtml+xml, */*
da
Mozilla/5.0 (Windows NT 6.3; WOW64; Trident/7.0; rv:11.0) like Gecko
gzip, deflate
myapp_v2f.net
1
Keep-Alive

I have printed the output using a small unittest , that I guess 'might' not be infuenced by headers et al.

public function testHTMLLinkWhitUnderscoreInAppUrl()
{
  echo "\r\n" . 'HTML::link(\'/r1\')'."\r\n\t".HTML::link('/r1');
  echo "\r\n" . 'route(\'namedroute\'):'."\r\n\t".route('namedroute');
  echo "\r\n" . 'HTML::link(route(\'namedroute\')):'."\r\n\t". HTML::link(route('namedroute'));
}

output:

HTML::link('/r1')
    <a href="http://myapp_v2f.net/r1">http://myapp_v2f.net/r1</a>
route('namedroute'):
    http://myapp_v2f.net/r1
HTML::link(route('namedroute')):
    <a href="http://myapp_v2f.net/http://myapp_v2f.net/r1">http://myapp_v2f.net/http://myapp_v2f.net/r1</a>

I am thinking, that perhaps the HTML::link could issue a warning if the app name isn't valid and debug==true

The problem is exactly because of the underscore in your host name. Take a look at the Illuminate UrlGenerator class. It has a method called isValidUrl which validates the $path variable through:

filter_var($path, FILTER_VALIDATE_URL);

Since the underscore isn't valid, it fails. But I think a warning here doesn't make sense, since this actually has nothing to do with Laravel.