Question

I don’t know if there is a way to ping a target outside my LAN proxy which accepts only Http requests through a squid proxy… I read somewhere that one way to deal with such problem is to use a http tunnel so that the proxy still sees the request as a Http request. Can I use this to ping,say, http://www.google.com which otherwise is giving the following error because the firewall is rejecting the request:

$ ping www.google.com
ping: unknown host www.google.com

If so how is it done…?

I have installed httptunnel.Any help in how to use it will be much appreciated.

Answer 1

No. Ping and traceroute make use of lower layer network protocols (ICMP and/or UDP, in particular, which are layer 4 protocols) and will not work over an HTTP (layer 7) tunnel. In any case, even if you could convince the HTTP proxy to open a raw TCP session for you (which is how some HTTP tunneling works) you would not receive the necessary packets to confirm that the host is reachable. (ICMP echo reply, in the case of ping, or the time-to-live expired ICMP packets in the case of traceroute)

To test for connectivity in this situation, I think the best you can do is an HTTP “ping”. (Try to establish an HTTP connection with the remote host and see if it works.) For example, you could do something like:

$ http_proxy=http://webproxy.example.com:3128 \
> curl -I http://google.com/ > /dev/null 2>&1 \
> && echo success || echo failure

Assuming you have curl installed, this would print “success” if google.com is reachable through your proxy and “failure” if not.