[NTLUG:Discuss] how do i know if port 80 was blocked?

[MadHat]

On Fri, 2003-01-03 at 14:05, Philip Stetz wrote:
> --- m m <llliiilll at hotmail.com> wrote:
> > 
> > Hi all:
> > Is there any to find out if the port 80 was blocked?
> > IP 12.237.x.x from at&t
> > 
> > thanks
> > 
> 
> you can use nmap to do a port scan on that ip.  some
> sys admins may frown upon that though :)

Depending on how the router/firewall is configured, it may or may not
tell.  If it just drops the packets, you can't tell if it being blocked,
or his machine just doesn't have anything on port 80. 

If the router sends an ICMP prohibited message, nmap will show filtered,
but that is not always accurate, as some timeouts will show filtered as
well.  

If the router sends a reset it will just show closed, even though it may
be blocked.

To be 100% sure, start up a sniffer on the 12.237.x.x machine and then
telnet to port 80 to it from a machine on a different network and look
for the traffic in the sniffer.  If it shows up, it isn't blocked.  Of
course you can still use nmap, but that is overkill.  You can also use a
plethora of other tools like netcat or any other port scanner, but
telnet is easy and will do the trick.


-- 
MadHat at Unspecific.com
`But I don't want to go among mad people,' Alice remarked.
`Oh, you can't help that,' said the Cat: `we're all mad here...'
   -- Lewis Carroll - _Alice's_Adventures_in_Wonderland_