[Gllug] Port filtering question

[salsaman at xs4all.nl]

On Wed, September 29, 2010 05:32, Walter Stanish wrote:
>> I have been struggling with this for a few days now. I am trying to set
>> up
>> an icecast server on my desktop machine. Everything seems to be working
>> fine, except that nobody can connect to the port.
>>
>> ....
>>
>> I am not running any kind of firewall or packet filtering firewall
>> software on the PC as far as I can tell, as I generally use the router
>> as
>> the firewall. So is this a bug in the router, an ISP issue or is there
>> something on the desktop machine doing this ?
>
> One way to find out which part of your network infrastructure filters a
> port
> is to run a traceroute with that port selected.  Whilst traceroute is a
> cool
> hack, and old versions tended not to use TCP, modern implementations
> such as that in recent versions of nmap will allow you to specify UDP or
> TCP ports, along with a host of other options.
>
> For a simple example, you could use:
>  nmap --traceroute -PT -p80 your.target.host.com
>
> I seem to remember that icecast doesn't normally run on port 80 by
> default, a quick google suggests '8000'.
>
> - Walter
> --
> Gllug mailing list  -  Gllug at gllug.org.uk
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>
>

Yes in fact I was running icecast on port 8000 and then laetr on 8001. In
both cases, forwarding the corresponding port on the router shows
(filtered), whereas opening other ports like 22 (ssh) and 80 shows (open)
or (closed) depending on whether there is a server listening on that port
or not. Unforwarded ports all show (closed).

Cheers,
Salsaman.










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