port forwarding help!

Benjamin Scott bscott at ntisys.com
Fri Dec 24 23:20:01 EST 2004


On Fri, 24 Dec 2004, at 8:14pm, jfreeman at gmail.com wrote:
> I have a WRTG54 Wireless Router.

  I just bought one of those yesterday myself.  They run Linux internally,
and are supposed to be rather hackable.

> Where I'm having problems is port 80!... No matter what I try, on the
> router or on the laptop, I cannot seem to get requests to port 80
> forwarded, by the router, to the laptop.

  Some ISPs block TCP/80 inbound.  That may be your problem.

  Another possible cause is that since the router's management interface is
web-based, it sees TCP/80 inbound on the public interface as an attempt to
connect to the management interface, and blocks it for security reasons.

  You might try: On the router, enable HTTPS for management, make sure that
works, and then disable HTTP management.  That might help.

> I see the hits in the router log..

  Hmmmm.  That would seem to indicate the ISP isn't the problem.

> but I can't figure out whether:
> 
> a) they're being held at the router or
> b) forwarded by the router but stopped by the laptop.

  As root on the laptop, run:

	tcpdump -n -i eth0 -f 'port 80'

If your laptop's LAN interface isn't "eth0", change that accordingly.  The
"-n" tells tcpdump not to lookup names, and the "-f 'port 80'" is a filter
expression telling tcpdump to show you only traffic to or from port 80.  
Then run your remote test, to see if your laptop sees anything.

  You might also try attaching your laptop directly to the ISP feed
(disabling all other services and/or using a host-based firewall first) and
see if you can connect that way.

> Oh, and MERRY CHRISTMAS, etc.!

  Happy Kwanukahmas.  ;-)

-- 
Ben Scott <bscott at ntisys.com>
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