Port is open but I am unable to connect

Jason Opperisano opie at 817west.com
Thu Sep 9 14:20:47 CEST 2004

On Thu, 2004-09-09 at 06:17, Jacob Friis Larsen wrote:
> With the changes I still can't connect. I also use bonding if that's 
> important.

dunno about bonding...might be important.

> <script>
> #!/bin/sh
> # Modules
> modprobe ip_conntrack_ftp
> modprobe ip_nat_ftp
> # Defaults
> iptables -P INPUT DROP
> iptables -P FORWARD DROP
> iptables -P OUTPUT DROP
> # Flush
> iptables -t nat -F POSTROUTING
> iptables -t nat -F PREROUTING
> iptables -t nat -F OUTPUT
> iptables -F
> # STATE RELATED for router
> iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
> iptables -A OUTPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
> # Localhost
> iptables -A INPUT -i lo -j ACCEPT
> iptables -A OUTPUT -o lo -j ACCEPT
> # Open ports on router for server/services
> #iptables -A INPUT -s -j ACCEPT -p tcp --dport 20 -m state 
> --state NEW
> iptables -A INPUT -s -j ACCEPT -p tcp --dport 21 -m state 
> --state NEW
> iptables -A INPUT -s -j ACCEPT -p tcp --dport 22 -m state 
> --state NEW
> iptables -A INPUT -j ACCEPT -p tcp --dport 25 -m state --state NEW
> iptables -A INPUT -j ACCEPT -p tcp --dport 80 -m state --state NEW
> iptables -A INPUT -j ACCEPT -p tcp --dport 143 -m state --state NEW
> iptables -A INPUT -j ACCEPT -p tcp --dport 993 -m state --state NEW
> </script>

just to clarify a point--the services your trying to connect to *are*
running locally on the machine running netfilter, correct?  the only
reason i ask, is because the comment "Open ports on router for
server/services" leads me to believe that "router" and "server" are two
different machines.  if "server" is behind "router" you should be using
FORWARD filter rules, not INPUT...

anyways...at this point--i'd recommend:

  iptables -A INPUT -j LOG --log-prefix "FW DROP IN: "
  iptables -A OUTPUT -j LOG --log-prefix "FW DROP OUT: "
  iptables -A FORWARD -j LOG --log-prefix "FW DROP FWD: "

and then "tail -f /var/log/messages" and try to connect.  the logs will
tell you why the firewall is dropping the traffic.


Jason Opperisano <opie at 817west.com>

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