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Old 11-04-2004, 06:46 PM   #1
mfeoli
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Registered: Dec 2003
Distribution: Debian
Posts: 92

Rep: Reputation: 15
How to check if packets/ports are being filtered/blocked


Hi,

I have a firewall based on ipchains,

I placed it open to anything to test a software that needs access via some ports: TCP 4662 UDP 4672.

ipchains -L shows as follow:
$ ipchains -L

Chain input (policy ACCEPT):
target prot opt source destination ports
- icmp ------ anywhere anywhere any -> any
- udp ------ anywhere anywhere any -> any
- tcp ------ anywhere anywhere any -> any
Chain forward (policy MASQ):
target prot opt source destination ports
- icmp ------ anywhere anywhere any -> any
- udp ------ anywhere anywhere any -> any
- tcp ------ anywhere anywhere any -> any
Chain output (policy ACCEPT):
target prot opt source destination ports
- icmp ------ anywhere anywhere any -> any
- udp ------ anywhere anywhere any -> any
- tcp ------ anywhere anywhere any -> any

but the software keeps telling that the ports aren't open,

My suspition now are towards the CPE /ADSL router.

Is there a way to test which ports are passing through the CPE and which arent?

thanks
 
Old 11-05-2004, 06:27 AM   #2
HomeUser
LQ Newbie
 
Registered: Apr 2004
Posts: 19

Rep: Reputation: 0
I suppose you already tested with
telnet <ip-address> port,
(or site name if you are sure your DNS works)
and with traceroute.
There is a way to put every blocked packed in a log file by adding -log-level nn in the iptables commands.
 
  


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