port probing

acetylcholine · 2006-06-29 03:36:46

I have an iptables.rules based firewall.

So basically, I open every port that I use with something like
-A open -p udp --dport 5353 -j ACCEPT

I recently installed avahi and it was blocked by the firewall. I googled some and figured out that I needed to open port 5353

Is there a way to probe what ports a process is trying to access (in order to know which ones to open)?

T-Dawg · 2006-06-29 10:08:27

take a look at nmap

Bebo · 2006-06-29 10:31:39

You can also use netstat -natp or lsof -i to find out what addresses and ports are used by processes on your local machine.

On the Avahi FAQ it says that you need to allow traffic to and from UDP port 5353. Did you do that, or do you only allow traffic in one direction?

Bebo · 2006-06-29 17:03:43

D'oh, I missed the -u switch for netstat. It's needed if you want to see UDP ports as well: netstat -natup

acetylcholine · 2006-06-30 03:01:19

Thanks guys. The outgoing traffic should be covered by the established/related rule that I have in there.

Bebo · 2006-06-30 07:54:59

Maybe I'm misinterpreting what you say - "the established/related rule that I have in there" sound like singular. You'll have to put an ACCEPT rule in the INPUT and OUTPUT tables both. But maybe that's not the issue here

acetylcholine · 2006-07-01 00:56:35

Yeah, you're right. I DO only have it input... but I have:

-A OUTPUT -j open
# there is a similar line for input, straight from the wiki :)

and then

# mt-daapd and the daap protocol (needed for avahi out)
# heh, turns out i needed more ports :P
-A open -p tcp --dport 3689 -j ACCEPT
-A open -p udp --dport 3689 -j ACCEPT

# avahi-daemon
-A open -p tcp --dport 5353 -j ACCEPT
-A open -p udp --dport 5353 -j ACCEPT

This way the open chain I made goes to input and output both.

Good eye!! Thanks again, this issue is resolved now.

Bebo · 2006-07-01 01:21:10

Good to hear!

For clarification (although slightly unnecessary), when I said "INPUT and OUTPUT tables" above, I actually meant chains, not tables. Oh, well

Arch Linux

#1 2006-06-29 03:36:46

port probing

#2 2006-06-29 10:08:27

Re: port probing

#3 2006-06-29 10:31:39

Re: port probing

#4 2006-06-29 17:03:43

Re: port probing

#5 2006-06-30 03:01:19

Re: port probing

#6 2006-06-30 07:54:59

Re: port probing

#7 2006-07-01 00:56:35

Re: port probing

#8 2006-07-01 01:21:10

Re: port probing

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