We help IT Professionals succeed at work.

We've partnered with Certified Experts, Carl Webster and Richard Faulkner, to bring you two Citrix podcasts. Learn about 2020 trends and get answers to your biggest Citrix questions!Listen Now


Cisco Router-Tell which ports are currently open/VOIP??

cmmosman1 asked
Medium Priority
Last Modified: 2011-04-14
Is their any way to tell on a Cisco router which ports are currently open?  I'm trying to figure out which ports our Siemens VOIP phones are using. Outgoing traffic is being prioritized (LLQ) on the router but all traffic (incoming) originating from the offsite phone system is not so I’d like to be able to tell which ports it’s opening on the offsite phone system router.
Watch Question

Top Expert 2005

1. see the router config - if you not blocking particular ports with access lists - they all open
2. run portscan software - plenty on the web.


I guess I wanted to see which ports are in use and not necessarily which are open, sorry.  Is their someway to tell that?
Top Expert 2005

If you have NAT in the router - just enter command "show ip nat translations" and you will see all ports wich in use at the moment.

Also, it will be useful to use "show ip port-map" command to see list of port services available...


I unfortunetly don't have the router NATed....any other ideas?

Top Expert 2005

You can set up sniffer to listen on the router inside/outside interfaces, use Ethereal which is free and brilliant: http://www.ethereal.com/
Just connect router and PC with sniffer to the same hub (not switch) and see what applications/ports in use at the moment...

Ethereal PC

if just the signalling goes trought the router than SIP uses port 5060
but if also RTP and RTCP stream goes trought the router, it is much bigger issue, because the port for the rtp stream is dinamicly asigned, and you canot predict the port for rtp.



Since the traffic doesn't seem to be going over Cisco IOS H.323 ports 16385-3276 I just ended up matching any traffic destin to the ip addreess of the phone.  Thanks for all you help.
PAQed with points refunded (500)

Community Support Moderator

Not the solution you were looking for? Getting a personalized solution is easy.

Ask the Experts
Access more of Experts Exchange with a free account
Thanks for using Experts Exchange.

Create a free account to continue.

Limited access with a free account allows you to:

  • View three pieces of content (articles, solutions, posts, and videos)
  • Ask the experts questions (counted toward content limit)
  • Customize your dashboard and profile

*This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.


Please enter a first name

Please enter a last name

8+ characters (letters, numbers, and a symbol)

By clicking, you agree to the Terms of Use and Privacy Policy.