Showing results for 
Search instead for 
Did you mean: 

Cisco SX20 : receiving incoming calls from unknown sources


Dear Readers and Guru's,


We are using a Cisco SX20 with ISDN Link due to some our regional offices still using ISDN connection, anyways, this is working fine. The only problem I am experiencing is the fact there are a lot of unknown established calls, examples below ;


1003, 3500, 100, 7070, 1003 and etc..


the format of the incoming call will start with an unknown number and followed by our SIP number ; 1003@***.**.*.***:5060

I want to permanently block this unknown callers as this is so annoying during our Video Conferencing meeting it keeps on ringing on the screen..


I was told that it has something to do with the network/firewall settings but honestly i don't know where to start.

i had attached a screenshot of the unknown numbers we are receiving.


TIA guys.

7 Replies 7



In codec , can you try the following config. change and check if the unknown calls are stopped ?

system configuration -> SIP -> ListenPort -> Off


Deva G

If we disable SIP Listen Port, calls cannot send out.

"Off" the SIP Listen Port and "On" the Outbound in SIP Profile.

Should be OK then.

Thanks for your information.

Btw, is there any impacts for incoming and outgoing calls if we disable SIP Listen Port?

When i do this, the SX Device loses registration, immediately.  

After Sip >Off,Now ok ,Now we not receive unwanted call.Thanks

Wayne DeNardi
VIP Advisor VIP Advisor
VIP Advisor

Sounds very much like your device is being probed by a SIP Scanner such as SIPVicious.  There are many threads in these forums that discuss how to block this type of call, ie

The simplest way to block the calls is to turn the SIP ListenPort setting to OFF.

You can do this via the Web Interface as suggested by Deva, or through the CLI with the "xConfiguration SIP ListenPort: Off" command.

Please remember to rate responses and to mark your question as answered if appropriate.

Please remember to mark helpful responses and to set your question as answered if appropriate.
Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community:

Recognize Your Peers