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Block (or Transfer) restricted or anonymous CLID using a SIP trunk

I have a client that is getting lots of prank calls by people calling from blocked or restricted phone #s.

Ideally I’d like to trap these calls and send them to a VM Box that says “call from a phone that is not blocked”

I’ve seen several posts here that talk about blocking specific #’s – but I’m not sure how to do that with blocked #’s


Everyone's tags (3)

Block (or Transfer) restricted or anonymous CLID using a SIP tru

Perhaps the SIP provider can?  Have you asked them?

I see CME has anonymous block for SIP, but not for SCCP, which UC5xx uses.....

anonymous block

To enable anonymous call blocking in a SIP phone template, use the anonymous block command in voice register template configuration mode. To return to the default, use the no form of this command.

anonymous block

no anonymous block

Syntax Description

This command has no arguments or keywords.

Command Default


Command Modes

Voice register template configuration (config-register-temp)

Command History

Cisco IOS Release

Cisco Product



Cisco CME 3.4

This command was introduced.

Usage Guidelines

This command blocks incoming calls in which the caller is not identified. To apply a template to a SIP phone, use the template command in voice register pool configuration mode.


The following example shows how to set anonymous call blocking in template 1:

Router(config)# voice register template 1

Router(config-register-temp)# anonymous block


Re: Block (or Transfer) restricted or anonymous CLID using a SIP

Hi Eric,

There is a way to do this, but it's not something you'd want to undertake on a live system. You could do it if building a system from scratch, certainly not using CCA and requires a thorough understanding of inbound/outbound dial-peers, dial-peer matching, number translations and voice security. It would also help if the Service Provider could prefix all incoming numbers with an Alphanumeric character sting such as AAA or similar for easy identification. You would need to disable the "permission term" dial peer. I've used the technique in reverse where I wanted to route calls out of certain trunk groups, based on the extension number making the call and COR was not practical.

Start with a router with no dial-peers configured.

The procedure would be:

1. An incoming call would always match a known incoming dial peer you have configured.

2. Instead of the call being routed to an extension or AA, you would then send the call out of a dial-peer with an H323 target of itself (the same router). At the same time using number translations to prefix the dialled number with for-example "AD". Use codec transparent on the dial-peers

At this point there is no incoming dial peer that matches calls arriving on the router with called numbers starting AD.

3. Configure a set of incoming H323 dial-peers based on "answer address". If the Answer address passes certain constraints, use number translations to strip the AD from the called number and route the call to the correct place - i.e. AutoAttendant, DID etc

4. Have an incoming H323 dial-peer with an answer address that matches . Use number translations to route the call to your special voice mail box.

As I said certainly not one for a live enviroment but the technique is certainly valid.

An "Anonymous Block" keyword would be alot simpler!


New Member

Re: Block (or Transfer) restricted or anonymous CLID using a SIP


the SIP provider says the can't block the calls.

I might try the anonymous block command


this just seems way to complex!

I'll let you know what happens when i try it.


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