Overview of the call block list

Here are few benefits with this feature:

  • Webex Calling customer administrators can block incoming PSTN calls from numbers which are either spam or harassing. You can configure policies for an organization to block calls from one of the following numbers:

    • Configured numbers, for example: telemarketing callers or collection agencies

    • Known offenders such as disgruntled customers or ex-employees

    Blocking these calls help to reduce time in answering these calls, and protect the users from security threats or harassment.

  • Webex Calling rejects an external (PSTN) call coming in from blocked numbers, which are defined in the call block list. The callers are disconnected without hearing any announcement from Webex Calling. The calling numbers (coming from the PSTN trunks) are matched against the locally configured E164 patterns that is configured on Control Hub. For a successful match and call rejection, specify the calling number coming from the PSTN trunk in an equivalent E164 format. If the number schema used by your PSTN provider is non-E164, use the normalization rules at the Local gateway (for on-premise PSTN trunks) before sending the calls to Webex Calling.

  • Webex Calling can block calls in these scenarios:

    • Calls from anonymous numbers where the calling information isn’t available in the SIP From/P-Asserted-Id headers.

    • Calls with the presentation status marked as private. (The Privacy header is marked as id).

  • You can make an outbound call to the blocked numbers.

Create a block list

Configure a block list with numbers that can’t make incoming calls to your organization.


From the administrator view in https://admin.webex.com, go to Services > Calling.


Go to Service settings and scroll down to Call Block List.

You can add or remove phone numbers, country codes, or other patterns to the call block list. Ensure that the numbers and patterns are in E164 format.

  • Block calls with no caller ID—This option blocks incoming calls from PSTN without calling line information (Caller ID).

  • Block calls from hidden private numbers—This option blocks all calls from callers with private numbers or hidden identities.


Select Add to add numbers or patterns to block from calling the user's organization. The Add numbers to call block list window displays.

Follow these guidelines for adding numbers or patterns:

  • Enter patterns in E164 format.

  • Wildcards include the use of ! which represents a sequence of one or more digits.

  • X represents a single number (0-9).

You can add up to 200 numbers or patterns per organization. To add numbers in bulk, select Import CSV.

Numbers and patterns added to the block list is visible above the input field. Each number is validated as you enter them.

When you don’t enter any blocked numbers, a notification stating that there are no current blocked numbers added to this customer organization displays.


Click Save, to save the number. To remove a number, select . Save is enabled after entering the first valid number.

A list with all the blocked numbers displays. Click Delete, to delete an entry or use Clear all, to delete all numbers in the block list. A notification displays to confirm the action.

Troubleshoot blocking inbound spam calls

Use these steps to troubleshoot issues with blocking inbound spam calls. If the functionality isn’t working, then use the potential workarounds or solutions to resolve the issue.

Issue: Webex Calling doesn’t block incoming PSTN calls although the numbers are configured in the Call Block List.


  • Check the configured patterns in the Control Hub under Call Block List.

    1. Ensure that the E164 number pattern exactly matches the calling number that you’re trying to block.

    2. When using a wildcard pattern X, the number of digits must match with the number of X characters that you’ve configured.

      For example: If you want to block all numbers coming in from NPA-NXX 212-505, then use an E164 format of +1212505XXXX.

  • Check with your PSTN provider on the use of E164 numbering formats. If the provider is using National numbering schemes, then deploy the normalization rules at the Local Gateway trunk before sending the incoming PSTN call to Webex Calling.

    A sample normalization rule (IOS-XE SIP Profile to transform the From Header into an E164 format) for reference:

    1. Incoming SIP INVITE (received at Local Gateway) over the incoming PSTN Trunk:

      INVITE sip:12125052000@ SIP/2.0 
      Via: SIP/2.0/UDP;branch=z9hG4bK14fcef5a;rport 
      Max-Forwards: 70 
      From: sip:17326991000@;tag=as3f62ecae 
      To: sip:61295032222@ 
      Contact: sip:17326991000@
    2. Normalized SIP INVITE (sent to Webex Calling) from LGW

      INVITE sip:12125052000@ SIP/2.0 
      Via: SIP/2.0/UDP;branch=z9hG4bK14fcef5a;rport 
      Max-Forwards: 70 
      From: sip:+17326991000@;tag=as3f62ecae 
      To: sip:61295032222@ 
      Contact: sip:17326991000@
    3. SIP Profile applied on IOS-XE Dial peer towards Webex Calling:
      voice class sip-profiles 1 
      request INVITE sip-header From modify "ip:17" "ip:+17" 

For details on SIP Profiles in IOS-XE, see:Cisco Unified Border Element Configuration Guide Through Cisco IOS XE.