Objective
Customers typically already have an extension scheme in place. When building out a new domain, we should strive to follow the customer’s existing extension numbering scheme as closely as possible to avoid confusion and support smoother adoption.
Symptoms
- VIP: Extension Numbering Standards and Server Placement Guidelines
-
What is the reserved extension range for the domain
Procedure
Recommended and Reserved Extension Range
Recommended User Extension Ranges
When creating a new domain, use the following extension schemes for user extensions:
- 100–998
- 1000–8999
- 10000–199999
- 100000–199999
IMPORTANT: These ranges are guidelines. If the customer already has a numbering plan in place, prioritize matching their existing structure whenever possible.
Reserved Extension Ranges
Do not assign these as user extensions
The following extensions are reserved and should not be assigned to individual users:
- 111
- 211
- 311
- 411
- 511
- 611
- 711
- 811
- 833
- 911
- 933
- 999
- 5000 & 5001
- 9000–9999
NOTE: On x11 Extensions
x11 numbers are set to only show the outbound Caller ID on X11 numbers. They must show outbound Caller ID and PSAP (or location) information.
Recommended: Call Flow Extension Ranges
| Feature / Object | Recommended Extension Range |
|---|---|
| Call Queues | 8500–8999 |
| Auto Attendants | 8500–8999 |
| Conference Lines | 8500–8999 |
| Call Parks | 9000–9999 |
| Paging Units (Snom, CyberData) | 7777 & 8888 (most common) |
Server Placement Requirement for Devices
When adding devices, place them on one server for the entire account: USW, USC, or USE.
- If there are multiple locations, choose the server closest to the main location.
- Geo IP routing will automatically apply when calls are placed.
- Keeping devices tied to a single server helps ensure features work consistently across the account.
- The backend automatically distributes calls, features, and presence across servers, eliminating the need to manually assign devices to specific servers.
- Confirm the customer’s existing extension numbering plan before provisioning new users or call flow objects.
- Validate that reserved extensions are not assigned to user endpoints during onboarding and audits.
- When troubleshooting feature inconsistencies (presence, BLF, intercom/paging behavior, etc.), verify that devices were not split across USW/USC/USE servers.
Escalation Information
Escalation Information: SD1
If you need additional assistance, contact Crexendo Support at 855-211-2255 or email us at support@crexendo.com
Change Log
| Date | Description |
|---|---|
| May 21, 2026 | Article revamped |