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. If we are starting from scratch, we should use this list as a base.
Symptoms
- VIP: Extension Numbering Standards and Server Placement Guidelines
- What is the reserved extension range for the domain
-
Extension Best Practices
Procedure
Recommended and Reserved Extension Range
Recommended User Extension Ranges
When creating a new domain, use the following extension schemes for user extensions:
- 100–999
- 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 | If you need assistance finding food, paying housing bills, or other essential services |
| 311 | Non-emergency phone number that people can call in many cities to find information about services, make complaints, or report problems like graffiti or road damage |
| 411 | Information |
| 511 | Local transportation and traffic information |
| 611 | Reserved for local telephone company repair |
| 711 | TTY |
| 811 | Call before you dig |
| 833 | Toll-free |
| 911 | Emergency |
| 933 | Used to test 911 location |
| 988 | Suicide hotline |
| 5000 | |
| 5001 | |
| 9000-9999 | Call Parks |
NOTE: 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.
TIP: Our preferences
ATAs and Faxes = 200+ or 2000+ (look up for exceptions). Set up as an Elite User.
EXAMPLE: To help with troubleshooting, an example setup for call flows would be the following:
For Call Queues, Auto Attendants, and Conference lines, build these on 8500-8999
For Call Parks, build these on 9000-9999
For Paging units (Snom, Cyberdata), 7777 and 8888 are the most common
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 assign devices to specific servers manually.
- 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 |
|---|---|
| Aug 1, 2026 | Merge Extension Best Practices (3873127) |
| May 21, 2026 | Article revamped |