Set up a trunk

A trunk is a reusable connection to your SIP infrastructure. It holds your provider’s endpoint, the transport, and authentication. You create it once and attach numbers and DIDs to it.

Using 3CX, Bandwidth, Five9, NICE CXone, Telnyx, or Twilio? Follow that provider’s guide under SIP integrations in the sidebar. It covers the provider side and the exact values to enter here.

Prerequisites

An endpoint on your carrier, PBX, or SBC that Bland can reach over TLS on port 5061, with SRTP enabled
Firewall access to allow-list Bland’s signaling and media IPs
The numbers you will route, on your own carrier. Numbers bought from Bland can’t be attached to a trunk

Create a trunk

On the SIP tab, press Create trunk. The wizard names the trunk from the provider and endpoint, and every trunk it builds carries both directions. Rename it later on the trunk’s Configure tab.

The trunk is created at the Authentication step, not at the end. Pressing Create trunk there writes the trunk before you pick a single number. Leaving after that point leaves a real trunk behind with nothing attached.

Provider

Pick your provider and enter its SIP endpoint. The field accepts a hostname, an IP, a full SIP URI such as sip:user@host:5061;transport=tls, or shorthand such as tls://host. The wizard parses the host, port, and transport.The catalog has instructions for Twilio, Vonage, Asterisk / FreePBX, 3CX, Cisco UCM / CUBE, and RingCentral. For anything else, including Bandwidth and Telnyx, pick Other.Microsoft Teams can’t connect directly. Put a certified SBC between Teams and Bland, and enter the SBC’s address.

Discovery

Bland probes your endpoint. It resolves DNS (A, AAAA, and SRV records), sends SIP OPTIONS to common ports over UDP, TCP, and TLS, and detects your system, codecs, and methods.It then shows the recommended port and transport. You can skip discovery and enter settings yourself.

Firewall

The wizard lists the Bland IPs and ports to allow-list. The full reference is in Connection endpoints. Tick the confirmation box to continue.Cloud providers such as Twilio, Vonage, and RingCentral skip this step, because there is no firewall of yours to change.

Authentication

Choose how Bland and your server trust each other:

IP-based (recommended): your server trusts Bland’s IPs as SIP peers, and Bland trusts your endpoint by its source IP. No credentials to manage.
Registration-based: Bland registers with your server using a username and password. Generate password creates a strong one.

Then choose how outbound calls leave Bland:

Via Bland’s carrier (default): Bland’s carrier places the call to your SIP endpoint. Nothing else to set up.
Direct to your carrier (BYOC): Bland sends the call straight to your carrier, so termination runs on your own carrier contract. Your carrier must support TLS, and the caller IDs you dial from must be authorized on that account.

Under Outbound call credentials, enter the SIP username and password your carrier gave you. Bland uses them to answer a 401 or 407 challenge. They are optional with Bland’s carrier and required with direct routing.Press Create trunk.

Numbers

Add the numbers to route through the trunk, or skip and add them later from the trunk’s Numbers tab.

Complete

The trunk is live. Test connection at the top of the trunk page sends a SIP OPTIONS ping to your endpoint over TLS.

Attach numbers and DIDs

Numbers inherit the trunk’s endpoint, transport, and authentication, so you don’t repeat them per number.

Phone numbers are stored in E.164, for example +14155550100.
DIDs and extensions, such as 2001, are stored as written when the number is attached to a trunk.
Each number has its own inbound and outbound configuration.

Attach numbers from the trunk’s Numbers tab, or up to 100 at a time with POST /v1/sip/attach:

curl -X POST https://api.bland.ai/v1/sip/attach \
  -H "Authorization: Bearer <token>" \
  -H "Content-Type: application/json" \
  -d '{
    "phone_numbers": ["+14155550100", "2001"],
    "directions": [{ "type": "inbound" }, { "type": "outbound" }],
    "service": "sip",
    "trunk_id": "<trunk-id>"
  }'

The response lists configured numbers, and failed numbers with a reason for each. Then assign an agent to each number. Under Phone numbers, press Configure on the number and pick the agent under Assignment.

Inspect a call

Open a trunk’s Overview tab and select a call to see its SIP trace: every message on every leg, as a sortable table or a ladder diagram, with full headers and SDP. Copy or export it to share with your carrier. The call log beside it shows each call’s direction, status, SIP response code, and duration.

Advanced configuration

PATCH /v1/sip/config saves failover servers, codec preferences, and alert thresholds for a number. Bland stores these settings but does not apply them to calls yet, and there is no dashboard control for them:

Calls use the single endpoint on the trunk. There is no automatic failover.
Calls use Bland’s standard codec list, whatever order you save.
No SIP-specific alerts are sent.

Do it with the API

Validate an endpoint

POST /v1/sip/parse-destination parses a destination into its host, port, user, and transport:

curl -X POST https://api.bland.ai/v1/sip/parse-destination \
  -H "Authorization: Bearer <token>" \
  -H "Content-Type: application/json" \
  -d '{ "input": "sip:your.provider.com:5061;transport=tls" }'

Run discovery

POST /v1/sip/discover runs the full probe. The recommended object in the response has the port, transport, and detected_system. One discovery runs per organization at a time. Poll a long one with GET /v1/sip/discover/status.

curl -X POST https://api.bland.ai/v1/sip/discover \
  -H "Authorization: Bearer <token>" \
  -H "Content-Type: application/json" \
  -d '{ "host": "sip.example.com" }'

Get the IPs to allow-list

GET /v1/sip/firewall-ips returns your region’s IPs and ports.

curl https://api.bland.ai/v1/sip/firewall-ips \
  -H "Authorization: Bearer <token>"

Use registration authentication

Set auth_mode in the inbound direction of POST /v1/sip/attach:

{
  "type": "inbound",
  "auth_mode": "register",
  "register_auth": {
    "username": "my-trunk",
    "password": "a-strong-password"
  }
}

The response includes register_password_for_pbx, a one-time derived password to configure in your PBX. GET /v1/sip/generate-password returns a strong, PBX-safe password between 8 and 256 characters.

Create a named or one-direction trunk

The wizard always builds a two-way trunk with a generated name. POST /v1/sip/trunks takes a name and a single direction.

Check a number's health

GET /v1/sip/status returns the health of a number’s SIP configuration.

curl 'https://api.bland.ai/v1/sip/status?phone_number=%2B14155550100' \
  -H "Authorization: Bearer <token>"

Common failures

Attaching a number fails

Numbers bought from Bland can’t be attached to a trunk. Attach numbers that live on your own carrier.

Test connection fails but calls work

Test connection sends SIP OPTIONS over TLS. Some carriers don’t answer OPTIONS from Bland. Place a test call to be sure.

Inbound calls are rejected with 603 Decline

The number your carrier sends isn’t attached to a trunk in your organization. Attach it in E.164 format, with the +.

Inbound calls are challenged with 407

Bland doesn’t trust the IP the call came from. Check that the trunk endpoint matches the server that sends your calls. If your server’s public IP changed, contact Bland support.

Next steps

Transfers

Send callers to a DID, extension, or SIP URI.

Network and security

Regions, IPs to allow-list, and TLS and SRTP.

Docs for agents: llms.txt

Getting started

Build

Monitor

Dispatch

Configure

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Support

AI Agents & MCP

Platform Information

Bland Enterprise

Legacy

Set up a trunk

Prerequisites

Create a trunk

Attach numbers and DIDs

Inspect a call

Advanced configuration

Do it with the API

Common failures

Next steps

Transfers

Network and security

​Prerequisites

​Create a trunk

​Attach numbers and DIDs

​Inspect a call

​Advanced configuration

​Do it with the API

​Common failures

​Next steps

Transfers

Network and security

Prerequisites

Create a trunk

Attach numbers and DIDs

Inspect a call

Advanced configuration

Do it with the API

Common failures

Next steps