SIP trunk vs SIP registration: which your carrier needs

Both are SIP trunks — the difference is how the carrier knows it's really you. A registration trunk logs in with a username and secret; an IP-authentication trunk is trusted because the calls come from a whitelisted IP. If your server has a fixed public IP, IP auth is usually the simpler choice.

Two ways to authenticate

A SIP trunk is the connection between your VICIdial server and your Carrier over SIP (Session Initiation Protocol). Whatever the carrier calls their product, your server has to prove it's allowed to send and receive calls. There are two ways to do that.

With registration, your server sends a SIP REGISTER message to the carrier's SIP registrar using a username and secret. The carrier remembers where you are and accepts calls tied to those credentials. In VICIdial this is the carrier's Registration string — the exact register line you paste into the carrier entry.

With IP authentication, no credentials change hands per call. You give the carrier your server's static public IP, they whitelist it, and they trust any call that arrives from that address. There's no register line at all — you just set the host to the carrier's IP.

From VICIdial's point of view the two trunks look almost identical — same protocol, same dialplan, same in-group routing. The only structural difference is whether the carrier entry carries a register line. Everything downstream of the carrier, from the DID (direct inward dialing) handling to your campaigns, behaves the same way either way.

Which one your carrier needs

Your carrier decides this, not you — but most carriers offer both, so the decision often comes down to your network:

• Static public IP. If your server's IP never changes, IP auth is cleaner. There's nothing to re-register, no credentials to leak, and one less thing that can silently expire.
• Changing or dynamic IP. If your address moves, registration is the way — the carrier finds you wherever you are because your server checks in with credentials.
• Carrier policy. Some carriers simply require one or the other. If they hand you a username and secret, they expect registration; if they ask for your IP, they're setting up IP auth.

Deciding quickly

flowchart TD
  A[Setting up a carrier] --> B{Carrier gave you user and secret?}
  B -->|Yes| C[Use SIP registration]
  B -->|No, asked for your IP| D{Is your server IP static?}
  D -->|Yes| E[Use IP authentication]
  D -->|No| F[Ask carrier for registration]
  C --> G[Paste register line in carrier entry]
  E --> H[Set host to carrier IP, no register line]

If you're unsure, ask the carrier one question: do you authenticate my server by credentials or by IP? Their answer tells you which trunk to build.

There's also a maintenance angle worth weighing. A registration trunk has one more moving part — the registration itself, which can drop if your credentials change, the carrier resets your account, or the network blips. When a registration lapses, calls stop until your server re-registers. An IP-auth trunk has nothing to lapse: as long as your address stays the same and the carrier keeps it whitelisted, the trunk just works. For a server that never moves, that's one fewer thing to monitor.

Where this fits

Both approaches plug into the same carrier entry in VICIdial. For the full walkthrough, see the VICIdial carrier integration guide. For a side-by-side of the two methods in more detail, see register vs IP auth.

VICIfast gives every server a fixed public IP, so IP-auth carriers are easy to point at it — and a box is online in under 40 seconds. Check pricing to spin one up and connect your carrier.