Running Multiple Carriers with Failover in VICIdial

A single carrier is a single point of failure. When that provider has a bad hour, your whole campaign stalls and your agents sit idle. The fix is to wire up more than one carrier and let calls roll from a primary trunk to a backup when the primary isn't answering. VICIdial supports this with nothing more than a second carrier record and a slightly smarter dialplan.

This post shows how to add a backup carrier, how failover decides to switch, and the gotchas that bite people who set it up once and never test it.

Add the second carrier first

Each provider is its own carrier record with its own SIP trunk, account entry, and auth method. Set up your backup Carrier exactly like the primary: account entry, codec, context, and either a registration string or an IP whitelist. Confirm it works on its own by routing a test call straight to it before you chain the two together. A backup you never proved out is not a backup.

Once both peers show up in the Asterisk CLI, you can build the Dialplan logic that ties them together.

How failover decides to switch

In a basic Failover setup, the dialplan tries the primary trunk's Dial line, then checks the result. If the call comes back with a busy or unreachable response, the next dialplan step dials the same number out the backup trunk instead. The deciding signal is the SIP response code, codes like 503 (service unavailable) or 408 (timeout) mean the primary couldn't take the call, so the dialplan moves on.

The rollover, visualized

flowchart TD
  A[Outbound call] --> B[Dial primary trunk]
  B --> C{Primary answered?}
  C -->|Yes| D[Call connects]
  C -->|Trunk failed| E{Backup active?}
  E -->|Yes| F[Dial backup trunk]
  E -->|No| G[Call fails]
  F --> H{Backup answered?}
  H -->|Yes| D
  H -->|No| G

Keep the patterns from colliding

Because both carriers may match the same dialed pattern, you need to be deliberate about which one Asterisk reaches first. With true failover you chain the steps inside one extension so the order is explicit. If instead you want each provider to handle different traffic, give them distinct leading digits, which leans on a Dial prefix per carrier rather than automatic rollover. Decide up front whether you want failover (same number, second try) or split routing (different numbers, different trunks).

• Failover: one pattern, primary Dial then backup Dial in sequence.
• Split routing: different prefixes send different traffic to each carrier.
• Hybrid: split by default, but let one fail over to the other on trunk failure.

For the underlying routing mechanics, read how outbound calls find the right carrier. And if your goal is cost rather than uptime, least-cost routing uses the same multi-carrier idea to pick the cheapest path. The full setup lives in the carrier integration guide.

Test it on purpose

The only way to trust failover is to break the primary on purpose and watch calls roll to the backup. Set the primary carrier to Active=N for a few minutes during a quiet window, place a test call, and confirm it leaves the backup peer. Then turn the primary back on. Do this before you ever need it, not during an outage.

VICIfast gives you a dedicated server you fully control, so you can run two carriers and prove your failover whenever you like. A branded dialer is live in under 40 seconds. See our pricing to set up redundant carriers today.