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fix: clarify hostname vs IP requirements for SIP trunk gateways #995

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fix: clarify hostname vs IP requirements for SIP trunk gateways #995

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18 changes: 11 additions & 7 deletions fern/advanced/sip/troubleshoot-sip-trunk-credential-errors.mdx
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Original file line number Diff line number Diff line change
Expand Up @@ -36,15 +36,18 @@ This is the most common cause of this error.

### What happens

Vapi's API accepts both hostnames (for example, `sip.example.com`) and IPv4 addresses (for example, `203.0.113.10`) in the `gateways[].ip` field. However, the underlying SBC only accepts IPv4 addresses. When you provide a hostname, the SBC rejects the gateway configuration.
Vapi's API accepts both hostnames (for example, `sip.example.com`) and IPv4 addresses (for example, `203.0.113.10`) in the `gateways[].ip` field. However, **hostnames only work for outbound-only gateways**. For inbound-enabled gateways, the SBC requires a numeric IPv4 address to match the origin of incoming SIP requests. When you provide a hostname for an inbound-enabled gateway, the SBC rejects the gateway configuration.

### How to check

Look at the value you passed in `gateways[].ip`. If it contains letters (for example, `sip.example.com`), it is a hostname. The SBC needs a numeric IPv4 address instead.
Look at the value you passed in `gateways[].ip` and the `inboundEnabled` setting:

- If `inboundEnabled` is `true` (the default) and `gateways[].ip` contains a hostname (for example, `sip.example.com`), this is the problem. Inbound gateways require a numeric IPv4 address.
- If `inboundEnabled` is `false` (outbound-only), hostnames are accepted and this is not the cause of your error.

### How to fix

Resolve the hostname to its IPv4 address, then use that IP directly.
If your gateway has inbound enabled, resolve the hostname to its IPv4 address, then use that IP directly.

<Steps>
<Step title="Look up the IP address">
Expand Down Expand Up @@ -76,7 +79,7 @@ Replace the hostname with the numeric IPv4 address in your gateway configuration
"ip": "203.0.113.10",
"port": 5060,
"outboundEnabled": true,
"inboundEnabled": false
"inboundEnabled": true
}
]
}
Expand All @@ -86,8 +89,9 @@ Replace the hostname with the numeric IPv4 address in your gateway configuration
</Steps>

<Note>
Always use the IPv4 address, not the hostname. If your provider's IP changes,
you need to update the gateway configuration.
Hostnames are supported for outbound-only gateways (`inboundEnabled: false`).
For inbound-enabled gateways, always use a numeric IPv4 address. If your
provider's IP changes, you need to update the gateway configuration.
</Note>

## Inbound enabled on an outbound-only trunk
Expand Down Expand Up @@ -157,7 +161,7 @@ The table below lists all available options for each entry in the `gateways` arr

| Option | Type | Default | Description |
| -------------------- | ------- | --------- | ------------------------------------------------------------------------------ |
| `ip` | string | (required)| IPv4 address of your SIP gateway. Must be a numeric IP address, not a hostname.|
| `ip` | string | (required)| Server address of your SIP gateway. Use a numeric IPv4 address for inbound-enabled gateways. Hostnames are accepted for outbound-only gateways (`inboundEnabled: false`).|
| `port` | number | `5060` | SIP signaling port. |
| `netmask` | number | `32` | Subnet mask for inbound IP matching. Valid range: 24 to 32. |
| `inboundEnabled` | boolean | `true` | Whether this gateway accepts inbound calls. Set to `false` for outbound-only trunks. |
Expand Down