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# syntheticDNSAnswerIPv4Prefix

An IPv4 address prefix the relay uses to handle address info requests.

```
var syntheticDNSAnswerIPv4Prefix: String? { get set }
```

## Discussion

The value of this property is an address prefix, such as `192.0.2.0/24`. The relay manager uses this prefix to synthesize DNS answers for apps that use `getaddrinfo()` to resolve domains included in [`matchDomains`](/documentation/NetworkExtension/NERelayManager/matchDomains).

---

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