---
name: "rad.conf"
section: "5"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["openbsd"]
url: "https://new.carta.tech/rad.conf"
---

# rad.conf(5)

router advertisement daemon configuration file

## NAME

**rad.conf** – router advertisement daemon configuration file

## DESCRIPTION

The [rad(8)](/rad/8.md) daemon is an IPv6 router advertisement daemon.

The **rad.conf** config file is divided into the following main sections:

- Macros

  Definitions of variables that can be used later, simplifying the configuration file.

- Global configuration

  Global settings for [rad(8)](/rad/8.md). These are used as default values for **interface** definitions and can be overwritten in an **interface** block.

- Interfaces

  [rad(8)](/rad/8.md) sends IPv6 router advertisement messages. This section defines on which interfaces to advertise prefix information and their associated parameters.

Additional configuration files can be included with the **include** keyword.

### Macros

A macro is defined with a command of the form *name*=*value*. The macro *name* can contain letters, digits, and underscores and cannot be a reserved word (for example, **interface**). Within unquoted arguments, the string $*name* is later expanded to *value*.

### Global configuration

The global configuration section sets defaults for router advertisement messages. These can be overwritten in interface blocks.

- **default** **router** (**yes**\|**no**)

  Act as a default router or not. The default is **yes**.

- **dns** {*option* *...*}

  Add a DNS router advertisement option to communicate network provided nameservers. In a **dns** block, a **search** option or at least one **nameserver** option is required, whereas specifying the **lifetime** is optional:

  - **lifetime** *seconds*

    The number of seconds the dns options are valid after receiving a router advertisement message. The default is 3600 seconds.

  - **nameserver** (*address*\|{*address* *...*})

    IPv6 address or list of IPv6 addresses of DNS name servers.

  - **search** (*domain*\|{*domain* *...*})

    Domain or list of domains for the [resolv.conf(5)](/resolv.conf/5.md) search list.

- **hop** **limit** *hops*

  Specify the diameter of the internet. The default is 0, meaning unspecified by this router.

- **managed** **address** **configuration** (**yes**\|**no**)

  If set to **yes**, indicate that stateless address configuration prefixes are not available and hosts should consult DHCPv6. The default is **no**.

- **mtu** *bytes*

  The MTU option is used in Router Advertisement messages to ensure that all nodes on a link use the same MTU value in those cases where the link MTU is not well known. The default is 0, meaning unspecified by this router.

- **nat64** **prefix** *prefix* \[{*option* *...*}\]

  Add a PREF64 router advertisement option to communicate prefixes used for Network Address and Protocol Translation from IPv6 to IPv4 (NAT64). If *prefix* is specified without a prefix length, its default is 64.

  **nat64** **prefix** options are as follows:

  - **lifetime** *seconds*

    The number of seconds the nat64 prefix option is valid after receiving a router advertisement message. A value of zero indicates to not use the prefix anymore. The maximum is 65528 seconds. The default is 3600 seconds.

- **other** **configuration** (**yes**\|**no**)

  If set to **yes**, hosts should consult DHCPv6 for additional configuration like NTP servers or DNS name servers. The default is **no**.

- **router** **lifetime** *seconds*

  The number of seconds this router is a valid default router after receiving a router advertisement message. The default is 3600 seconds.

- **router** **preference** (**high**\|**medium**\|**low**)

  Indicate whether to prefer this router over other default routers. The default is **medium**.

- **reachable** **time** *number*

  The time, in milliseconds, that a node assumes a neighbor is reachable. The default is 0, meaning unspecified by this router. This option is ignored by [slaacd(8)](/slaacd/8.md) and cannot be set on OpenBSD IPv6 hosts.

- **retrans** **timer** *number*

  The time, in milliseconds, between retransmitted Neighbor Solicitation messages. The default is 0, meaning unspecified by this router. This option is ignored by [slaacd(8)](/slaacd/8.md) and cannot be set on OpenBSD IPv6 hosts.

- **source** **link-layer** **address** (**yes**\|**no**)

  Add a source link-layer address option to router advertisement messages, to communicate the link-layer address of the sending interface. The default is **yes**.

### Interfaces

This section contains a list of interfaces or interface groups to send advertisements on. At least one **interface** is required.

- **interface** *name* \[{*prefix* *...*}\]

  Options set in the global section can be overwritten inside an interface block. In addition an interface block can contain a list of prefixes:

  - \[**no**\] **auto** **prefix** \[{*option* *...*}\]

    - **prefix** *prefix* \[{*option* *...*}\]

    The default is to discover prefixes to announce by inspecting the IPv6 addresses configured on an interface. This can be disabled with **no** **auto** **prefix**. If *prefix* is specified without a prefix length, its default is 64.

    **prefix** options are as follows:

    - **autonomous** **address-configuration** (**yes**\|**no**)

      This prefix can be used to generate IPv6 addresses. The default is **yes**.

    - **on-link** (**yes**\|**no**)

      This prefix is considered on-link. The default is **yes**.

    - **preferred** **lifetime** *seconds*

      The preferred lifetime (pltime) in seconds for addresses generated from this prefix. The default is 2700. This option is ignored if the prefix is discovered from a network interface and it has a lower preferred lifetime.

    - **valid** **lifetime** *seconds*

      The valid lifetime (vltime) in seconds for addresses generated from this prefix. The default is 3600. This option is ignored if the prefix is discovered from a network interface and it has a lower valid lifetime.

## FILES

- */etc/rad.conf*

  [rad(8)](/rad/8.md) configuration file.

- */etc/examples/rad.conf*

  Example configuration file.

## EXAMPLES

With the following example configuration, [rad(8)](/rad/8.md) will pick a prefix from the ix1 interface and send router advertisements on it:

```
interface ix1
```

## SEE ALSO

[ractl(8)](/ractl/8.md), [rad(8)](/rad/8.md), rc.conf.local(8)

## HISTORY

The **rad.conf** file format first appeared in OpenBSD 6.4.