radvd.conf

typical radvd.conf file structure and its key directives for configuring radvd (Router Advertisement Daemon) on a Linux system:

Overview of radvd.conf

File Location

  • Location: The radvd.conf file is typically located in /etc/radvd.conf on most Linux distributions.

Basic Structure

  • Global Configuration: The configuration file starts with global settings that apply to all interfaces, followed by interface-specific configurations.

Example Configuration

Here’s a simplified example of a radvd.conf file:

interface eth0 {
    AdvSendAdvert on;
    MinRtrAdvInterval 3;
    MaxRtrAdvInterval 10;
    AdvLinkMTU 1500;
    AdvDefaultPreference high;

    prefix 2001:db8:1234:5678::/64 {
        AdvOnLink on;
        AdvAutonomous on;
        AdvRouterAddr on;
    };

    RDNSS 2001:db8:aaaa:bbbb::1 {
        AdvRDNSSLifetime 1800;
    };

    DNSSL example.com {
        AdvDNSSLLifetime 1800;
    };
};

Directives Explanation

  • interface eth0 { ... }: Defines the configuration for the eth0 interface.

    • AdvSendAdvert on;: Enables sending Router Advertisement messages.

    • MinRtrAdvInterval, MaxRtrAdvInterval: Minimum and maximum intervals between sending RA messages.

    • AdvLinkMTU: Specifies the Maximum Transmission Unit (MTU) for the interface.

    • AdvDefaultPreference: Sets the default preference for routes advertised by this router.

  • prefix Directive: Configures the IPv6 prefix to advertise on the network.

    • AdvOnLink, AdvAutonomous, AdvRouterAddr: Specifies whether the prefix is on-link, autonomous (used for autoconfiguration), and if the router should use its address as the default gateway.

  • RDNSS and DNSSL Directives: These advertise Recursive DNS Server (RDNSS) and DNS Search List (DNSSL) information respectively.

    • AdvRDNSSLifetime, AdvDNSSLLifetime: Specifies how long the DNS information is valid.

Additional Considerations

  • Multiple Interfaces: You can configure multiple interfaces by repeating the interface block with different interface names (eth1, wlan0, etc.).

  • Security: Ensure radvd is only running on authorized routers and that access to RA messages is secured to prevent unauthorized advertisements.

Applying Changes

After modifying radvd.conf, you typically restart the radvd service to apply the changes:

sudo systemctl restart radvd

Testing and Verification

  • Use tools like tcpdump or wireshark to capture IPv6 traffic and verify that clients are receiving the correct Router Advertisement messages (radvd sends) with the configured parameters.

Conclusion

Understanding and correctly configuring radvd is crucial for IPv6 network deployments, ensuring that hosts can autoconfigure their IPv6 addresses and access network services seamlessly. Always refer to the radvd documentation and your specific network requirements when configuring radvd.conf.

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