DHCPv6 server for difficult clients

This is a probably not RFC-compliant DHCPv6 server for a very narrow use case: assigning fixed IPv6 addresses based entirely on the client's MAC address. Note that this DHCPv6 server does not respect or account for leases.

You should only use this if:

• You have clients you can't configure to use regular SLAAC with addresses following the usual EUI-64 scheme

• You still need these clients to have stable IP addresses, even if they don't keep any state (frequent OS wipes!)

We use this for macOS and a HITL where reprovisioning isn't 100% reliable, so we want them to get the same IP address even if none of the scripts have run.

Notes:

• this daemon may or may not work correctly with relay agent forwarding.
• this daemon will not try to issue HTTP Boot instructions if the template is an empty string. If you don't want that, feel free to PR it into an optional setting.

Usage

go build .
sudo ./dhcpv6macd -interface enp2s0 -base-address 2001:db8:0123:4567:: -http-boot-url-template 'http://netboot.target/?mac={{.MAC}}'

...where the template can use these parameters:

• MAC -- the MAC address of the netbooting device
• BaseAddress -- the same value as passed in the CLI arguments
• Payload -- a base64 encoded JSON blob about the booting device, for example eyJhcmNoaXRlY3R1cmVzIjpbIkVGSSB4ODYtNjQgYm9vdCBmcm9tIEhUVFAiXX0= which is decodes to:

{
  "architectures": ["EFI x86-64 boot from HTTP"]
}

There is also a NixOS module in the flake.nix.

See the flake.nix for a NixOS test involving router and a client.

Address allocation scheme

The prefix is assumed to be at least a /80. The MAC address is simply concatenated onto the prefix.

If the DHCPv6 Solicit request does not have a MAC address, we fall back to loading the MAC from an eui64 link-local IP. Note that this only works if the Soliciting system encodes their MAC in their link local address via EUI-64 (privacy/stable-privacy LLAs won’t work.)

What's not inside

This does not provide:

• Router advertisements (we use systemd-networkd for this)
• DHCPv4 (we use systemd-networkd for this)
• Options for DNS, NTP, etc

License

This code is GPL-3, and based on Adguard's AdGuardHome DHCPv6 server: https://github.com/AdguardTeam/AdGuardHome/blob/167b1125113c86e6304471d80d983c17f0f707e3/internal/dhcpd/v6_unix.go.