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The interface MAC address can be set with the link.address option of an interface. If the option is not set, the interface's MAC address will be configured to a default value. For physical interfaces this is their permanent MAC address. For virtual interfaces ifstate derives a reproducible MAC address.

Reproducible MAC Addresses

The reproducible MAC addresses are based on the output of the SHAKE256 extendable-output function. The input for SHAKE256 for each interface is build by concatinating the following values depending on the ifstate config:

EBNF for SHAKE256 input string

No implicit link.address config will be enforced if:

  • the interface does not support ethernet addressing (ipip, sit, vti, …) or
  • the mac_seed option for the current netns is set to null

Examples for a host with the machine-id of c5826ec0bb89fe5ca3af4e183d51e636:

  • a VLAN subinterface vl42 in a netns with the mac_seed set to ha-service01 will use the digest of the following string: SHAKE256("link\000\000ha-service01\000vl42") ⇒ ee:65:a3:17:74:99
  • a VLAN subinterface vl42 in the root netns will use the digest of the following string: SHAKE256("link\000c5826ec0bb89fe5ca3af4e183d51e636\000\000vl42") ⇒ 9e:12:25:18:4e:31
  • a VLAN subinterface vl42 in the netns foo will use the digest of the following string: SHAKE256("link\000c5826ec0bb89fe5ca3af4e183d51e636\000foo\000vl42") ⇒ 0a:13:9b:fc:bc:6d