4.2 Desired state

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On every reconcile netd computes, for each interface, what it should look like. That desired state is a link state, an MTU, a set of addresses and a set of routes. It is derived from the interface's verdict, its profile, and its clients' current state. During the first INIT-REBOOT it also includes the provisional IPv4 kernel state described in §2.1; netd keeps no general record of what it applied.

4.2.1 By verdict #

  • Loopback, or an IGNOREd interface: there is no desired state, and netd plans nothing for the interface.
  • DOWN: the link down, with no addresses and no routes.
  • JOIN: the link up, and everything below.

4.2.2 The metric #

Every route netd adds for an interface carries the interface's metric: the profile's Route.Metric when it is set, otherwise 600 for a wireless interface and 100 for anything else.

4.2.3 The MTU #

The profile's Mtu.Value when set. Otherwise, with Mtu.Offered, the lease's MTU (DHCP option 26), else the routers' advertised MTU (§6.1). Otherwise no MTU is desired and the link's MTU is left as it is.

4.2.4 IPv4 addresses #

  • every IPv4 entry of Address.Static, at its prefix;
  • the lease's address at the lease's prefix (§5.3), when a lease is held;
  • while the first INIT-REBOOT is pending, the requested address at its already-installed prefix (§2.1);
  • the link-local address (§5.5) at prefix 16, only when the client has fallen back to one and no lease is held and the profile has no static address of either family.

The order in which they are listed, or written in Address.Static, has no effect. netd adds the addresses an interface lacks in ascending address order (§4.3), and the kernel makes an address primary only when the interface holds no other address in the same subnet, so the first one added in a subnet is its primary. Of two statics in one subnet written 10.0.0.9/24, 10.0.0.3/24, both added in one pass, 10.0.0.3 is the primary.

While a lease that carried a broadcast address (option 28) is held, that broadcast is the one netd sets on every IPv4 address it adds to the interface: the lease's own address, and a static added in that time, whatever its subnet (§4.3).

4.2.5 IPv4 routes #

  • The default route goes via Route.Gateway's IPv4 entry when it is set. Otherwise, with Route.Offered, it goes via the lease's gateway: the first router of option 3, or, when the lease carried classless routes, the gateway of the classless 0.0.0.0/0 route. With neither, there is no IPv4 default route.
  • Classless static routes (option 121) with a prefix above zero are added, each via its gateway, only with Route.Offered.

During the first INIT-REBOOT, existing netd-marked IPv4 routes accompany the provisional address when Route.Offered is enabled. The profile's explicit gateway and current metric still take precedence (§2.1).

Route.Gateway is used as written; netd does not check that the gateway is on a subnet the interface has. A gateway the kernel cannot reach makes the route's add fail on every reconcile, logged each time (§11).

4.2.6 IPv6 addresses #

  1. every IPv6 entry of Address.Static, at its prefix, preferred, with a prefix route;
  2. every address router discovery currently wants (§6.2): stable-privacy and temporary addresses, each deprecated or not, each with or without a prefix route according to the prefix's on-link flag.

4.2.7 IPv6 default route #

Via Route.Gateway's IPv6 entry when it is set. Otherwise, with Route.Offered, via the default router router discovery has chosen (§6.1). With neither, there is no IPv6 default route.

4.2.8 Not desired #

netd never desires the kernel's own IPv6 link-local address, the kernel's prefix routes, or any route without netd's protocol mark. Those are outside what reconciliation compares (§4.3).

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