Network Interfaces

nsINetworkLinkService.networkInterfaces lists the network interfaces of the device as nsINetworkInterface objects: name, MAC address, IP addresses and default gateways.

const linkService = Cc["@mozilla.org/network/network-link-service;1"]
  .getService(Ci.nsINetworkLinkService);
for (const intf of linkService.networkInterfaces) {
  console.log(intf.name, intf.mac, intf.ipv4, intf.ipv6, intf.gwv4, intf.gwv6);
}

Collection is only built with --enable-enterprise. In other builds, reading networkInterfaces throws NS_ERROR_NOT_IMPLEMENTED, assuming the service exists. When that is not the case, then existing NS_ERROR_NOT_AVAILABLE may be returned.

The list is only available in the parent process: reading it elsewhere throws NS_ERROR_NOT_AVAILABLE. Consumers must not forward it, or data derived from it, to child processes.

How the list is built

Each platform collects the interfaces on a background thread and keeps the result in a cache. Reading networkInterfaces copies that cache, so it never blocks on the system, but it can be empty right after startup and lag behind a network change for a few seconds.

        flowchart LR
  linux["Linux, Android<br/>NetlinkService"]
  mac["macOS<br/>nsNetworkLinkService"]
  win["Windows<br/>nsNotifyAddrListener"]
  cache[("Cached list")]
  api["networkInterfaces"]
  linux -- "address or route change" --> cache
  mac -- "IP configuration change" --> cache
  win -- "address change" --> cache
  cache -- "copy on read" --> api

Values

Attribute	Format	Example
`name`	System name; adapter friendly name on Windows	`eth0`, `en0`, `Wi-Fi`
`mac`	Six lowercase hex bytes	`02:00:5e:10:00:01`
`ipv4`, `gwv4`	Dotted quad	`192.168.1.1`
`ipv6`, `gwv6`	Compressed form of RFC 5952	`fe80::5a1d:d8ff:fe3c:ba90`

Addresses never carry a prefix length or an IPv6 zone (no %en0).
ipv4 and ipv6 include link-local addresses (169.254.0.0/16, fe80::/10).
mac keeps the first six bytes of longer hardware addresses, pads shorter ones with zeros, and is 00:00:00:00:00:00 when there is none, e.g. on a VPN tunnel.
Lists are unordered and may be empty.

Which interfaces are reported

Only interfaces that are up and not loopback:

Platform	Reported when
Linux, Android	running, not loopback, with at least one global address
macOS	up, running, not loopback, with an active link
Windows	operationally up, with a unicast address, not loopback and not a VMware `VMnet` adapter

Gateways

gwv4 and gwv6 hold the next hops of the default routes (0.0.0.0/0, ::/0) that go through the interface:

A gateway is listed under its own address family.
IPv6 gateways are usually link-local router addresses, learned from router advertisements.
A default route without a next hop, as on a point-to-point VPN, adds no gateway.
An interface without a default route has empty lists.

Platform	Source
Linux, Android	Netlink default routes with a gateway
macOS	Routing table entries with a `0.0.0.0` or `::` destination
Windows	Gateway addresses of the adapter