Updates tailscale/corp#18960
iOS uses Apple's NetworkMonitor to track the default interface and
there's no reason we shouldn't also use this on macOS, for the same
reasons noted in the comments for why this change was made on iOS.
This eliminates the need to load and parse the routing table when
querying the defaultRouter() in almost all cases.
A slight modification here (on both platforms) to fallback to the default
BSD logic in the unhappy-path rather than making assumptions that
may not hold. If netmon is eventually parsing AF_ROUTE and able
to give a consistently correct answer for the default interface index,
we can fall back to that and eliminate the Swift dependency.
Signed-off-by: Jonathan Nobels <jonathan@tailscale.com>
In prep for most of the package funcs in net/interfaces to become
methods in a long-lived netmon.Monitor that can cache things. (Many
of the funcs are very heavy to call regularly, whereas the long-lived
netmon.Monitor can subscribe to things from the OS and remember
answers to questions it's asked regularly later)
Updates tailscale/corp#10910
Updates tailscale/corp#18960
Updates #7967
Updates #3299
Change-Id: Ie4e8dedb70136af2d611b990b865a822cd1797e5
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Updates #8022
Updates #6075
On iOS, we currently rely on delegated interface information to figure out the default route interface. The NetworkExtension framework in iOS seems to set the delegate interface only once, upon the *creation* of the VPN tunnel. If a network transition (e.g. from Wi-Fi to Cellular) happens while the tunnel is connected, it will be ignored and we will still try to set Wi-Fi as the default route because the delegated interface is not getting updated as connectivity transitions.
Here we work around this on the Swift side with a NWPathMonitor instance that observes the interface name of the first currently satisfied network path. Our Swift code will call into `UpdateLastKnownDefaultRouteInterface`, so we can rely on that when it is set.
If for any reason the Swift machinery didn't work and we don't get any updates, here we also have some fallback logic: we try finding a hardcoded Wi-Fi interface called en0. If en0 is down, we fall back to cellular (pdp_ip0) as a last resort. This doesn't handle all edge cases like USB-Ethernet adapters or multiple Ethernet interfaces, but it is good enough to ensure connectivity isn't broken.
I tested this on iPhones and iPads running iOS 17.1 and it appears to work. Switching between different cellular plans on a dual SIM configuration also works (the interface name remains pdp_ip0).
Signed-off-by: Andrea Gottardo <andrea@tailscale.com>
Jonathan Nobels
Brad Fitzpatrick
Andrea Gottardo