
When the TS_DEBUG_NETSTACK_LOOPBACK_PORT environment variable is set, netstack will loop back (dnat to addressFamilyLoopback:loopbackPort) TCP & UDP flows originally destined to localServicesIP:loopbackPort. localServicesIP is quad-100 or the IPv6 equivalent. Updates tailscale/corp#22713 Signed-off-by: Jordan Whited <jordan@tailscale.com>