Sends to addresses no card has on the new arp-routed network (ping on the LAN and behind a router, two UDP datagrams, one behind a failing one): frames and calls. ScenarioNetwork builds routers and their interfaces. Measured: ARP asks twice, a round trip each, then host unreachable; the thread that waits is the ping's caller, the router's IP thread, or the node's transport thread per protocol, which blocks the next send. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>