Forwarding

When a packet goes out, the hard part is not whether there is a destination address. The hard part is why so many routers in the network all seem to agree, at that moment, to send it in one direction. Links fail, exits change, prefixes get summarized, default routes act as fallback, and policy may deliberately avoid the path that looks shortest. If one of those decisions disagrees with the others, packets disappear into black holes, detour, flap, or fall into a loop.