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A black hole, in the context of computer networks, is a place where incoming packets are destroyed or discarded without informing the sender or recipient of their failed delivery.
Data packets are sent to a black hole when they are directed to an offline or disconnected router. When this happens, all packets forwarded to that router are discarded and lost. Routers are dumb and cannot transmit status notifications to the sender and are virtually invisible to the entire network.
A computer communication network is composed of many different networks. Each is managed by a router that enables the routing of communications toward or away from that domain. If a particular router goes offline, a condition is created in which all the packets directed toward that router (or the connecting network) are lost as soon as they reach the point in the network where that router is installed. This is known as a black hole in the computer network.
Black holes may occur due to other circumstances. For instance, when a host in unreachable due to its offline state, or a recipient address belongs to a bogus IP address, an unconfigured router cannot handle such packets. This also creates black holes, where data packets traveling toward them and traffic routed toward them are lost.