black hole

Black Hole in a internetwork is a router that goes down and whose absence from the network is not detected by other routers.

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What is Black Hole (in computer networking)?

In an internetwork, a black hole is a router that goes down and whose absence from the network is not detected by other routers. Packets that are forwarded to the black hole are dropped; they never reach their destination, and they give no indication to the stations sending them that this is the case - therefore, the data is lost.

Normally, a router will issue an «ICMP Destination Unreachable» message when it cannot forward a packet. However, with a black hole, these messages are not generated, so the user doesn’t know that data is being permanently lost.

If static routing is being used, a black hole persists until the affected router is brought back on line or until other static routers have their routing tables reconfigured to take the downed router into account. If dynamic routing is used, other routers soon detect the presence of the black hole and adjust their routing tables accordingly to favor other paths.