Книга: Iptables Tutorial 1.2.2

Shutdown and abort

Shutdown and abort

The SCTP connection is finally closed by either an ABORT chunk or by a graceful SHUTDOWN chunk. SCTP doesn't have a half-closed state as TCP, in other words one side can not continue sending data while the other end has closed its sending socket.

When the user/application wants to close the SCTP socket gracefully, it tells the protocol to SHUTDOWN. SCTP then sends all the data still in its buffers, and then sends a SHUTDOWN chunk. When the other end receives the SHUTDOWN, it will stop accepting data from the application and finish sending all the data. Once it has gotten all the SACK's for the data, it will send a SHUTDOWN ACK chunk and once the closing side has received this chunk, it will finally reply with a SHUTDOWN COMPLETE chunk. The whole session is now closed.

Another way of closing a session is to ABORT it. This is an ungraceful way of removing an SCTP association. When a connecting party wants to remove an SCTP association instantaneously, it sends an ABORT chunk with all the right values signed. All data in the buffers et cetera will be discarded and the association will then be removed. The receiving end will do the same after verifying the ABORT chunk.

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