Main Page | See live article | Alphabetical index SYN (synchronize) is a type of packet used by the Transmission Control Protocol (TCP) when initiating a new connection to sychronize the clocks on the two connecting computers. A type of denial of service attack known as a SYN flood involves sending large numbers of SYN packets and ignoring the return, thereby forcing the server to keep track of a large number of half-open connections. This article is a stub. You can help Wikipedia by fixing it. This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.