TCP Flags

Figure 10-4 shows the eight TCP flags in the TCP header that are defined in RFCs 793 and 3168.

The eight TCP flags in the TCP header

Figure 10-4. The eight TCP flags in the TCP header

The TCP flags are defined as follows:

  • CWR (congestion window has been reduced). Indicates that the sending host has received a TCP segment with the ECE flag set. The congestion window is an internal variable maintained by TCP to manage the size of the send window. For more information, see Chapter 12.

  • ECE (TCP peer is ECN-capable). Indicates that a TCP peer is ECN-capable during the TCP 3-way handshake and to indicate that a TCP segment was received on the connection with the ECN field in the IP ...

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