TCP provides various TCP extensions to improve performance over high-bandwidth and high-speed data paths. One such extension
is the TCP window-scaling option. The loose-checking option for TCP window-scaling turns off strict checking of the window-scaling
option described in RFC 1323.
A larger window size is recommended to improve TCP performance in network paths with large bandwidth-delay product characteristics
that are called Long Fat Networks (LFNs). TCP window scaling expands the definition of the TCP window to 32 bits and then
uses a scale factor to carry this 32-bit value in the 16-bit window field of the TCP header. The window size can increase
to a scale factor of 14. Typical applications use a scale factor of 3 when deployed in LFNs.
A firewall implementation enforces strict checking of the TCP window-scaling option. A firewall drops SYN/ACK packets
that have the TCP window-scaling option if it was not offered in the initial synchronization (SYN) packet for the TCP three-way
handshake. The window-scale option is sent only in a SYN segment, which is a segment with the SYN bit on. Therefore, the
window scale is fixed in each direction when a connection is opened.
Use the tcp window-scale-enforcement loose command to disable the strict checking of the TCP window-scaling option in TCP SYN segments.