Setting The Window Scale Factor - Cisco 4700M Configuration Manual

Chapter 4 Configuring TCP/IP Normalization and IP Reassembly Parameters
Configuring a Connection Parameter Map for TCP/IP Normalization and Termination

Setting the Window Scale Factor

The TCP window scaling feature adds support for the Window Scaling option in
RFC 1323. We recommend that you increase the window size to improve TCP
performance in network paths with large bandwidth, long-delay characteristics.
This type of network is called a long fat network (LFN).
The window scaling extension 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. You can increase the window size to a maximum scale
factor of 14. Typical applications use a scale factor of 3 when deployed in LFNs.
For Layer 7 connections (where the ACE terminates the connection), the ACE
forwards the original window scale factor from the client to the server. The ACE
sends the window scale factor that you configure in the SYN-ACK to the client.
The ACE window scale factor must match the server window scale factor or the
tcp-options command must be set to clear the window scale option. Otherwise,
unexpected results may occur. For more information about the tcp-options
command, see the "Configuring How the ACE Handles TCP Options" section.
For Secure Sockets Layer (SSL) connections or for configurations where the
WAN optimization RTT is set to zero (see the "Setting How the ACE Applies TCP
Optimizations to Packets" section), window scale mismatches between the ACE
and a server are allowed. For all other connections, the ACE window scale factor
must match the server window scale factor.
To set the TCP window scale factor, use the set tcp window-scale command in
parameter map connection configuration mode. The syntax of this command is as
follows:
set tcp window-scale number
The number argument is an integer from 0 to 14. The default is 0.
For example, to set the TCP window scale factor to 3, enter:
host1/C1(config-parammap-conn)# set tcp window-scale factor 3
To reset to the default value of 0, enter:
host1/C1(config-parammap-conn)# no set tcp window-scale
Cisco 4700 Series Application Control Engine Appliance Security Configuration Guide
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