Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 307)

Brocade Virtual ADX Server Load Balancing Guide 291
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Miscellaneous Layer 7 switching configurations
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The default TCP window size is 8000 bytes. Setting the TCP window size to 1460 bytes causes a
client to send only one packet before waiting for the Brocade Virtual ADX to send an ACK, assuming
a Maximum Segment Size (MSS) of 1460 bytes. This setting applies only to SYN ACK and ACK
packets sent from the Brocade Virtual ADX to the client. The Brocade Virtual ADX does not modify
the TCP window size for traffic sent from real servers to clients by way of the Brocade Virtual ADX.
Preventing the Brocade Virtual ADX from sending an ACK to the client
You can configure the Brocade Virtual ADX not to send an ACK back to the client after the Brocade
Virtual ADX receives enough data from the client to select a real server. For example, if you enable
this feature in a URL switching configuration, and the Brocade Virtual ADX has received the entire
URL in a request, it does not send an ACK to the client after receiving the last packet. Withholding
the ACK prevents the client from sending further data to the Brocade Virtual ADX, increasing the
efficiency of the Layer 7 content buffer.
To cause the Brocade Virtual ADX not to send an ACK to the client after it has received enough
information to select a real server in a Layer 7 switching configuration, enter the following
command.
Virtual ADX(config)#server l7-dont-ack-last-packet
Syntax: server l7-dont-ack-last-packet
HTTP 1.1 support
The Brocade Virtual ADX has HTTP 1.1 support for Layer 7 switching and the Server Connection
Offload (HTTP Connection Proxy) features. These features help reduce TCP connection overhead by
offloading the management of TCP connections from application servers and allowing them to
dedicate resources for handling application transactions. These features significantly increase the
performance and capacity of back-end servers, minimize the number of round trips between users
and servers, reduce the bandwidth cost, and improve the Web experience of users.
HTTP was originally designed for simple text documents with embedded images that contain
hyperlinks to other documents. For each hyperlinked image, HTTP 1.0, by default, creates a
separate TCP connection, even if the images are all on the same server. In comparison, HTTP
version 1.1 allows a TCP connection or keepalive connection to remain open until all consecutive
requests and responses are complete. This technique is called persistent connection.
Persistent connection is enabled by default on HTTP 1.1 but is disabled by default in HTTP 1.0. For
HTTP 1.0, Web browsers must explicitly insert the HTTP header "Connection: keepalive" to enable
persistent or keepalive connections.
This release introduces two modes to support persistent connections: TCP offload mode and
keepalive mode. Both modes try to maintain and reuse keepalive connections on both the client
side and the server side.
TCP offload mode allows a request from one connection on the client side to re-use any established
connection on the server side. TCP offload mode offloads the management of TCP connections
from servers so they can dedicate resources to serving HTTP requests instead of managing
connections.
The re-use of open connections causes the source IP address and port of the request to be
translated from the original connection on the client side to a connection on the server side.
Consequently, a server cannot distinguish between clients simply by the source IP address of the
connections. If servers need to distinguish between clients’ source IP addresses, the keepalive
mode is recommended. It reuses the connections on the server side for application requests from