Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 311)

Brocade Virtual ADX Server Load Balancing Guide 295
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Miscellaneous Layer 7 switching configurations
5
Layer 7 CSW pseudo stack client-side retransmission
handling
The Brocade Virtual ADX Content Switching (CSW) pseudo stack needs to store HTTP request
packets from the client before it is able to perform server selection. If the stored packets are not
acknowledged by the CSW pseudo stack and these packets get dropped before reaching the
server, they can be retransmitted by the client. However, there are cases when the Brocade Virtual
ADX needs to acknowledge those stored packets before forwarding them to the server. An example
of this is when the client’s HTTP request spans multiple packets, and the client expect an
acknowledgment before transmitting the remaining request packets. Upon receiving all request
packets, the Brocade Virtual ADX performs server selection and transmits all requests packets to
the server. Since the current CSW pseudo stack does not keep the stored packets once they are
sent out, they will never be transmitted if these packets get dropped. If this occurs, the client will
keep retransmitting the request for acknowledgement to the Brocade Virtual ADX, until the TCP
timeout expires. As a result, the client will notice that the HTTP transaction never gets completed.
The Brocade Virtual ADX supports handling of HTTP request retransmission with Layer 7 pseudo
stack. When the Layer 7 CSW pseudo stack retransmission handling is enabled, the Brocade
Virtual ADX acknowledges and stores the client TCP packets, and does not clear its buffer until the
request packets are acknowledged by the server. If the retransmission timer triggers before the
request packets are acknowledged, the Brocade Virtual ADX will resend the stored packets.
The same situation can happen at the server side traffic. If server response headers span multiple
packets, the Brocade Virtual ADX also needs to send the acknowledgment to the server. With this
feature enabled, the server-side retransmission is also supported. The Layer 7 CSW pseudo stack
retransmission handling feature is disabled by default.
Enabling the Layer 7 CSW client-side retransmission handling
To enable Layer 7 CSW pseudo stack retransmission handling feature, enter the command as
follows:
Virtual ADX(config)#server csw enable-retransmission
Syntax: [no] server csw enable-retransmission