Coyote Point Systems Equalizer Especificaciones descargar pdf (Pagina 265)

The previous sections describe how the connection timeouts work when the once only flag is disabled on a cluster;

that is, when Equalizer is examining every set of headers received on a connection. The once only option, when

enabled, specifies that Equalizer will examine only the first set of headers received on a connection. This has the

following effects on connection timeouts:

l If you have once only enabled, as soon as the initial transaction (client request and server response) on a

connection completes, the connection goes into “streaming” mode and the client timeout is no longer used

for this connection. Equalizer does not parse any additional client requests received on the connection. The

server timeout is used for the remainder of the connection, and is reset whenever data is received from

either side of the connection.

l If you have once only disabled as described in the previous sections, and multiple requests are being sent

on the same connection, the client timeout starts counting down again as soon as a new request is received

from the client.

Layer 4 Connection Timeouts

Connections to Layer 4 clusters are received by Equalizer and forwarded with little processing. Equalizer simply

rewrites the source and/or the destination IP addresses, as appropriate for the cluster, and sends the packet to the

server specified by the cluster’s load balancing policy. For Layer 4 TCP clusters, a connection record is kept for

each connection so that address translation can be done on the packets going between the servers and clients.

The Layer 4 connection timeouts specify how long a connection record is kept by Equalizer.

Layer 4 TCP clusters use the idle timeout and stale timeout parameters. The idle timeout can be set at the global

and cluster levels, while stale timeout can be set at the global level only. The parameters affect how Equalizer

manages Layer 4 connection records:

l Connection records need to be removed in cases where the connection is not closed by the client or server,

and is left idle. If no data has been received on a connection from either the client or the server after the time

period specified by the idle timeout has elapsed, then Equalizer removes the connection record for that

connection. Any data received from either client or server resets the idle timer.

Note that when using Direct Server Return (DSR), the time that a connection record is maintained is

determined by adding the idle timeout for the cluster to the sticky time . This additional time is necessary

when using DSR, since no server responses are routed through Equalizer (and therefore cannot restart the

idle timeout to keep the connection open). For more information on DSR, see "Configuring Direct Server

Return" on page 313.

l In other cases, a connection may be initiated but never established, so the connection record goes “stale”

and must be removed. If a client fails to complete the TCP connection termination handshake sequence or

sends a SYN packet but does not respond to the server’s SYN/ACK, Equalizer marks the connection as

incomplete. The stale timeout is the length of time that a connection record for an incomplete connection is

maintained.

When Equalizer reclaims a connection, it sends a TCP RST (reset) packet to the server, enabling the server to

free any resources associated with the connection. (Equalizer does not send a TCP RST to the client when

reclaiming a connection.)

Reducing the stale timeout can be an effective way to counter the effects of SYN flood Denial of Service attacks

on server resources. A stale timeout of 10.0 (see table below) would be an appropriate value for a site under SYN

flood attack.

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