Installation guide

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Device Manager Guide, Cisco ACE 4700 Series Application Control Engine Appliance
OL-26645-02
Chapter 5 Configuring Virtual Servers
Configuring Virtual Servers
Hash URL The ACE selects the server by using a hash value based on the URL. Use this method to load balance
firewalls.
Enter values in one or both of the pattern fields:
• In the URL Begin Pattern field, enter the beginning pattern of the URL and the pattern string to
parse.
• In the URL End Pattern field, enter the ending pattern of the URL and the pattern string to parse.
Valid entries for these fields are unquoted text strings with no spaces and a maximum of 255
alphanumeric characters for each pattern you configure.
Least Bandwidth The ACE selects the server with the least amount of network traffic over a specified sampling period.
1. In the Assess Time field, enter the number of seconds for which the ACE is to collect traffic
information. Valid entries are integers from 1 to 10 seconds.
2. In the Least Bandwidth Samples field, enter the number of samples over which you want to weight
and average the results of the probe query to calculate the final load value. Valid entries are 1, 2,
4, 8, and 16 (integers from 1 to 16 that are also a power of 2).
Least Connections The ACE selects the server with the fewest number of connections.
In the Slowstart Duration field, enter the slow-start value to be applied to this predictor method. Valid
entries are integers from 1 to 65535, where 1 is the slowest ramp-up value.
The slow-start mechanism is used to avoid sending a high rate of new connections to servers that you
have just put into service.
Least Loaded The ACE selects the server with the lowest load based on information from SNMP probes.
1. In the SNMP Probe Name field, select the name of the SNMP probe to use.
2. In the Auto Adjust field, configure the autoadjust feature to instruct the ACE to apply the
maximum load of 16000 to a real server whose load reaches zero or override the default behavior.
By default, the ACE applies the average load of the server farm to a real server whose load is zero.
The ACE periodically adjusts this load value based on feedback from the server's SNMP probe and
other configured options.
Options are as follows:
– Average—Applies the average load of the server farm to a real server whose load is zero. This
setting allows the server to participate in load balancing, while preventing it from being
flooded by new connections. This is the default setting.
– Maxload—Instruct the ACE to apply the maximum load of 16000 to a real server whose load
reaches zero.
– Off—Instruct the ACE to send all new connections to the server that has a load of zero until
the next load update arrives from the SNMP probe for this server. If two servers have the same
lowest load (either zero or nonzero), the ACE load balances the connections between the two
servers in a round-robin manner.
3. In the Weight Connection field, check the check box to instruct the ACE to use the current
connection count in the final load calculation for a real server. When you configure this option, the
ACE includes the current connection count in the total load calculation for each real server in a
server farm. Clear the check box to reset the behavior of the ACE to the default of excluding the
current connection count from the load calculation.
Table 5-12 Predictor Methods and Attributes (continued)
Predictor Method Description / Action