Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 267)

Brocade Virtual ADX Server Load Balancing Guide 251
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NOTE
The real server ID range is limited to 1024-1+the maximum number of real servers that can be
configured on the Brocade Virtual ADX. For example, if the maximum server limit is 16384, then the
valid real server ID range is from 1024 to 1024-1+16384=17407.
If you specify a server group ID, you can optionally specify a cookie name. When you specify a
cookie name, the Brocade Virtual ADX performs cookie switching on packets matching the rule,
which ensures that packets matching the rule go to the same real server within the server group.
Configuring the persist action
The persist action causes the Brocade Virtual ADX to send requests with similar content to the
same server when the specified rule is matched. When a rule is matched, the Brocade Virtual ADX
uses the content that matched the rule, in combination with a specified persistence method, to
select a server or server group to which to send the packet.
When a rule is associated with the persist action, a server or server group is selected as follows.
1. An incoming packet matches a configured CSW rule. For example, a CSW rule matches if an
incoming packet contains a cookie header field with the string “ServerID” as shown in the
following.
Virtual ADX(config)#csw-rule r1 header "cookie" search "ServerId"
The persist action can then be used in conjunction with the above CSW rule.
2. The Brocade Virtual ADX examines the matched content to determine the persist string. The
persist string contains the portion after the matched string that the Brocade Virtual ADX uses,
(along with the persist method) to select a real server (or server group) to which to send the
packet.
For example, in CSW rule r1 defined above, the matched content could be something like:
“ServerID=2”
Then, you can specify that the persist string be a segment of the matched content, starting
from a specified offset from the matched string (ServerID) and lasting for a specified length. In
the example above, if you specify an offset of “1” and a length of “1”, the persist string would
be “2”.
3. The Brocade Virtual ADX uses the persist string along with the configured persist method to
select a real server or group. By default, the Brocade Virtual ADX uses a hash-to-bucket persist
method to select a real server.