Nortel Networks WEB OS 212777 - Manual (Page 414)

Web OS 10.0 Application Guide
414 n Chapter 15: Content Intelligent Switching
212777-A, February 2002
Content Precedence Lookup
The Layer 7 Precedence Lookup feature in Web OS allows you to give precedence to one Layer
7 parameter over another and selectively decide which parameter should be analyzed first.
The Content Precedence Lookup feature allows you to combine up to two Layer 7 load balanc-
ing mechanisms. You can specify which types of Layer 7 content to examine, the order in
which they are examined, and a logical operator (and/or) for their evaluation.
The following Layer 7 content types can be specified:
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URL SLB
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HTTP Host
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Cookie
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Browsers (User agent)
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URL hash
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Header hash
Using the above content types with the and and or operators, the Web switch is configured to
refine HTTP-based server load balancing multiple times on a single client HTTP request in
order to bind it to an appropriate server. Typically, when you combine two content types with
an operator (and/or), URL hash and Header hash are used in combination with Host, Cookie,
or Browser content types.
For example, the following types of load balancing can be configured using the Content Prece-
dence Lookup feature:
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Virtual host and/or URL-based load balancing
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Cookie persistence and URL-based load balancing
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Cookie load balancing and/or URL-based load balancing
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Cookie persistence and HTTP SLB together in the same service
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Multiple HTTP SLB process type on the same service
N OTE – Cookie persistence can also be combined with the Layer 7 content types. For more
information on cookie persistence, see Chapter 16, “Persistence .”
For example, the Content Precedence Lookup feature can be used in the following scenarios:
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If the client request is sent without a cookie and if no HTTP SLB is configured, then the
switch binds the request to the real server using normal SLB.
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If the client request is sent without a cookie, but HTTP SLB is configured on the switch,
then the request is bound to real server based on HTTP SLB.
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If the client request is sent with a cookie, and a real server associated to the cookie is
found in the local session table, then the request will stay bound to that real server.