Nortel Web OS 10.0, Application Manual

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Web OS 10.0 Application Guide
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Chapter 6: Server Load Balancing
212777-A, February 2002
The Web switch, with SLB software, acts as a front-end to the servers, interpreting user session
requests and distributing them among the available servers. Load balancing in Web OS can be
done in the following ways:
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Virtual server-based load balancing
This is the traditional load balancing method. The switch is configured to act as a virtual
server and is given a virtual server IP address (or range of addresses) for each collection of
services it will distribute. Depending on your switch model, there can be as many as 256
virtual servers on the switch, each distributing up to eight different services (up to a total
of 2048 services).
Each virtual server is assigned a list of the IP addresses (or range of addresses) of the real
servers in the pool where its services reside. When the user stations request connections to
a service, they will communicate with a virtual server on the switch. When the switch
receives the request, it binds the session to the IP address of the best available real server
and remaps the fields in each frame from virtual addresses to real addresses.
IP, FTP, RTSP, IDS, and static session WAP are examples of some of the services that use
virtual servers for load balancing.
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Filtered-based load balancing
A filter allows you to control the types of traffic permitted through the switch. Filters are
configured to allow, deny, or redirect traffic according to the IP address, protocol, or Layer
4 port criteria. In filtered-based load balancing, a filter is used to redirect traffic to a real
server group. If the group is configured with more than one real server entry, redirected
traffic is load balanced among the available real servers in the group.
Firewalls, WAP with RADIUS snooping, IDS, and WAN links use redirection filters to
load balance traffic.
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Content-based load balancing
Content-based load balancing uses Layer 7 application data (such as URL, cookies, and
Host Headers) to make intelligent load balancing decisions.
URL-based load balancing, browser-smart load balancing, and cookie-based preferential
load balancing are a few examples of content-based load balancing.