Nortel Networks WEB OS 212777 - Manual (Page 166)

Web OS 10.0 Application Guide
166 n Chapter 6: Server Load Balancing
212777-A, February 2002
WAN Link Load Balancing
Wide Area Networking (WAN) is a telecommunications network system spread across a broad
geographic area. A WAN may be privately owned or rented, but the term usually means the
inclusion of public (shared user) networks, such as the telephone system. WANs can also be con-
nected through leased lines and satellites. WANs are typically composed of powerful routers and
switches that link business enterprises, universities, remote offices, and so on, around the world.
To handle the high volume of data on the Internet, some corporations are using more than one
Internet Service provider (ISP) as a way to increase reliability of Internet connections. Such
enterprises with more than one ISP are referred to as being multi-homed. In addition to reliabil-
ity, a multi-homed network architecture enables enterprises to distribute load among multiple
connections and to provide more optimal routing.
The WAN link load-balancing feature introduces additional resilience for networks in multi-
homed environment. When users want to control which WAN link the traffic traverses, WAN
link load balancing can be used to steer requests initiated within the user’s network and his/her
responses over the appropriate link at that moment in time.
How WAN Link Load Balancing Works
The Web switch uses redirection filters to redirect traffic initiated from within the user’s net-
work to a group of devices that exist at the other end of the WAN link (routers, for example).
These filters determine which link is the best at the time the request is generated. To ensure
that the responses traverse the same link, the source IP address of the request is translated to
one of the addresses that the selected ISP owns.
The design of WAN link load balancing is identical to standard redirection, except that it
substitutes the source IP address of each frame with the proxy IP address of the port to which
the WAN link is connected.
Configuring WAN Link Load Balancing
Before configuring the Web switch for WAN Link load balancing, make sure of the following:
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Disable NAT Web Cache Redirection. WAN Link load balancing and NAT Web Cache
Redirection cannot be configured on the same switch.
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Configure the load balancing metric for response time only.
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Do not configure your ports into trunk groups.
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Do not configure WAN link load balancing with two or more WAN links connected
through the same switch port. This feature uses the proxy IP address of the destination port
when translating the source IP address of the requests.