Nortel Web OS 10.0, Application Manual

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Web OS 10.0 Application Guide
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Chapter 11: High Availability
212777-A, February 2002
What Happens When a Switch Fails
Assume that the user performing an e-commerce transaction has selected a number of items
and placed them in the shopping cart. The user has already established a persistent session on
the top server in
Figure 11-14 . The user then clicks the Submit button to purchase the items.
At this time, the active switch fails. With stateful failover, the following sequence of events
occurs:
1. The backup switch (Switch 2) becomes active.
2. The incoming request is redirected to Switch 2.
3. When the user clicks Submit again, the request is forwarded to the correct server.
Even though Switch 1 has failed, the stateful failover feature prevents the client from having to
re-establish a secure session. The server that stores the secure session now returns a response
to the client via Switch 2.
Figure 11-14 Stateful Failover Example when the Master Switch Fails
Router
Web Switch 1
Failed
Layer 2
Switch
Servers
Web Switch 2
Active
IP: A
IP: B
Internet
Traffic is redirected
to Switch 2
Clients