Extreme Networks Px Series - Manual (Page 68)

6-10 Px Series Application Switch Installation and Configuration Guide
• The client transmits its first TCP request (A) to www.mybank.com at its
publicly-known VIP address, 64.1.1.7.
• The Px series application switch responds (B) on behalf of 64.1.1.7, and the three-way
TCP handshake is established between the client and the Px series application
switch.
• Using its configured load balancing policy, the Px series application switch selects
one of the web servers. In this example, server 1.
• A three-way TCP handshake is established between the Px series application switch
(C) and server 1 (D).
• The application switch forwards the first data request (E) from the client to server 1.
• Server 1 sends a cookie to the client (via the application switch) (F). The cookie
contains unique identifying information for this client session. For example, the
cookie could contain the username:
user=samsmith96754
• Each subsequent request sent from the client to the website contains the cookie.
• The client sends another data request to the website (via the application switch).
• The application switch examines the cookie and performs a mathematical hash
operation on the cookie, rendering a numeric value.
The selected server may or may not be the same server that provided the client
cookie.
• The application switch examines the cookie, performs the same mathematical hash
on the cookie, renders the same numeric value each time, and sends each subsequent
request from this client to server 3.
Learned Cookie Persistence Mode
Using learned cookie persistence, the Px series application switch creates a database
that stores historical information about each session. The database contains the
following information:
• Cookie
• Source IP address
• Destination VIP address
• Real server IP address
The application switch uses the stored information to match the incoming cookie with
the previous connection made by the same client.