Extreme Networks Px Series manual Layer 7 Load Balancing and Content Analysis

Client Real Server

SYN

ACK

DATA

(http request)

1

SYN/ACK

WS_013

Figure 1-2:Single client-server transaction using layer 4

As soon as the first request from the client is received at the application switch, the application switch uses the server-selection policy configured for the VIP to select the server and immediately sends out the NAT-ed request to the real server. The client and server continue the connection establishment protocol using the application switch in the middle, NAT-ing the traffic. After the connection is established, an HTTP request is sent and the server responds.

Layer 7 Load Balancing and Content Analysis

To make server-selection decisions based on cookies or the URL being requested by the client, the application switch must actually look inside the client request. Because this data request is only sent out after a connection is established, the Px series application switch must first act as a proxy for the server by acting as the endpoint of the TCP/IP connection from the client. This process is called layer 7 load balancing.

The Px series application switch delays the establishment of a connection to a server until the first 1500 bytes of actual data (the HTTP request) is received from the client. The application switch then takes the content being requested, along with the domain to which the request pertains, and applies policy rules. Based on the outcome of the policy decision, the application switch establishes a TCP connection with the real server

1-4 Px Series Application Switch Installation and Configuration Guide