Session Persistence - Enterasys N Standalone (NSA) Series Configuration Manual

IP Configuration Command Set
Configuring Load Sharing Network Address Translation (LSNAT)
•
The virtual port used by the virtual server (configured with the virtual command,
Section 12.2.8.15) should match the real port used by the real server (configured with the real
command, Section
configuring sticky persistence. (See
page 12-69.)
Choose a port number for an application that is running on the servers. For example, if Telnet is
a service running on the real server, you can configure the real server port number to be 23.

Session Persistence

Load balancing clients connect to a virtual IP address which, in reality, is redirected to one of
several physical servers in a load balancing server farm group. In many web page display
applications, a client may have its requests redirected to and serviced by different servers in the
group. In certain situations, however, it may be critical that all traffic for the client be directed to
the same physical server for the duration of the session—this is the concept of session persistence.
When the router receives a new session request from a client for a specific virtual address, the router
creates a binding between the client (source) IP address/port socket and the (destination) IP
address/port socket of the load balancing server selected for this client. Subsequent packets from
clients are compared to the list of bindings. If there is a match, the packet is sent to the same server
previously selected for this client. If there is not a match, a new binding is created. How the router
determines the binding match for session persistence is configured with the persistence level
command when the virtual server is created.
There are three configurable levels of session persistence:
•
TCP persistence — a binding is determined by the matching the source IP/port address as well
as the virtual destination IP/port address. For example, requests from the client address of
134.141.176.10:1024 to the virtual destination address 207.135.89.16:80 is considered one
session and would be directed to the same load balancing server (for example, the server with IP
address 10.1.1.1). A request from a different source socket from the same client address to the
same virtual destination address would be considered another session and may be directed to a
different load balancing server (for example, the server with IP address 10.1.1.2). This is the
default level of session persistence.
•
SSL persistence — a binding is determined by matching the source IP address and the virtual
destination IP/port address. Note that requests from any source socket with the client IP address
are considered part of the same session. For example, requests from the client IP address of
134.141.176.10:1024 or 134.141.176.10:1025 to the virtual destination address
207.135.89.16:80 would be considered one session and would be directed to the same load
balancing server (for example, the server with IP address 10.1.1.1).
12-68 Matrix NSA Series Configuration Guide
12.2.8.4) in conjunction with the same virtual server, except when
"Sticky Persistence Configuration Considerations" on