Slb Implementation; Distribution Modes; Distribution Algorithms - D-Link DFL-1600 User Manual

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24.2

SLB Implementation

To implement the SLB method, the administrator defines a server farm
containing multiple real servers, and binds the server farm as a single
virtual server to the D-Link firewall (load balancer), using a public IP
address. In this environment, clients are configured to connect to the public
address of the sever farm. When a client initiates a connection to the server
farm, the firewall uses the SAT rule to translate the destination address.
Which real servers will be chosen by the firewall as the most appropriate
ones is determined by predefined mode and algorithm. Cooperating with the
distribution task, the firewall monitors the "health" of the servers through
some layer 3/layer 4 connection checks.
24.2.1

Distribution Modes

D-Link firewalls could be configured to work for SLB with the following
modes:
Per-state Distribution:
The state of every distribution is recorded by the firewall. A complete
session would be transferred to the same server to guarantee reliable
data transmission.
IP Address Stickiness:
Sticky modes track the client connections to provide transmission
integrity. In IP address stickiness mode, within the Idle Timeout
duration, new arriving connections from a client IP address are
assigned to the same real server as were previous connections from
that address. The Idle Timeout in seconds is user-configurable and is
refreshed after the arrival of a new connection.
Network Stickiness:
This mode works as the same as IP address stickiness, just apply to
subnetwork addresses.
24.2.2

Distribution Algorithms

As advanced server load balancers, D-Link firewalls use configurable
algorithms as selection criterion to control the traffic distribution. The
firewall intelligently chooses the most appropriate servers and aims to
maximize the total utilization of the server farm.
Chapter 24. Server Load Balancing (SLB)
D-Link Firewalls User's Guide