Connections From Three Clients; Stickiness And Round-Robin - D-Link NetDefend DFL-210 User Manual

10.3.4. The Distribution Algorithm
Connection Rate
If the Connection Rate algorithm is used without stickiness, it will behave as a Round Robin al-
gorithm that allocates new connections to servers in an orderly fashion. It will also behave as the
Round Robin algorithm if there are always clients with a new IP address that make one connection.
The real benefit is when using Connection Rate together with stickiness and clients make multiple
connections. Connection Rate will then ensure that the distribution of new connections is as even as
possible among servers. Before the interval reaches the specified Idle Timeout of stickiness, new in-
coming connections from the same IP address as a previous connection are assigned to the same
server. The connection with a new address will be redirected to a server with the lowest connection
rate. The algorithm aims to minimize the new connection load for a server, but the distribution may
get uneven if a client from a single IP is sending lots of new connections in a short time and the oth-
er servers do not get as many new connections.
In the management interface, the time window is variable for counting the number of seconds back
in time to summarize the number of new connections for the connection-rate algorithm. As default
value, 10 is used so that the number of new connections which were made to each server in the last
10 seconds will be remembered.
An example is shown in the figure below. In this example, the D-Link Firewall is responsible for
balancing connections from 3 clients with different addresses to 2 servers. Stickiness is set.
Figure 10.6. Connections from Three Clients
When the Round Robin algorithm is used, the first arriving requests R1 and R2 from Client 1 are
both assigned to one sever, say Server 1, according to stickiness. The next request R3 from Client 2
is then routed to Server 2. When R4 from Client 3 arrives, Server 1 gets back its turn again and will
be assigned with R4.
Figure 10.7. Stickiness and Round-Robin
gorithm cycles through the server list and redirects the load to servers in or-
der. Regardless of each server's capability and other aspects, for instance,
the number of existing connections on a server or its response time, all the
available servers take turns in being assigned the next connection.
This algorithm ensures that all servers receive an equal number of requests,
therefore it is most suited to server farms where all servers have an equal
capacity and the processing loads of all requests are likely to be similar.
This algorithm considers the number of requests that each server has re-
ceived over a certain timeframe. SLB sends the next request to the server
that has received the lowest number of connections in that time. The ad-
ministrator is able to specify the timeframe to use with this algorithm.
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Chapter 10. Traffic Management