ZyXEL Communications ZyWALL 310 - 22.3.5 Virtual Server Load Balancing Algorithms

Chapter 22 Virtual Servers
ZyWALL Series CLI Reference Guide
200
Only certain Zyxel Device models support virtual server load balancing. There are also limits on the
maximum number of rules and real servers per Zyxel Device.
22.3.5 Virtual Server Load Balancing Algorithms
A rule’s load balancing algorithm determines which real server is assigned to an incoming connection
request. When creating a load balancing rule, you can assign each server a weight, which indicates the
server’s processing capacity compared to other servers.
Table 100 Virtual Service Load Balancing Limits
PARAMETER MODEL LIMIT
Maximum Number of Load
Balancing Rules per Zyxel Device
VPN50, USG FLEX 100, USG FLEX
100W, ATP100, ATP100W
5
VPN100, USG FLEX 200, ATP200 10
VPN300, USG FLEX 500, ATP500,
USG FLEX 700, ATP700, ATP800,
VPN1000
20
Maximum Number of Real Servers
Per Load Balancing Rule
All of the above models 4
Table 101 Virtual Server Load Balancing Algorithms
ALGORITHM DESCRIPTION
Round-Robin The Zyxel Device assigns servers in the reverse order they were added to the rule
(Last In First Out). All servers are considered equal, regardless of their weight and
current number of connections.
For example, if you have three servers, A, B, C and nine requests, the servers are
assigned in the following order: CBACBACBA.
Weighted Round-Robin The Zyxel Device assigns servers based on a user-specified weight. Servers with a
higher weight are assigned before servers with a lower weight. Each time a server is
assigned a request, the server’s weight decreases by one point until it finishes
processing the request.
The Zyxel Device assigns servers with equal weight in the reverse order they were
added to the rule (Last In First Out). Servers with zero connections are given priority
over all other servers.
For example, if you have three servers A, B, C with weights 4, 3, 2 and nine requests,
the servers are assigned in the following order: CBAABACBA.
C (Weights: A4, B3, C2)
CB (Weights: A4, B3, C1)
CBA (Weights: A3, B2, C1)
CBAA (Weights: A2, B2, C1)
CBAAB (Weights: A2, B1, C1)
CBAABA (Weights: A1, B1, C1)
CBAABAC (Weights: A1, B1, C0)
CBAABACB (Weights: A1, B0, C0)
CBAABACBA (Weights: A0, B0, C0)