KEMP Technologies LoadMaster 1500 Operator's manual

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Copyright © 2000 - 2005 KEMP Technologies, Inc. All Rights Reserved.
LoadMaster 1500
Installation and Configuration
Guide

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Copyright © 2000 - 2005 KEMP Technologies, Inc. All Rights Reserved.
Copyright © 2000 - 2005 KEMP Technologies, Inc. All rights reserved.
KEMP Technologies, Inc. reserves all ownership rights for the LoadMaster product line including software and
documentation.
The use of the LoadMaster Load Balancer is subject to the license agreement.
Information in this guide may be modified at any time without prior notice.
Company names used in examples are fictitious unless otherwise noted.
Sun, Sun Microsystems, the Sun Logo, Solaris, SunOS and Java are trademarks or registered trademarks of
Sun Microsystems, Inc. in the United States and other countries.
UNIX is a registered trademark of X/Open Company Ltd.
IBM is a registered trademark of International Business Machines Corporation.
Microsoft, Windows and Windows NT are registered trademarks of Microsoft
Corporation.
Linux is a registered trademark of Linus Torvalds.
Intel and Pentium are registered trademarks of Intel Corporation.
All other trademarks and registered trademarks are the property of their respective owners.
Document version: V1.4
Date of issue: 02/11/2005

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TABLE OF CONTENTS
SECTION I. APPLICATION GUIDE ....................................................................................................8
A. Preface........................................................................................................................................8
1. Foreword .................................................................................................................................8
2. The LoadMaster Documentation ..................................................................................................8
3. Typographical Conventions.........................................................................................................8
4. Glossary and Abbreviations ........................................................................................................8
B. Overview of the LoadMaster ........................................................................................................9
1. Load Balancing and it’s Benefits ..................................................................................................9
2. Considerations in Getting Started ..............................................................................................10
3. A Simple Balancer Configuration................................................................................................11
4. LoadMaster Load Balancer Features...........................................................................................12
C. LoadMaster Network Topologies................................................................................................14
1. One-Armed Balancer ...............................................................................................................14
2. Two-Armed and Multi-Armed Balancer .......................................................................................14
3. Direct Server Return – DSR example ..........................................................................................15
D. Miscellaneous Networking Issues ..............................................................................................16
1. S-NAT ...................................................................................................................................16
2. Default Gateway and Routes.....................................................................................................17
E. Single/Dual Unit Configurations ................................................................................................18
1. Single Unit Configuration..........................................................................................................18
2. High Availability (HA) Configuration...........................................................................................18
F. Balancing Methods......................................................................................................................19
1. Round Robin ..........................................................................................................................19
2. Weighted Round Robin.............................................................................................................20
3. Least Connection ....................................................................................................................20
4. Weighted Least Connection.......................................................................................................20
5. Agent Based Adaptive Balancing................................................................................................20
G. Layer 4 Persistency ....................................................................................................................21
1. Source IP Address Based Persistency .........................................................................................21

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H. Layer 7 Persistency ...................................................................................................................21
1. SSL session ID Based Persistency..............................................................................................21
2. URL Based Persistency.............................................................................................................21
3. URL Host Based Persistency......................................................................................................22
4. Cookie Based Persistency.........................................................................................................22
5. Cookie/Source (Cookie or IP source) Based Persistency ................................................................22
6. Active Cookie Based Persistency................................................................................................22
7. Active Cookie/Source (Active Cookie or IP source) Based Persistency..............................................22
8. Cookie hash Persistency...........................................................................................................22
9. Port Following.........................................................................................................................22
I. SSL Acceleration .......................................................................................................................23
1. Certificate files .......................................................................................................................23
J. Rule Based Content Switching....................................................................................................23
1. Rule Definition........................................................................................................................23
1.1. Special Characters................................................................................................................24
1.2. Regular expressions..............................................................................................................24
1.3. Host name matching.............................................................................................................24
K. Health Checking ........................................................................................................................25
1. Service and non-service based Health Checking...........................................................................25
L. SNMP Support............................................................................................................................27
1. LoadMaster Performance Metrics via SNMP .................................................................................27
2. LoadMaster Event Traps via SNMP.............................................................................................28
M. LoadMaster Software Upgrades ................................................................................................29
1. Online Upgrades .....................................................................................................................29
N. Miscellaneous.............................................................................................................................29
1. Remote Syslogd Support..........................................................................................................29
2. How to get a license................................................................................................................30
2.1. Get a 30 day evaluation license..............................................................................................30
2.2. Get a full LoadMaster license..................................................................................................30
2.3. Get full High Availability LoadMaster cluster licenses..................................................................30
2.4. Upgrading the evaluation license to a full single or HA license......................................................31
3. Backup and Restore ................................................................................................................31
4. System recovery.....................................................................................................................31
5. Interoperability between L4 / L7 Virtual Services .........................................................................32
O. Appendix I.................................................................................................................................32

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1. API for Agent Based Adaptive Balancing .....................................................................................32
2. Http Server Configuration for Cookie Support..............................................................................33
3. MIB-tree................................................................................................................................34
II. INSTALLATION AND CONFIGURATION GUIDE ..........................................................................34
A. Before Getting Started...............................................................................................................34
1. The LoadMaster Appliance........................................................................................................35
1.1. Delivery Content ..................................................................................................................35
1.2. LoadMaster 1500 Hardware ...................................................................................................35
2. Connecting the Hardware.........................................................................................................35
B. Initial Setup of your LoadMaster Single Unit (non-HA)..............................................................35
1. Login and License Key .............................................................................................................35
C. Initial Setup of a LoadMaster High Availability (HA) Cluster......................................................36
1. Login and License Key .............................................................................................................36
2. Configuring the second LoadMaster............................................................................................36
D. Quick Setup................................................................................................................................37
E. Main Menu ..................................................................................................................................38
1. Configuration Menu basics........................................................................................................38
1.1. Quick Setup.........................................................................................................................39
2. Service Management (CLI) .......................................................................................................39
3. Local Administration................................................................................................................39
3.1. Set Password.......................................................................................................................39
3.2. Set Date/Time .....................................................................................................................39
3.3. Set Keyboard Map.................................................................................................................39
3.4. Backup/Restore ...................................................................................................................40
3.5. Remote Access Control..........................................................................................................40
4. Basic Setup............................................................................................................................40
4.1. Network configuration...........................................................................................................40
4.2. Hostname Configuration........................................................................................................41
4.3. DNS configuration ................................................................................................................41
5. Extended Configuration............................................................................................................41
5.1. Interface Control..................................................................................................................41
5.2. Enable/Disable S-NAT ...........................................................................................................41
5.3. Syslogd Configuration...........................................................................................................42
5.4. SNMP metrics ......................................................................................................................42
5.5. SNMP traps .........................................................................................................................42

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5.6. Enable/Disable L7 persistency state failover .............................................................................43
5.7. Enable/Disable L4 connection state failover..............................................................................43
5.8. Multicast Configuration..........................................................................................................43
5.9. HA timeout..........................................................................................................................43
6. Packet Filter & Access Control Lists.............................................................................................43
6.1. Access control Lists ..............................................................................................................43
7. Utilities..................................................................................................................................44
7.1. Software Upgrade ................................................................................................................44
7.2. Transfer mode .....................................................................................................................44
7.3. Network Time Protocol Host...................................................................................................45
7.4. SSL certificate administration.................................................................................................45
7.5. Update License ....................................................................................................................45
7.6. Diagnostics .........................................................................................................................45
8. Reboot ..................................................................................................................................46
9. Exit LoadMaster Config ............................................................................................................46
F. The LoadMaster Questionnaire ...................................................................................................46
1. Single LoadMaster Balancer Solution..........................................................................................46
2. Highly Available dual LoadMaster Balancer Solution......................................................................46
III. COMMAND LINE INTERFACE...................................................................................................47
2. Adaptive scheduling command level...........................................................................................48
3. Health check command level.....................................................................................................49
5. Rule Edit command level..........................................................................................................50
6. Virtual Service (VIP) command level..........................................................................................51
IV. WEB USER INTERFACE (WUI) CONFIGURATION GUIDE ...........................................................56
A. Glossary and Abbreviations .......................................................................................................56
B. Fast Track..................................................................................................................................57
1. How To Login .........................................................................................................................57
2. Create a Simple Virtual Service.................................................................................................57
3. Create a Virtual Service with Content Rules ................................................................................60
4. Create an SSL accelerated Virtual Service...................................................................................63
C. Full Menu Tree...........................................................................................................................64
1. Home....................................................................................................................................65
2. Virtual Services ......................................................................................................................65
2.1. Add Virtual Service...............................................................................................................65
2.2. Virtual Service Properties ......................................................................................................65

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2.3. Real Server Assignment ........................................................................................................67
2.4. Add / Modify Real Server.......................................................................................................67
2.5. Add Rule.............................................................................................................................68
2.6. Rule Precedence...................................................................................................................68
3. Global Settings.......................................................................................................................68
3.1. Content Rule Management.....................................................................................................68
3.2. Service Health Check Parameters ...........................................................................................68
3.2.1. Check Interval ..................................................................................................................68
3.3. Connect & Response timeouts................................................................................................69
3.4. Re-try Count .......................................................................................................................69
4. Adaptive Parameters ...............................................................................................................69
4.1. Adaptive Interval .................................................................................................................69
4.2. Adaptive URL.......................................................................................................................69
4.3. Port.....................................................................................................................................69
4.4. Min Control Variable Value.....................................................................................................69
4.5. Min Weight Adjustment Value.................................................................................................69
4.6. Real Server Availability .........................................................................................................69
5. Balancer Metrics .....................................................................................................................70
5.1. Global Metrics......................................................................................................................70
5.1.2. Real Server Metrics............................................................................................................70
5.1.3. Virtual Service Metrics........................................................................................................70
6. System Properties...................................................................................................................70
6.1. Route Management...............................................................................................................70
6.2. Access Control.....................................................................................................................70
6.2.1. Packet Filter Enabled..........................................................................................................70
6.2.2. Reject/Drop blocked packets ...............................................................................................71
6.2.3. Access control Lists............................................................................................................71
6.2.4. Add Address .....................................................................................................................71
6.3. Miscellaneous ......................................................................................................................71
6.3.1. SNAT Control....................................................................................................................71
6.3.2. Set Transfer Protocol..........................................................................................................71
6.3.3. Set HA Timeout.................................................................................................................71

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Copyright © 2000 - 2005 KEMP Technologies, Inc. All Rights Reserved.
Section I. Application Guide
A. Preface
1. Foreword
Thank you for purchasing KEMP’s LoadMaster!
We wish you much success with your KEMP’s LoadMaster Appliance.
2. The LoadMaster Documentation
The KEMP’s LoadMaster documentation consists of 2 manuals:
- The Application and Installation guide, which describes the main features of the
Load Balancer and the setup of the LoadMaster hardware component,
- The WUI manual, i.e. the manual for the Web User Interface, which describes the setup and control of a
Load Balancing Site via the Web User Interface.
3. Typographical Conventions
Screenshots and photographs may be design models and might not correspond exactly to real-life
components.
4. Glossary and Abbreviations
Access Code: An Access Code will be generated during the initial setup of the LoadMaster. You must contact
your KEMP Technologies representative for your 60-day evaluation or your full purchased license key.
Balancer: A network device or logic that distributes inbound connections with a common source address
across a farm of server machines.
Farm Side: The LoadMaster network interface to which the server farm is connected.
Flat-based: The VIPs and the real servers are on the same subnet.
HA: Highly Available or High Availability (used interchangeably)
ICMP: Internet Control Message Protocol
MIB: Management Information Base, a database of object definitions. The definition specifies whether an
SNMP manager can monitor the object.
NAT: Network Address Translation
NAT-based: The VIPs and the real servers are on different subnets.
Network Side: The LoadMaster network interface over which requests to the server farm are made.
One-armed: Only one Ethernet interface is used for in and outbound traffic. Farm side and Network side are
both connected to it.
RS: Real Server: Physical server machines which make up a server farm.
Service: A Service is an application that is connected to the network.
Shared IP: The shared (floating) IP address is always the assigned IP address of the active LoadMaster in a
HA solution.

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SCP: Secure copy command of SSH
SNMP: Simple Network Management Protocol, a network protocol used to manage TCP/IP networks. This
protocol provides functions that enable you to access the data object whose definitions are located in the MIB.
S-NAT: Network Address Translation for a source IP address.
SSH: Secure Shell Protocol
Two-armed: Two Ethernet interfaces are used for in and outbound traffic, one connected to the network side
and one to the farm side.
UTC: Universal Time Coordinated
VIP: Virtual IP Address: The IP address of a service defined on the LoadMaster.
VS: Virtual Service: An entry on the LoadMaster over which a service being hosted in the server farm can be
reached.
WUI: Web User Interface used to perform LoadMaster administration via a web browser.
B. Overview of the LoadMaster
1. Load Balancing and it’s Benefits
As the Internet and networking based Applications evolve and become more sophisticated, they also become
more complicated and unwieldy for those who operate these services and applications. Consequently, the
following issues become key in providing users with the Quality of Service they expect and require:
 Scalability of server machines – as the demand on services and applications grows, it is no longer
sufficient to simply upgrade the hardware that hosts these units. Sooner or later, physical limits of
hardware upgradeability are reached. Furthermore, users are not willing to accept the downtime that
accompanies such upgrades.
 High availability of services and applications – as Internet based networking is used for mission critical
applications such as banking, B2B and voice over IP, the availability of services can easily determine
the success or failure of a business.
 Greater flexibility – as the number and diversity of Internet services and applications increases, it
becomes imperative for network managers to have an environment in which they can trivially “juggle”
their resources around on demand, without endangering the robustness of the environment.
 Improved performance – mission critical services and applications require deterministic response
times. The competition is only a click away.
The Solution . . .
Load Balancers are highly robust network devices, and have the effect of making several server machines
appear as one. Thus, a network service can be distributed across an array of physical machines – sometimes
referred to as a server or application farm. The Load Balancer channels requests to a network service using a
variety of intelligent scheduling methods. This has several benefits, which is why load balancing has become a
successful and widely employed technique in recent years:
 Scalability of server machines – can be achieved by simply adding server machines to the farm as
demand for services increases. Upfront investments in server capacity, which may go unused, can be
avoided.

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 High availability of services and applications – since services are replicated across multiple machines
within the farm, the loss of a single server does not result in a total loss of service for the customer –
worst case, a drop in performance may be experienced.
 Greater flexibility – server machines can be added and removed from the farm on demand resulting in
an immediate effect. Services – sometimes referred to as Virtual Services in the context of Load
Balancers – can be trivially tuned and shuffled around the server farm, thus ensuring optimal usage of
resources.
 Improved performance – intelligent load balancing algorithms ensure that requests are directed to
those machines in the server farm that can most effectively handle them.
The LoadMaster Load Balancer provides a more reliable, flexible and cost effective solution to addressing high
traffic load and mission critical applications, resulting in a high Quality of Service (QoS) at a low Total Cost of
Ownership (TCO).
2. Considerations in Getting Started
Skip this section if you are already familiar with the basic Load Balancer functions and know how to set up a
Balancer-Server combination.
The Installation and Configuration Guide describes how to go about installing and configuring your LoadMaster
such that load-balanced services (virtual services) can be supported. However, before doing so, the following
considerations covered by the LoadMaster documentation should be taken into account when setting up your
LoadMaster for the first time:
What sort of LoadMaster network topology best suits my application? [See section C of this guide]
Do my real servers require publicly routable IP addresses or can they be “hidden” behind the LoadMaster on a
private network segment? [See section C of this guide]
Does my Application require the Balancer and Real Servers to be part of a flat-based topology? [See section C
of this guide]
Will network connections be initiated from within the application farm to the outside, as well as from the
outside to within the farm? [See section D of this guide]
Do I require a High Availability support in the form of an active/hot-standby redundant cluster? [See section E
of this guide]
How do I intend to replicate my application across multiple real server machines?
What kind of Virtual Service settings best suits my application? [See section F of this guide]
Will a round robin balancing algorithm do or do I need to take aspects of my application into consideration and
report these back to the Balancer? [See section F of this guide]
Is connection persistency at all an issue for my application? [See section G and H of this guide]
Will source-based IP persistency suffice or do I need to take layer 7 aspects into consideration? [See section G
and H of this guide]
Do I wish to integrate the LoadMaster into my current SNMP environment? [See section
J of this guide]
Which forms of real server health checking will best suite my application? [See section K of this guide]

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Do I prefer a Command Line Interface for provisioning my Virtual Services or do I require the use of the Web
based interface? [Refer to the Command Line Reference Guide Section III, and the WUI Handbook]
Do I wish the LoadMaster event logs to be reported to a central Syslogd? [See section N of this guide]
Do I require remote access to the CLI? [See section E of the Installation and Configuration Guide]
Do I wish to allow my balancer to be accessed by KEMP Technologies for maintenance purposes? [See section
E of the Installation and Configuration Guide]
3. A Simple Balancer Configuration
Taking the above issues into consideration, an example Load Balanced Site may look as follows:
Figure 1: Example of a simple Balancer configuration
A Virtual Service (VS) has been created on the LoadMaster with IP address 66.220.13.66 for an http service.
This Virtual Service has been configured to balance the incoming traffic across real servers (RS) server 1,
server 2 and server 3.

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A client requests "http://www.kemptechnologies.com".
The URL will be resolved into 66.220.13.66.
The request will be routed to the LoadMaster, which offers this IP address as an IP-alias of its network
interface eth0.
The LoadMaster is connected to the server farm subnet 10.0.0.0 via its network interface eth1.
The LoadMaster knows that in this subnet were three Real Servers assigned to the requested address
66.220.13.66 and able to deliver the required content.
The LoadMaster uses the load balancing method you configured - e.g. weighted round robin - and distributes
the request onto one of the three Real Servers.
4. LoadMaster Load Balancer Features
The LoadMaster load balancer provides the following features with the Balancer Operating Software and the
Web User Interface:
The Balancer Operating Software Basics
 Server Load Balancing (SLB) for TCP/UDP based protocols
 Multi-armed Balancer/Server Farm network topology with NAT-based forwarding. See note 1.
 Compact Flash bootable Operating Software
 S-NAT support for multi-armed solutions. See note 2.
 One and two-armed flat-based 3 Balancer/Server Farm topologies
 Support of Direct Server Return (DSR) configurations
 Optional force setting of duplex mode for Balancer Ethernet interfaces
 Option to allow remote access to Balancer for maintenance purposes
 VLAN tagging support
NOTES:
1. Real Servers and the Virtual Services are maintained in different logical networks using a NAT-like
forwarding mechanism. For this purpose the LoadMaster uses two Ethernet interfaces (hence two armed).
2. If S-NAT is enabled, then connections initiated from a Real Server to the Internet assume the source IP
address of the balancer.
3. A flat-based topology is one in which the Real Servers and the Virtual Services are part of the same logical
network.
4. Full duplex mode.
5. A performance benchmark report is available from KEMP Technologies.
Scheduling and L4 / L7 Persistency
 Four static load-balancing methods
 Agent based automatic adaptive balancing with real server API
 Connection persistency based on:
- Source IP address

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- SSL Session ID
- URL
- Host Header
- Passive Cookie
- Active Cookie (Insert)
- Cookie Hash
- Cookie Hash Source
- Query Hash
 Port following for persistency options
 SSL acceleration
Health Check and Availability
 ICMP health checking of server farm machines
 Service checking for DNS, FTP, HTTP, HTTPS, IMAP, NNTP, POP3, SMTP, TELNET
 Automatic reconfiguration of defective real server machines
 Active/Hot-Standby configurations for High Availability as an option
 Stateful Failover of Cookies and TCP connections
Administration
 Web based interface for creation, deletion and editing of Virtual Services
 Command Line Interface (CLI) for the creation, deletion and editing of Virtual Services
 Packet filtering functionality
 Remote Syslogd support
 Remote access to the LoadMaster for all administrative Balancer operations
 Selective restore of Balancer and Virtual Service data
 Online software upgrades for LoadMaster Operating Software
 SNMP support for event traps
 SNMP for performance metrics
Miscellaneous
 Support of Time Zones
 Change password function for administrative login “bal”
 Password recovery mechanism for login “bal”
 Multi-language keyboard support

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C. LoadMaster Network Topologies
1. One-Armed Balancer
If a one-armed configuration is selected then the following is true:
 Only the eth0 Ethernet interface will be used (for both in and outbound traffic)
 Real Servers and Virtual Services will be part of the same logical network – sometimes called flat-
based - this implies that both have public IP addresses if used for services within the Internet.
 S-NAT does not make sense for one-armed configurations.
 Does not automatically imply the use of Direct Server Return (DSR) methods on the Real Servers
 Implies the clients (consumers of the service hosted by the LoadMaster) are on a logically separate
network to the LoadMaster and its’ Virtual Services (this is not true if used in conjunction with DSR).
2. Two-Armed and Multi-Armed Balancer
If a two-armed or Multi-Armed configuration is selected, then the following is true:
 Both eth0 (net side) and eth1 (farm side) interfaces are used. Additional ports go to the farm side for
Multi-Armed configurations
 Implies that the LoadMaster (eth0) and server farm(s) are on separate logical networks, sometimes
referred to as a NAT based topology.
 The server farm(s) may make use of non-routable IP addresses
 S-NAT may be useful in such a configuration
 Clients may be on the same logical network as the LoadMaster

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 Virtual Services may be created on either eth0 or eth1. Up to eth7 on Multi-Armed configurations
 Real Servers may exist on either the eth0 or up to the eth5 network. However, placing Real Server on
eth0 in a two-armed configuration is not recommended.
3. Direct Server Return – DSR example
1 – incoming request intercepted by LoadMaster
2 – routed to Test Server 1
3 – response from Test Server 1
4 – Response goes directly to Client without LoadMaster

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Figure above: Sample Direct Server Return configuration
This feature should be implemented only if the real servers need to respond to the clients directly, without
going through the LoadMaster. In this configuration the real servers should have a path to the clients without
going through the balancer, i.e. additional routes bypassing the LoadMaster.
Note: This mode is only available when not using any persistency options.
DSR uses a combination of MAT (MAC address translation) and a special RS configuration. The RS is
configured with an IP address as normal but it is also given the IP address of the VIP. Normally you cannot
have two machines on a network with the same IP address. To get around this, the VIP address on the Real
Server should be configured so that they do not respond to arp requests. For Linux with a recent 2.4 kernel,
this can be done by creating the VIP as an IP alias on the loopback interface.
When you create the VS and assign the respective real servers to it, select “route” as the forwarding method
to the real servers. This means that the balancer just routes the packets from a client to a RS without
modifying the IP addresses. The real server accepts requests for the VIP destination address because it has
configured the VIP as an IP alias. The real server will then reply to the IP address of the requesting client with
the source IP address of the reply set to the VIP.
Step Source IP Destination IP MAC Address
1 216.139.43.10 195.30.70.200 Dest: 00:00:00:00:00:aa
2 216.139.43.10 195.30.70.200 Dest: 00:00:00:00:00:bb
3 195.30.70.200 216.139.43.10 Source: 00:00:00:00:00:bb
Configuring a VIP on the loopback interface on Linux
On a linux machine the “ifconfig –a” command will look something like this:
root@RS1 $ ifconfig –a
eth0 Link encap:Ethernet HWaddr 00:00:00:00:00:bb inet addr: 195.30.70.11 Bcast: 195.30.70.255
Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:96561817
errors:526 dropped:0 overruns:5 frame:0 TX packets:97174301 errors:0 dropped:0 overruns:0
carrier:0 collisions:0 txqueuelen:100 Interrupt:10 Base address:0x4000
lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 UP LOOPBACK RUNNING MTU:3924
Metric:1 RX packets:3985923 errors:0 dropped:0 overruns:0 frame:0 TX packets:3985923 errors:0
dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0
To create an additional loopback interface with an IP alias use the “ifconfig” command like this:
root@RS1 $ ifconfig lo:1 195.30.70.200 broadcast 195.30.70.200 \ netmask 255.255.255.255
root@RS1 $ ifconfig lo:1
lo:1 Link encap:Local Loopback inet addr:195.30.70.200 Mask:255.255.255.255 UP LOOPBACK RUNNING
MTU:3924 Metric:1
D. Miscellaneous Networking Issues
1. S-NAT
When using a two-armed or multi-armed balancer configuration, it is sometimes useful for the real servers to
have access to the Internet. The default route for the real servers is through the balancer. If however the real
servers do not have routable addresses i.e. private addresses, this is not possible.
Using S-NAT, the balancer will map all connections originating on a real server so that they appear to come
from the balancer itself. The real servers can thus use the Internet as if directly connected but with the extra
security protection that they cannot be addressed directly from the Internet.

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The use of S-NAT in single-armed configurations is not recommended.
The S-NAT functionality may be disabled over the configuration menus and WUI.
2. Default Gateway and Routes
In simple configurations, where the LoadMaster is installed in a network where there is only one route to the
Internet, only the default gateway needs be specified. All traffic from the LoadMaster to the Internet will then
be routed over this gateway. An example configuration is given in figure A.
When the LoadMaster is installed in a more complicated network configuration (for example as depicted in
figure B), the default gateway must still be specified but will only be used if additional routes are not
available. Additional routes may be specified so that traffic for the specified addresses will be routed over
alternative gateways. For example in figure B, a route could be set up to route data from a private network or
over a secondary link gateway.
Only static routes can be set up on the LoadMaster (see the Installation and Configuration Guide in this
handbook). The balancer does not currently support external routing protocols.
Figure A. Figure B.

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E. Single/Dual Unit Configurations
1. Single Unit Configuration
The topology in standalone-mode looks like this:
2. High Availability (HA) Configuration
The High Availability feature of the LoadMaster guarantees the availability of your server farm. HA is achieved
by a hot-standby, failover mechanism. Two identical LoadMaster units are integrated into your network. One
machine serves as the active balancer, the second one remains in a standby, idle state, always prepared to
take over the activities from the active server. This two-machine cluster appears both to the Internet side and
to the server farm side as a single logical unit.
Note: If you are running a High Availability (HA) cluster, which consists of two interconnected LoadMaster
nodes, each network interface has an individual IP address and a shared (sometimes called floating) IP
address. The shared IP address is identical for both LoadMaster nodes, but active only for one LoadMaster at
any one time.
During normal operation each node is periodically sending health check messages over the two connections to
cross check the operability of the peer machine. In the unlikely event that a LoadMaster should fail, the
standby machine will become active and take over the task of balancing.

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The topology in high availability-mode looks like this:
Note: In HA mode, the Real Servers must have the shared IP address of the LoadMaster farm-side interface
configured as the default gateway.
F. Balancing Methods
There are several load balancing methods provided by the LoadMaster, which are known as "scheduling rules"
or “algorithms”:
1. Round Robin
With this method incoming requests are distributed sequentially across the server farm (cluster), i.e. the
available servers.
If this method is selected, all the servers assigned to a virtual service should have the similar resource
capacity and host identical applications. Choose round robin if all servers have the same or similar
performance and are running the same load. Subject to this precondition, the round robin system is a simple
and effective method of distribution.
However, if the servers have different capacities, the use of the round robin system can mean that a less
powerful server receives the next inquiry even though it has not yet been able to process the current one.
This could cause a weaker server to become overloaded.

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2. Weighted Round Robin
This method balances out the weakness of the simple round robin: Incoming requests are distributed across
the cluster in a sequential manner, while taking account of a static “weighting” that can be pre-assigned per
server.
The administrator simply defines the capacities of the servers available by weighting the servers. The most
efficient server A, for example, is given the weighting 100, whilst a much less powerful server B is weighted at
50. This means that Server A would always receive two consecutive requests before Server B receives its first
one, and so on.
3. Least Connection
Both round robin methods do not take into account that the system does not recognize how many connections
are maintained over a given time. It could therefore happen that Server B is overloaded, although it receives
fewer connections than Server A, because the users of this server maintain their connections longer. This
means that the connections, and thus the load for the server, accumulate.
This potential problem can be avoided with the "least connections" method: Requests are distributed on the
basis of the connections that every server is currently maintaining. The server in the cluster with the least
number of active connections automatically receives the next request. Basically, the same principle applies
here as for the simple round robin: The servers related to a virtual service should ideally have the similar
resource capacities.
4. Weighted Least Connection
If the servers have different resource capacities the “weighted least connection” method is more applicable:
The number of active connections combined with the various weights defined by the administrator generally
provides a very balanced utilization of the servers, as it employs the advantages of both worlds.
This is, in general, a very fair distribution method, as it uses the ratio of the number of connections and the
weight of a server. The server in the cluster with the lowest ratio automatically receives the next request.
5. Agent Based Adaptive Balancing
In addition to the methods above the LoadMaster contains an adaptive logic, which checks the state of the
servers at regular intervals and independently of the configured weighting.
For the extremely powerful “agent based adaptive balancing” method the balancer periodically checks the
system load on all the servers in the farm: Each server machine should provide a file that contains a numeric
value in the range between 0 and 100 representing the actual load on this server (0 = idle, 100 = overload).
The balancer retrieves this file by an HTTP GET operation. It is the server’s job to provide the actual load in
the ASCII file. There are no prerequisites, though, how the servers evaluate this information.
Two different strategies are applied, depending on the overall load of the server farm:
During normal operation the scheduling algorithm calculates a weighting ratio out of the collected load values
and distributes the connections according to it. So if excessive overloading of a server occurs, the weighting is
readjusted transparently by the system. As with the weighted round robin, incorrect distribution can then be
countered by assigning different weights to the servers available.
During a period of very low traffic, however, the load values as reported by the servers will not build a
representative sample. A load distribution based on these values would result in uncontrolled, oscillating
directives. Therefore in such a situation it is more reasonable, to calculate the load distribution based on the
static weight ratio. The balancer switches to the weighted round robin method automatically when the load on
all servers falls below a limit defined by the administrator. If the load rises above the limit the balancer
switches back to the adaptive method.
(See also section O.1: API for Agent Based Adaptive Balancing)