Module 8: Concepts of A Network Load Balancing Cluster v
Module Strategy
Use the following strategy to present this module:
Network Load Balancing Concepts
This topic is an overview of Network Load Balancing concepts.
• Discuss the various clustering technologies and how they compare to
Network Load Balancing.
• Briefly review the features of Network Load Balancing.
• Emphasize that there is no single point of failure with Network Load
Balancing.
• Compare other load balancing solutions to Network Load Balancing by
using the graphic.
• Demonstrate the operations of a Network Load Balancing cluster by
using the graphic.
• Demonstrate the concepts of balancing client connections by using the
graphic.
• Carefully explain the concept of high availability by using the graphic.
Application and Service Environment
• Identify the applications and services environment and discuss the two
kinds of client state and how they are managed.
Network Load Balancing Functionality
• Emphasize how the Network Load Balancing driver balances client
connections and supports multiple client connections by using the
graphics.
• Discuss the concept of cluster convergence.
• Explain the dynamics of high availability within a Network Load
Balancing cluster by using the graphic.
• Explain the scalability concepts within a Network Load Balancing
cluster by using the graphics.
Network Load Balancing Architecture
• Demonstrate the logical position of the Network Load Balancing driver
within the Transmission Control Protocol/Internet Protocol (TCP/IP)
stack by using the graphic.
• Emphasize the importance of properly configuring the Network Load
Balancing driver and selecting the appropriate IP transmission modes.
• Ensure that the students understand the unicast and multicast modes.
• Emphasize the importance of setting consistent port rules for the
Network Load Balancing cluster hosts.
• Discuss the distribution of the incoming client connections based on
affinity.
Module 8: Concepts of A Network Load Balancing Cluster 1
Overview
Network Load Balancing Concepts
Application and Service Environment
Network Load Balancing Functionality
Network Load Balancing Architecture
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Microsoft
® Windows® 2000 Advanced Server and Microsoft Windows 2000
Datacenter Server operating systems include two clustering technologies;
Cluster service and Network Load Balancing service.
Cluster service is intended primarily to provide failover support for critical line-
of-business applications, such as databases, messaging systems, and file/print
services. Network Load Balancing service balances incoming Internet Protocol
(IP) traffic among multihost clusters. This module will address Network Load
Balancing service in detail.
After completing this module, you will be able to:
Describe the concepts of the Network Load Balancing solution.
Describe the application and services configuration for Network Load
Balancing hosts.
Describe the functionality of the Network Load Balancing driver.
Identify the components for the Network Load Balancing driver
architecture.
Topic Objective
To provide an overview of
the module topics and
objectives.
Lead-in
In this module, you will learn
about the features and
functions for Microsoft
Windows 2000 Network
Load Balancing service and
how you can use a
clustering solution to
improve availability,
scalability, and load
balancing.
2 Module 8: Concepts of A Network Load Balancing Cluster
Network Load Balancing Concepts
Comparing Network Load Balancing Solutions
Network Load Balancing
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Internet server programs supporting mission-critical applications and services,
such as financial transactions, database access, corporate intranets, and other
key functions must run 24 hours a days, seven days a week. In addition,
network applications and servers need the ability to scale performance to handle
large volumes of client requests without creating unwanted delays.
Network load balanced clusters enable you to manage a group of independent
servers as a single system for higher availability, easier manageability, and
greater scalability.
You can use Network Load Balancing service to implement enterprise-wide
highly available and scalable solutions for the delivery of Transmission Control
Protocol/Internet Protocol (TCP/IP) based services and applications.
Network Load Balancing has many advantages over other load balancing
solutions that can introduce single points of failure or performance bottlenecks.
Because there are no special hardware requirements for Network Load
Balancing service, you can use any industry standard compatible computer in a
Network Load Balancing cluster.
The Network Load Balancing driver requires that TCP/IP be
installed and supports only Ethernet or Gigabit Ethernet network adapters.
Network Load Balancing does not support network basic input/output system
(NetBIOS) Enhanced User Interface (NetBEUI) or Internetwork Packet
Exchange (IPX).
Topic Objective
To give an overview of
Network Load Balancing
concepts.
Lead-in
Internet server programs
supporting mission-critical
applications and services,
such as financial
transactions, database
access, corporate intranets,
and other key functions,
must run 24 hours a day,
seven days a week.
Delivery Tip
Before leaving this page,
ask the students what load
balancing solutions they
have implemented.
Emphasize to the students
that there are no single
points of failure with
Network Load Balancing.
Im
p
ortan
t
Module 8: Concepts of A Network Load Balancing Cluster 3
Comparing Network Load Balancing Solutions
Round robin DNS
Round robin DNS
Round robin DNS
Easy to
Install
Easy to
Install
Yes
Yes
Hardware
Requirements
Hardware
Requirements
____
____
Single Point
of Failure
Single Point
of Failure
____
____
Easily
Scalable
Easily
Scalable
Yes
Yes
High
Performance
High
Performance
Yes
Yes
Hardware
Hardware
Hardware
____
____
Yes
Yes
Yes
Yes
____
____
Yes
Yes
Dispatch
Dispatch
Dispatch
____
____
____
____
Yes
Yes
Limited
Limited
Limited
Limited
NLB
NLB
NLB
Yes
Yes
____
____
____
____
Yes
Yes
Yes
Yes
Fault
Tolerance
Fault
Tolerance
No
No
Limited
Limited
Limited
Limited
Yes
Yes
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Comparing load balancing solutions will enable you to determine the
advantages and disadvantages of each and to implement a solution that will
provide ease of installation, avoid specialized hardware, and avoid single points
of failure.
Network Load Balancing service is a high performance and cost-effective
solution for both load balancing and fault tolerance where services and
applications use Windows 2000-based computers.
However, selection of a viable solution for your enterprise can depend on many
factors, including the operating system in use, current network hardware, and
network types.
Load balanced clients are able to access a pool of servers with other load
balancing solutions, such as round robin DNS, hardware-based load balancing
and dispatcher software load balancing.
Round Robin DNS
Round robin DNS is a common solution for enabling a limited, static form of
TCP/IP load balancing for Internet server farms.
Consider the following example in which there are three IP address entries for
the same host name on a DNS server.
MyRRDNSWeb IN A 172.17.21.31
MyRRDNSWeb IN A 172.17.21.35
MyRRDNSWeb IN A 172.17.28.41
Topic Objective
To compare load balancing
solutions.
Lead-in
Comparing load-balancing
solutions will enable you to
determine the advantages
and disadvantages of each
and to implement a solution
that will provide ease of
installation, avoid
specialized hardware, and
single points of failure.
Delivery Tip
This topic is an overview of
alternatives to Network Load
Balancing, review each of
the technologies and point
out the benefits of Network
Load Balancing.
Key Point
The table illustrates that the
alternative solutions to
Network Load Balancing
have limitations in some
categories. These limitations
are due to the single point of
failure, packet translation,
and limited communication
between the hosts in a
cluster when implementing
these solutions.
4 Module 8: Concepts of A Network Load Balancing Cluster
Using the previous list of round robin DNS IP address entries, when a client
sends a query, the DNS server returns all three IP addresses to the DNS client,
but typically the client uses only the first one in the list. The next time the DNS
server receives a query for this host the order of the list is changed in a cyclic
permutation or round-robin, meaning that the address that was first in the
previous list is now last in the new list. So if a client chooses the first IP address
in the list, it now connects to a different server. In the event of a server failure,
round robin DNS will continue to route requests to the failed server until you
manually remove the SRV (service) resource record from DNS.
Hardware-Based Load Balancing
Hardware-based load balancing directs client requests for a single IP address to
multiple hosts within a cluster. Hardware load balancers typically use a
technique called network address translation (NAT), which exposes one or
more virtual IP address to clients and forwards data for the designated hosts by
translating IP addresses and resending network packets. This technique
introduces a single point of failure, the computer performing the redirection of
packets, between the cluster and the clients. To achieve high availability with
this solution, you need a backup load balancer.
Dispatcher Software Load Balancing
This load balancing solution requires one dispatch server to handle all incoming
connection requests, where they are then retransmitted to other servers in the
network. This solution limits throughput and restricts performance because the
entire cluster’s throughput is limited by the speed and processing power of the
dispatch server. The single dispatch server represents a single point of failure,
which must be eliminated by moving the dispatching function to a second
computer after a failure occurs.
Network Load Balancing
Network load balancing is a fully distributed, software-based solution and does
not require any specialized hardware or network components. Network load
balancing does not require a centralized dispatcher because all hosts receive
inbound packets, and redundancy is provided according to the number of hosts
within the cluster.
The filtering algorithm for network load balancing is much more efficient in its
packet handling than centralized load balancing programs, which must modify
and retransmit packets. Network load balancing provides a much higher
aggregate bandwidth on similar network configurations.
The slide shows that alternative solutions to network load balancing have
limitations in some categories. These limitations are due to the single point of
failure, packet translation, and limited communication between the hosts in a
cluster.
Note
Module 8: Concepts of A Network Load Balancing Cluster 5
Network Load Balancing
Cluster with up to
32 hosts
Cluster with up to
32 hosts
Round Robin DNS
Static group
Round Robin DNS
Static group
MyRRDNSWeb IN A 10.10.10.12
MyRRDNSWeb IN A 10.10.10.11
MyRRDNSWeb IN A 10.10.10.10
MyNLBWeb IN A 10.10.20.10
10.10.10.12
10.10.20.11
10.10.20.10
10.10.20.10
1
1
2
2
3
3
5
5
DNS Server
DNS Server
6
6
4
4
IP: 10.10.10.12
IP: 10.10.10.12
IP: 10.10.10.11
IP: 10.10.10.11
IP: 10.10.10.10
IP: 10.10.10.10
IP: 10.10.20.10
IP: 10.10.20.10
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Many enterprise solutions must address client access to services and
applications that are based on connections to selected TCP/IP addresses,
protocols, and port numbers. For example, Internet Information Services (IIS)
provides service to clients on IP (TCP, 80). If this single IP host were to fail or
become overloaded, client access to the service or application may be prevented
or fall below a designated performance level.
Configuring multiple hosts to increase availability, scalability, and fault
tolerance for applications and services is one solution. However, this solution
may involve specialized network hardware, complex network configuration,
and management of individual hosts. For example, multiple hosts functioning as
Web servers, each with an individual IP address, could be resolved by multiple
entries in round robin DNS. As shown in the graphic where the arrows 1, 2, 3
represent a client Uniform Resource Locator (URL) query, DNS response and
cluster connection request. Each server is independent and should a server fail,
the static load balancing provided by round robin DNS may prevent clients
from accessing their Web application.
To resolve client connection problems, Windows 2000 Network Load
Balancing service allows multiple computers or hosts, configured in a logical
group called a network load balancing cluster, to respond to client connection
requests made to a single virtual IP address. For example, as shown in the
graphic, arrows 4, 5, 6 represent a client URL query, DNS response, and a
cluster connection request. You will notice that only one IP address is supplied
to the client.
Topic Objective
To introduce the
configuration performance
and management features
of Network Load Balancing.
Lead-in
Many enterprise solutions
must address client access
to services and applications
based on connections to
selected TCP/IP addresses,
protocols, and port
numbers.
6 Module 8: Concepts of A Network Load Balancing Cluster
Network Load Balancing Features
Windows 2000 Network Load Balancing service provides the following
configuration, performance, and management features:
TCP/IP support. Services and applications can be delivered to the client by
using specified TCP/IP protocols and ports that can take advantage of
network load balancing.
Load balancing. Incoming client connections are load balanced among
cluster members based on a distributed algorithm that the Network Load
Balancing service executes and rules that you have configured for the
cluster.
High availability. Detects the failure of a host within the cluster, and within
seconds dynamically reconfigures and redistributes subsequent client
requests to hosts that are still viable members of the cluster.
Scalability. Removes or adds hosts without shutting down the cluster; the
maximum number of hosts that you can add within a cluster is 32 hosts.
Remote Manageability. Allows remote control of the cluster from any
Windows 2000 or Microsoft Windows NT
® system.
Network Load Balancing Driver
The Network Load Balancing service is a driver, Wlbs.sys, which you must
load on each member server, or host, in the cluster. Wlbs.sys includes a
statistical mapping algorithm that the cluster hosts collectively use to determine
which host handles each incoming request.
You install the driver on each of the cluster hosts, and you configure the cluster
to present a virtual IP address to client requests. The client requests go to all of
the hosts in the cluster, but only the mapped host accepts and handles the
request. All of the other hosts in the cluster drop the request.
Network Load Balancing Cluster Configuration
After you install the driver, you must configure it before the host can join a
cluster. You must configure three groups of information on each host: cluster
parameters, host parameters, and port rules, before it is possible to create or join
a cluster. Configuring the driver allows you to:
Select the cluster virtual IP address option.
Customize the cluster according to the various hosts’ capacities and sources
of client requests.
Specify that one host handles all of the client requests with the others
serving as failover alternatives.
Divide the load of incoming client requests among the hosts evenly or
according to a specified load partitioning weight.
Module 8: Concepts of A Network Load Balancing Cluster 7
Network Load Balancing Service Management
An administrator controls Network Load Balancing service by using the
command line utility, Wlbs.exe, which permits interactive and scripted
management of a cluster. You can use Wlbs.exe both locally and remotely to
control and administer a cluster and the member hosts. With Wlbs.exe you can:
Examine the status of a running network load balancing cluster.
Start and stop all or individual hosts in a network load balancing cluster.
Enable and disable rule processing for specified rules (port numbers).
8 Module 8: Concepts of A Network Load Balancing Cluster
Application and Service Environment
IIS Web site image
IIS Web site image
Virtual IP: 10.10.10.10
Virtual IP: 10.10.10.10
Web server TCP(80)
Web server TCP(80)
HTTPS
HTTPS
TCP(443)
TCP(443)
Port Rules define which
ports the cluster will
service
Affinity sets all client
connections to a single
host
IIS Web site image
IIS Web site image
Client TCP Session (Get)
Client TCP Session (Get)
Next client TCP Session (HTTPS)
Next client TCP Session (HTTPS)
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When a Web server application maintains state information about a client
session across multiple TCP connections, it is important that all TCP
connections for the client are directed to the same cluster host.
Network Load Balancing service can load balance any application or service
that uses TCP/IP as its network protocol and is associated with a specific TCP
or User Datagram Protocol (UDP) port. The distributed algorithm that is used to
determine which host responds to a TCP connection request or incoming UDP
packet can include the port number in the decision. Including the port number
in the decision means that for any client, different members of the Network
Load Balancing cluster may service connection requests or packets addressed to
different port numbers on the virtual IP address.
While configuring a network load balancing cluster, you need to consider
the type of application or service that the virtual server is providing, and select
the appropriate configuration for network load balancing hosts.
Port Rules
The Network Load Balancing driver uses port rules that describe which traffic
to load balance and which traffic to ignore. By default, the Network Load
Balancing driver configures all ports for load balancing. You can modify the
configuration of the Network Load Balancing driver that determines how
incoming network traffic is load balanced on a per-port basis by creating port
rules for each group of ports or individual ports as required. Each port rule
configures load balancing for client requests that use the port or ports covered
by the port range parameter. How you load-balance your applications is mostly
defined by how you add or modify port rules, which you create on each host for
any particular port range.
Topic Objective
To describe the application
and services configuration
for Network Load Balancing
hosts.
Lead-in
When a Web server
application maintains state
information about a client
session across multiple TCP
connections, it is important
that all TCP connections for
this client be directed to the
same cluster host.
Delivery Tips
Ensure that the students
understand how the
Network Load Balancing
driver can be configured to
manage application data
state and session state.
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