Example: Ensuring Availability in NLB Solutions

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Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

An organization provides VPN remote access to the organization’s users through the Internet. The organization’s design includes Network Load Balancing to eliminate any application outages and improve performance. The VPN remote access servers, running Routing and Remote Access and Windows Server 2003, reside in the organization’s perimeter network, which is located between the Internet and the organization’s private network.

The design includes ISA Server, which protects the VPN remote access servers in the perimeter network. The ISA Server servers are in a cluster (ISANLB-01) that provides load balancing and fault tolerance.

During the pilot testing of the Web content caching solution, with ISA Server, the deployment team experiences a number of outages that affect the entire solution. Figure 8.18 illustrates the Web content caching design, incorporating ISA Server, that is tested.

Figure 8.18   VPN Remote Access Test Environment

VPN Remote Access Test Environment

Table 8.25 lists the results of the pilot test for each portion of the design that is illustrated in Figure 8.18.

Table 8.25   Results of VPN Pilot Test

Design Portion Tested Results

Network infrastructure
  • A failure of Router-01 resulted in total outage of VPN services.

  • A failure of Switch-01 resulted in total outage of VPN services.

  • A total outage of VPN services occurred for failure of the network segment between Router-01 and the Internet, or between Switch-01 and Router-01.

Cluster host hardware
  • A failure of a disk drive in a cluster host resulted in a total cluster host failure.

  • Network adapters in the cluster hosts have unsigned device drivers.

After the pilot test, the VPN remote access design is modified. Figure 8.19 illustrates the modified version of the VPN design.

Figure 8.19   Revised VPN Remote Access Design

Revised VPN Remote Access Design

Table 8.26 lists the design decisions that the organization makes to improve the uptime for the VPN remote access solution and the reasons for making those decisions.

Table 8.26   Improving VPN Solution Uptime Design Decisions and Their Justification

Decision Reason for the Decision

Added Router-02 and additional Internet connection.

Provides a redundant route path to the Internet in the event that Router-01 or the corresponding Internet connection fails.

Added Switch-02.

Provides redundant paths in the event that Switch-01 fails.

RAID disk controllers were used in each cluster host.

Provide disk fault tolerance to help prevent disk failures and cluster host failures.

Group Policy was established to allow cluster hosts to load signed device drivers.

Provides trusted software to help ensure a stable environment, and prevents cluster host failure.