Designing the WAN Environment
This section addresses how the technical data from Section 7,
Conceptual Overview can be used to evaluate different WAN interconnect technologies to achieve the business and technical objectives of Rainpole.com’s specific use case.
Figure 3. Determining WAN Infrastructure Factors
To determine the most appropriate cross-data center WAN interconnect that meets the business requirements, the features of different WAN technology systems must be evaluated. The design decision must be centered on the technology and the business requirements that have been established. In the sample use case, the key factors in determining the most appropriate solution are the bandwidth and latency requirements for the application mobility use case, although other factors such as data replication and management access can provide additional design considerations. In this case, application mobility refers to online migration over distance with vSphere vMotion. Because each vSphere vMotion operation across the WAN link requires 250 MB of available bandwidth, there is clear potential for a significant amount of traffic flooding the link if it is not appropriately architected, and if operational procedures, such as managed change, are not in place for the live cross-site migration of workloads.
Design considerations for the type of WAN employed in the design include the following.
Table 1. WAN Design Considerations
Design Consideration | Description |
Distance | WAN solutions are typically implemented at the physical layer and often include a distance limitation. While distances for DWDM are significant, this is probably not suitable for a cross-country solution. SONET, MPLS, and IP have essentially unlimited distances because they span across multiple providers’ infrastructure. |
Speed (bandwidth and latency) | Because you are the owner, private WAN solutions offer guaranteed bandwidth and latency, and can control the usage of the infrastructure and establish appropriate QoS policies. However, these leased solutions can often be more complex than alternatives. Dedicated physical solutions, such as dark fibre, CWDN, and DWDM provide a guaranteed amount of bandwidth and a known level of latency due to the way the solution is provisioned. SONET is similar because it generally uses underlying infrastructure that is provisioned physically. MPLS and IP use shared environments and are therefore subject to spikes in data transmission. These types of solutions can lease a specific amount of bandwidth from a provider, but there might be periods of time when full bandwidth is unavailable because it is typically over-provisioned by the provider. |
Cost | Deploying a privately owned solution requires the purchase of the necessary equipment and the media itself. Some equipment, such as DWDM optics and multiplexers can come at a very high cost. Leased line solutions might include some or all of the required equipment in the cost. However, it is typical that the service consumer must still purchase equipment to integrate into the VMware Cloud Provider’s solution. |
Redundancy | With dark fibre, CWDM, and DWDM solutions, it can prove difficult to obtain connectivity across two physically separate and diverse paths. Having multiple fibers in the same bundle for redundancy might increase exposure to the risk of a complete communications failure due to a break in the media. One approach to protect against this type of communication failure is to use a different solution, such as MPLS or IP, as a backup. Additionally, leased line solutions using multiple providers might also provide additional redundancy in the event of a provider-wide outage. |
WAN links can broadly be defined as one of the following three options:
• Private WAN: Owned and managed by the user’s business. They are expensive and potentially very labor intensive to implement and maintain. They can also be difficult to reconfigure for dynamically changing business requirements. The primary advantages of using private WAN links include higher levels of security and transmission quality.
• Leased WAN: Maintained by a service provider, although the user’s business might be required to purchase additional hardware to provide connectivity. The consumer typically pays for the allocated bandwidth regardless of its utilization.
• Shared WAN: A shared environment where the service provider is responsible for all operational maintenance, although the user’s business might be required to purchase additional hardware to provide connectivity. While a shared WAN link is typically the least expensive option to deploy and maintain, they also bare the highest security risks and the potential for resource conflicts, depending on configuration.
