Gartner Research

Availability and Resiliency

Published: 27 October 2008

ID: G00203575

Analyst(s): Jeff Young


Internet Protocol (IP) networking is a basic utility inside most enterprises and like another utility, the power grid, availability of IP networks drives the architecture of networks, the products that enterprises buy, and the services they use from different vendors. The task of the enterprise network architect is to deliver an always-on utility to different segments of the enterprise and to weigh the cost of providing resilient services versus the opportunity cost of a service outage. In a new look at availability and redundancy, Senior Analyst Jeff Young examines the tradeoffs for enterprise network architects.

Table Of Contents

Decision Point

Typical Requirements

  • Availability
  • Tradeoffs
    • Failure Modes
    • Resilience Through Redundancy


  • Network Hardware Resiliency
    • Load Balancing
    • “Hot” Redundant Hardware
  • Power Source Resiliency
  • Communication Path Resiliency
    • Dual Links
    • Dual-Homed Connections
    • Multiple Service Providers
    • Backup Networks
    • Network Recovery and Alternate Routing
  • Control Resource Resiliency
    • Default Gateway Redundancy
    • DNS Redundancy
    • Authentication and Policy Server Redundancy

Future Developments

  • Zero Downtime Software Reconfiguration
  • New Technology UPS Devices

Evaluation Criteria

Statement & Basis for Position

  • Network Hardware Resiliency Position
    • Devices that support LAN, MAN, and/or WAN backbone connectivity should contain redundancy features designed for expected uptime.
    • Spare equipment and redundant power supplies should be used to provide resiliency for devices that support mission-critical workgroups.
    • Resiliency for devices that support non-mission-critical workgroups is not necessary; however, should redundancy be desired, use spare equipment.
  • Power Source Resiliency Position
    • Major networking components serving data centers, mainframes, server farms, WAN gateways, and so forth will be configured and wired to ensure 100% electrical power availability.
    • Networking components in a campus backbone, or serving large or critical workgroups, will have redundant internal power supplies and an external UPS.
    • Power redundancy for small devices and those serving noncritical workgroups are treated as hardware redundancy at the box level with an external UPS.
  • Campus/Building Communications Path Resiliency Position
    • LAN Backbone Redundancy Position
    • Redundant Connectivity to the LAN Backbone Position
  • WAN Communications Path Resiliency Position
    • Sites that use IP, ATM, or MPLS and require WAN redundancy should implement diverse connections to the WAN. Also, if the WAN uses public ATM or IP services, then the diverse connections from a site should access different public carriers.
    • Sites that use WAN facilities and require backup WAN connectivity, but not 100% availability, should implement another form of resilient connectivity to provide an on-demand connection.
    • Sites that contain no mission-critical services or personnel should access the WAN through the least-expensive transport services and should not require redundant WAN connections.
  • Control Resource Resiliency Position
    • Devices that provide a control function or deliver a service required by users to establish or maintain network connections shall be fully redundant.
    • Servers and management stations not essential to communications on the network shall be supported by UPS power and spare hardware/software.

Relationship to Other Components


Revision History

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