Network Availability Flashcards
Network Availability
o Measure of how well a computer network can respond to connectivity and
performance demands that are placed upon it
High Availability
▪ Availability is measured by uptime
▪ Five nines of availability (99.999%)
▪ Maximum of 5 minutes of downtime per year
● Availability
o Concerned with being up and operational
● Reliability
o Concerned with not dropping packets
● Mean Time to Repair (MTTR)
o Measures the average time it takes to repair a network
device when it breaks
● Mean Time Between Failures (MTBF)
o Measures the average time between failures of a device
Redundant Network with Single Points of Failure
Link Redundancy (Multiple connections between devices)
● Internal Hardware Redundancy (Power supplies and NICs)
Redundant Network with No Single Points of Failure
Link Redundancy (Multiple connections between devices)
● Redundancy of Components (Switches and Routers)
Hardware Redundancy
▪ Takes many forms
▪ Devices with two network interface cards (NICs), hard drives, or internal
power supplies
Often found in strategic network devices
● Routers, Switches, Firewalls, and Servers
● Not often found in clients due to costs and administrative
overhead involved in management
o Active-Active
▪ Multiple NICs are active at the same time
▪ NICs have their own MAC address
▪ Makes troubleshooting more complex
o Active-Passive
▪ One NIC is active at a time
▪ Client appears to have a single MAC address
Network Interface Card Teaming
Using a group of network interface cards for load balancing and failover
on a server or other device
Layer 3 Redundancy
▪ Clients are configured with a default gateway (router)
● If the default gateway goes down, they cannot leave the subnet
● Layer 3 Redundancy occurs with virtual gateways
o Hot Standby Router Protocol (HSRP)
▪ Proprietary first-hop redundancy by Cisco
▪ Allows for active router and standby router
▪ Creates virtual router as the default gateway
o Virtual Router Redundancy Protocol (VRRP)
▪ IETP open-standard variant of HSRP
▪ Allows for active router and standby router
▪ Creates virtual router as the default gateway
o Gateway Load Balancing Protocol (GLBP)
▪ Proprietary first-hop redundancy by Cisco
▪ Focuses on load balancing over redundancy
▪ Allows for active router and standby router
▪ Creates virtual router as the default gateway
o Link Aggregation Control Protocol (LACP)
▪ Achieves redundancy by having multiple links
between devices
▪ Load balancing occurs over multiple links
▪ Multiple links appear as single logical link
Multipathing
Creates more than one physical path between the server and its storage
devices for better fault tolerance and performance
Design Considerations
Where will redundancy be used?
● Module (or Parts) Redundancy
● Chassis Redundancy
▪ What software redundancy features are appropriate?
▪ What protocol characteristics affect design requirements?
▪ What redundancy features should be used to provide power to an
infrastructure device?
▪ What redundancy features should be used to maintain environmental
conditions?
Best Practices
Examine the technical goals
▪ Identify the budget to fund high availability features
▪ Categorize business applications into profiles
● Each requires a certain level of availability
▪ Establish performance standards for high-availability solutions
● Performance standards will drive how success is measured
▪ Define how to manage and measure the high-availability solution
● Metrics help quantify success to decision makers
o Remember…
▪ Existing networks can be retrofitted, but it reduces the cost by integrating
high availability practices and technologies into your initial designs
Cold Sites
An available building that does not have any hardware or software in
place or configured
▪ While recovery is possible, it is going to be slow and time-consuming
o Warm Sites
An available building that already contains a lot of the equipment
▪ Restoral time is between 24 hours and seven days
Hot Sites
An available building that already has the equipment and data in place
and configured
▪ Minimal downtime and with nearly identical service levels maintained
Cloud Site
Allows for the creation of a recovery version of an organization’s
enterprise network in the cloud
● Recovery Time Objective (RTO)
o Time and service level within which a business process
must be restored after a disaster to avoid unacceptable
consequences
o How much time did it
take to recover after the notification of a business process
disruption?
o Use either a hot site or a cloud site for low RTO situations
● Recovery Point Objective (RPO)
o Interval of time during a disruption before data lost
exceeds the BCP’s maximum allowable threshold or
tolerance
Backup and Recovery
▪ Full
● Complete backup is the safest and most comprehensive; Time
consuming and costly
▪ Incremental
● Backup only data changed since last backup
▪ Differential
● Only backups data since the last full backup
▪ Snapshots
● Read-only copy of data frozen in time (VMs)
