Network Availability (2.2 & 3.3) 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
Active-Active
▪ Multiple NICs are active at the same time
▪ NICs have their own MAC address
▪ Makes troubleshooting more complex
Active-Passive
▪ One NIC is active at a time
▪ Client appears to have a single MAC address
Network Interface Card Teaming
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
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
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
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
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
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
▪ 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
est 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