Network Availability Flashcards
Availability
Concerned with being up & operational
Reliability
Concerned with not dropping packets
MTTR
Mean Time to Repair
Measures the average time it takes to repair a network device when it breaks
MTBF
Mean Time Between Failures
Measures the average time between failures of a device
Redundant Networks w/Single Point of Failure
Link Redundancy:
Internal Hardware Redundancy
(PSUs & NICs)
Redundant Networks w/No Single Points of Failure
Link Redundancy:
Redundancy of Components
(Switches & Routers)
Hardware Redundancy
(Takes many forms)
Devices with two NICs, HDDs/SSDs, or internal PSUs
Often found in strategic network devices
(Routers/Switches/Firewalls/Servers)
Usually not found in clients due to cost
Hardware Redundancy: Active-Active
Multiple NICs are active at the same time
NICs have their own MAC addresses
Makes troubleshooting more complex
Hardware Redundancy: Active-Standby
One NIC is active at a time
Client appears to have a single MAC address
Layer 3 Redundancy
Clients are configured with a default gateway (router)
If default gateway goes down, they cannot leave subnet
Layer 3 redundancy creates virtual gateways to avoid this issue
HSRP
Hot Standby Router Protocol:
Proprietary first-hop redundancy by Cisco
Allows for active router and standby router
Creates virtual router as the default gateway
CARP
Common Address Redundancy Protocol:
Open-standard variant of HSRP
Allows for active & standby router
Creates virtual router as default gateway
VRRP
Virtual Router Redundancy Protocol:
IETP open-standard variant of HSRP
Allows for active & standby router
Creates virtual router as default gateway
GLBP
Gateway Load Balancing Protocol:
Proprietary first-hop redundancy by Cisco
Focuses on load balancing over redundancy
Allows for active & standby router
Creates virtual router as default gateway
LACP
Ling Aggregation Control Protocol:
Achieves redundancy by having multiple links between devices
Load balancing occurs over multiple links
Multiple links appear as a single logical link
Availability Best Practices
Examine technical goals
Identify budget to fund high avail features
Categorize business apps into profiles
(Each requires certain level of availability)
Establish performance standards
Define how to manage & measure the solution
(Need metrics to quantify success)
Recovery Sites: Cold Sites
Building is available, but no hardware/software configured
Need to buy resources (or ship them in) and the configure network
Slow & time consuming recovery
Recovery Sites: Warm Sites
Building & equipment available
Software may not be installed & latest data unavailable
Recovery is fairly quick, but not everything from original site is available to employees
Recovery Sites: Hot Sites
Building, equipment, & data available
Software & hardware configured
Ready as soon as people walk in
Downtime is very minimal
Backup Types
Full: Complete backup (time consuming & costly)
Incremental: Backup only data changed since last backup
Differential: Backup only data since last full backup
Snapshots: Read-only copy of data frozen in time (VMs)
QoS
Quality of Service:
Enables strategic optimization of network performance for different types of traffic
Identifies types of traffic needing priority
Determines how much bandwidth required
Efficiently uses WAN link’s bandwidth
Identifies types of traffic to drop during network congestion
QoS Categories
Delay:
Time a packet travels from source to destination
Measured in ms
Jitter:
Uneven arrival of packets (harmful in VoIP/streaming)
Drops:
Occurs during link congestion
Router’s interface queue overflows & causes packet loss
QoS Traffic Categorization
Determine network performance requirements for various traffic types (voice, video, data, etc)
Low delay: Voice, video streaming
Low priority: Web browsing, non-mission critical data
QoS Traffic Categorization: Best Effort
Does not truly provide QoS to that traffic
No reordering of packets
Uses FIFO (first in, first out) queuing
QoS Traffic Categorization: IntServ
Integrated Services (IntServ/Hard QoS): Makes strict bandwidth reservations
Reserves bandwidth by signaling devices
QoS Traffic Categorization: DiffServ
Differentiated Services (DiffServ/Soft QoS):
Differentiates between multiple traffic flows
Packets are “marked”
Routers/switches make decisions based on markings
QoS Traffic Categorization Methods
Classification Marking Congestion management Congestion avoidance Policing & shaping Link efficiency
Marking of Traffic
Altered bits within a frame/cell/packet indicates handling of traffic
Network tools make decisions based on markings
Congestion Management
Queuing: When a device receives traffic faster than it can be transmitted, it buffers the extra traffic until bandwidth is available
Queuing algorithm empties the packets in specified sequence & amount
Queuing Algorithm types:
Weighted fair queuing
Low-latency queuing
Weighted round-robin
Congestion Avoidance
Newly arriving packets would be discarded if the device’s output queue fills to capacity
If TCP: Will be retransmitted
If UDP: Will be dropped
Congestion Avoidance: RED
Random Early Detection:
As the queue fills, the possibility of a discard increases until it reaches 100%
At 100%, all of that traffic type is dropped
RED instead drops packets from selected queues based on defined limits
Policing
Typically discards packets that exceed a configured rate limit (speed limit)
Recommended for higher-speed interfaces
Shaping
Buffers (delays) traffic exceeding configured rate
Recommended for slower-speed interfaces
Link Efficiency: Compression
Packet payload is compressed to conserve bandwidth
VoIP payload can be reduced by 50%
(40 bytes to 20 bytes)
VoIP header can be reduced by 90-95%
Uses RTP header compression (cRTP)
(40 bytes to 2-4 bytes)
Utilized on slower-speed links to make most of limited bandwidth
Link Efficiency: LFI
Link Fragmentation & Interleaving:
Fragments large data packets & interleaves smaller data packets between the fragments
Utilized on slower-speed links to make the most of limited bandwidth
Multipathing
Creates more than one physical path between the server & its storage devices for better fault tolerance & performance
Designing Redundant Networks
Examine technical/operational goals
Identify the budget to fund high-availability features
Categorize business apps into profiles
Establish performance standards for high-availability solutions
Define how to manage & measure the high-availability solutions
(Time vs Cost vs Quality)
Recovery Sites: Cloud Site
Allows for the creation of a recovery version of an organization’s enterprise network in the cloud
Recovery Sites: Cloud Site - RTO
Recovery Time Objective:
Time & service level within which a business process must be restored after a disaster to avoid unacceptable consequences
How much time did it take to recovery after the notification of a business process disruption?
For low RTO situations: Use a hot or cold site
Recovery Sites: Cloud Site - RPO
Recovery Point Objective:
Interval of time during a disruption before data lost exceeds the BCP’s (business continuity plan) maximum allowable threshold or tolerance
Facilities Support: UPS
Uninterruptible Power Supply:
Provides emergency power to a load when the input power source or main power fails
Great for short duration power outages (less than 15 minutes)
Facilities Support: PDU
Power Distribution Unit:
Distributes electric power, especially to racks of computers & networking equipment located within a data center
PDUs combined with a UPS or generator can provide power during a blackout
Facilities Support: Generator
Provides long-term power during a power outage in a region
Takes a while to start up
Hot & cold aisle concept
Facilities Support: Wet Pipe System
Using a sprinkler system & pipes that always contain water
Facilities Support: Pre-Action System
A detector actuation like a smoke detector & a sprinkler must be tripped prior to water being released
