Section 17: Network Availability
Which of the following type of sites would contain little to no hardware and could take days or weeks to become ready for use during a disaster? - Quiz 16: Network Availability
A cold site is a backup facility with little or no hardware equipment installed. A cold site is essentially an office space with basic utilities such as power, cooling system, air conditioning, and communication equipment, etc.
Cloud Sites : (Recovery) - Network Availability
Allows for the creation of a recovery version of an organization's enterprise network in the cloud
Marking of Traffic : (QoS Mechanisms) - Network Availability
Altered bits within a frame, cell, or packet indicates handling of traffic ▪ Network tools make decisions based on markings
Which of the following would be the BEST addition to a business continuity plan to protect the business from a catastrophic disaster such as a fire, tornado, or earthquake? - Quiz 16: Network Availability
Although all answers are adequate suggestions to aid in business continuity, the addition of a hot or cold site is the BEST option. A hot or cold site is a commercial service that provides all equipment and facilities to allow a computer or networking company to continue operations in the event of a catastrophic event. In the case that the building has been destroyed, the hot/cold site is the only option that will allow the business to continue their operations effectively.
Warm Sites : (Recovery) - Network Availability
An available building that already contains a lot of the equipment ▪ Restoral time is between 24 hours and seven days
Hot Sites : (Recovery) - Network Availability
An available building that already has the equipment and data in place and configured ▪ Minimal downtime and with nearly identical service levels maintained
Cold Sites : (Recovery) - Network Availability
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
You have been dispatched to investigate some sporadic network outages. After looking at the event logs for the network equipment, you found that the network equipment has been restarting at the same time every day. What should you implement to correct this issue? - Quiz 16: Network Availability
An uninterruptible power supply (UPS) is a battery system that can supply short-term power to electrical units. Since all the devices are restarting simultaneously, it is likely due to a power outage. In this case, a UPS would continue to supply power to the network equipment during outages or blackouts.
Incremental : (Backup and Recovery) - Network Availability
Backup only data changed since last backup
Layer 3 Redundancy - Network Availability
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
Full : (Backup and Recovery) - Network Availability
Complete backup is the safest and most comprehensive; Time consuming and costly
Availability : (Components of High Availability Networks) - Network Availability
Concerned with being up and operational
Reliability : (Components of High Availability Networks) - Network Availability
Concerned with not dropping packets
Multipathing - Network Availability
Creates more than one physical path between the server and its storage devices for better fault tolerance and performance
Categorization of Traffic : (Types of Quality of Service (QoS) Catgeorizations) - Network Availability
Determine network performance requirements for various traffic types (Voice, Video, Data) ▪ Categorize traffic into specific categories: ● Low delay - Voice - Streaming Video ● Low priority - Web browsing - Non-mission critical data ▪ Document your QoS policy and make it available to your users
Quality of Service (QoS) : (Quality of Service (QoS) ) - Network Availability
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 ▪ For example: - Voice (VoIP) and Video should have higher priority levels (less latency)
Remember : (Components of Designing Redundant Networks) - Network Availability
Existing networks can be retrofitted, but it reduces the cost by integrating high availability practices and technologies into your initial designs
Which of the following is designed to keep the system's uptime running in the event of a disaster? - Quiz 16: Network Availability
High availability (HA) is a component of a technology system that eliminates single points of failure to ensure continuous operations or uptime for an extended period. If a network switch or router stops operating correctly (meaning that a network fault occurs), communication through the network could be disrupted, resulting in a network becoming unavailable to its users. Therefore, network availability, called uptime, is a major design consideration for high availability networks.
Recovery Point Objective (RPO) : (Cloud Sites / Recovery) - Network Availability
Interval of time during a disruption before data lost exceeds the BCP's maximum allowable threshold or tolerance
Link Efficiency: LFI : (QoS Mechanisms) - Network Availability
Link Fragmentation & Interleaving (LFI) ▪ Fragments large data packets and interleaves smaller data packets between the fragments ▪ Utilized on slower-speed links to make the most of limited bandwidth
Redundant Network with Single Points of Failure : (High Availability Networks) - Network Availability
Link Redundancy (Multiple connections between devices) ● Internal Hardware Redundancy (Power supplies and NICs)
Redundant Network with No Single Points of Failure : (High Availability Networks) - Network Availability
Link Redundancy (Multiple connections between devices) ● Redundancy of Components (Switches and Routers)
Integrated Services (IntServ or Hard QoS) : (Ways of Categorizing Traffic / Types of Quality of Service (QoS) Catgeorizations) - Network Availability
Makes strict bandwidth reservations ● Reserves bandwidth by signaling devices
Network Availability
Measure of how well a computer network can respond to connectivity and performance demands that are placed upon it
Mean Time Between Failures (MTBF) : (Components of High Availability Networks) - Network Availability
Measures the average time between failures of a device
Mean Time to Repair (MTTR) : (Components of High Availability Networks) - Network Availability
Measures the average time it takes to repair a network device when it breaks
Congestion Avoidance : (QoS Mechanisms) - Network Availability
Newly arriving packets would be discarded if the device's output queue fills to capacity Random Early Detection (RED) is used to prevent this from occurring ● As the queue fills, the possibility of a discard increases until it reaches 100% ● If at 100%, all traffic of that type is dropped ● RED instead drops packets from selected queues based on defined limits If TCP traffic, it will be retransmitted If UDP, it will simply be dropped
Drops : (Categories of QoS / Quality of Service (QoS) ) - Network Availability
Occurs during link congestion ● Router's interface queue overflows and causes packet loss
Differential : (Backup and Recovery) - Network Availability
Only backups data since the last full backup
Link Efficiency: Compression : (QoS Mechanisms) - Network Availability
Packet payload is compressed to conserve bandwidth ▪ VoIP payload can be reduced by 50% - Payload size from 40 bytes to 20 bytes VoIP header can be reduced by 90-95% ● Uses RTP header compression (cRTP) ● Header size goes from 40 bytes to 2 to 4 bytes ▪ Utilized on slower-speed links to make most of limited bandwidth
Policing and Shaping : (QoS Mechanisms) - Network Availability
Policing ● Typically discards packets that exceed a configured rate limit (speed limit) ● Dropped packets result in retransmissions ● Recommended for higher-speed interfaces Shaping ● Buffers (delays) traffic exceeding configured rate ● Recommended for slower-speed interfaces
At which of the following OSI layer does QoS operate? - Quiz 16: Network Availability
Quality of Service (QoS) occurs at both Layer 2 and Layer 3 of the OSI Model. Layer 2 Quality of Service (QoS) allows for traffic prioritization and bandwidth management to minimize network delay using Cost of Service (CoS) classification, and DSCP marking under the 802.1p standard. Layer 3 Quality of Service (QoS) allows for managing the quality of network connections through its packet routing decisions.
Snapshots : (Backup and Recovery) - Network Availability
Read-only copy of data frozen in time (VMs)
Delay : (Categories of QoS / Quality of Service (QoS) ) - Network Availability
Time a packet travels from source to destination ● Measured in milliseconds (ms)
Purpose of QoS : (Types of Quality of Service (QoS) Catgeorizations) - Network Availability
To categorize traffic, apply a policy to those traffic categories, and prioritize them in accordance with a QoS policy
Classification of Traffic : (QoS Mechanisms) - Network Availability
Traffic is placed into different categories ▪ For example, the E-mail class might contain various types of traffic ● POP3 ● IMAP ● SMTP ● Exchange Classification does not alter any bits in the frame or packet
Jitter : (Categories of QoS / Quality of Service (QoS) ) - Network Availability
Uneven arrival of packets ● Especially harmful in VoIP
Network Interface Card Teaming - Network Availability
Using a group of network interface cards for load balancing and failover on a server or other device
Congestion Management : (QoS Mechanisms) - Network Availability
When a device receives traffic faster than it can be transmitted, it buffers the extra traffic until bandwidth becomes available - Called queuing ▪ Queuing algorithm empties the packets in specified sequence and amount ▪ Queuing algorithms types - Weighted fair queuing - Low-latency queuing - Weighted round-robin
Design Considerations : (Components of Designing Redundant Networks) - Network Availability
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?
Recovery Time Objective (RTO) : (Cloud Sites / Recovery) - Network Availability
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
Link Aggregation Control Protocol (LACP) : (Layer 3 Redundancy) - Network Availability
▪ Achieves redundancy by having multiple links between devices ▪ Load balancing occurs over multiple links ▪ Multiple links appear as single logical link
High Availability : (High Availability Networks) - Network Availability
▪ Availability is measured by uptime ▪ Five nines of availability (99.999%) ▪ Maximum of 5 minutes of downtime per year
Methods of Categorizing Traffic : (Ways of Categorizing Traffic / Types of Quality of Service (QoS) Catgeorizations) - Network Availability
▪ Classification ▪ Marking ▪ Congestion management ▪ Congestion avoidance ▪ Policing and shaping ▪ Link efficiency
Ways of Categorizing Traffic : (QoS Mechanisms) - Network Availability
▪ Classification ▪ Marking ▪ Congestion management ▪ Congestion avoidance ▪ Policing and shaping ▪ Link efficiency
Best Practices : (Components of Designing Redundant Networks) - Network Availability
▪ 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
Virtual Router Redundancy Protocol (VRRP) : (Layer 3 Redundancy) - Network Availability
▪ IETP open-standard variant of HSRP ▪ Allows for active router and standby router ▪ Creates virtual router as the default gateway
Active-Active : (Types of Hardware Redundancy / High Availability Networks) - Network Availability
▪ Multiple NICs are active at the same time ▪ NICs have their own MAC address ▪ Makes troubleshooting more complex
Need for Quality of Service (QoS) : (Quality of Service (QoS) ) - Network Availability
▪ Networks carry data, voice, and video content ▪ Convergence of media on the network requires high availability to ensure proper delivery ▪ Optimizing the network to efficiently utilize the bandwidth to deliver useful solutions to network users is crucial to success and cost savings
Active-Passive : (Types of Hardware Redundancy / High Availability Networks) - Network Availability
▪ One NIC is active at a time ▪ Client appears to have a single MAC address
Hot Standby Router Protocol (HSRP) : (Layer 3 Redundancy) - Network Availability
▪ Proprietary first-hop redundancy by Cisco ▪ Allows for active router and standby router ▪ Creates virtual router as the default gateway
Gateway Load Balancing Protocol (GLBP) : (Layer 3 Redundancy) - Network Availability
▪ 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
Hardware Redundancy : (High Availability Networks) - Network Availability
▪ 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
Differentiated Services (DiffServ or Soft QoS) : (Ways of Categorizing Traffic / Types of Quality of Service (QoS) Catgeorizations) - Network Availability
● Differentiates between multiple traffic flows ● Packets are "marked" ● Routers and switches make decisions based on those markings
Best Effort : (Ways of Categorizing Traffic / Types of Quality of Service (QoS) Catgeorizations) - Network Availability
● Does not truly provide QoS to that traffic ● No reordering of packets ● Uses FIFO (first in, first out) queuing
