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C480 Chapter 9

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verickle's version from 2016-10-26 19:24

High Availability

Question Answer
five nines of availabilityup 99.999 percent of the time, which translates to a maximum of 5 minutes of downtime per year
six nines of availability(it is up 99.9999 percent of the time), it is down less than 30 seconds per year
availabilityan available network is up and operational
reliabilityA reliable network, as an example, does not drop many packets.
MTTRmean time to repair
MTBFmean time between failures
Single points of failureIf the failure of a single network device or link (for example, a switch, router, or WAN connection) would result in an unavailable network
two modes of NIC redundancyActive-active, Active-standby
Active-activeBoth NICs are active at the same time, and each has its own MAC address. This makes troubleshooting more complex, while giving you slightly better performance than the Active-standby approach.
Active-standbyOnly one NIC is active at a time. This approach allows the client to appear to have a single MAC address and IP address, even in the event of a NIC failure.
Hot Standby Router Protocol (HSRP)A Cisco proprietary approach to first-hop redundancy.
Common Address Redundancy Protocol (CARP)an open-standard variant of HSRP. It allows multiple hosts on the same local area network to share a set of IP addresses.
Virtual Router Redundancy Protocol (VRRP)an IETF open standard that operates in a similar method to Cisco's proprietary HSRP. It provides for automatic assignment of available Internet Protocol (IP) routers to participating hosts.
Gateway Load Balancing Protocol (GLBP)another first-hop redundancy protocol that is proprietary to Cisco Systems. It attempts to overcome the limitations of existing redundant router protocols by adding basic load balancing functionality.
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QOS

Question Answer
Delaythe time required for a packet to travel from its source to its destination
Jitterthe uneven arrival of packets
Dropsoccur when a link is congested and a router's interface queue overflows
Classificationthe process of placing traffic into different categories. does not alter any bits in the frame or packet.
Markingalters bits within a frame, cell, or packet to indicate how the network should treat that traffic
Congestion ManagementWhen a device such as a switch or a router receives traffic faster than it can be transmitted, the device attempts to buffer (or store) the extra traffic until bandwidth becomes available.
Congestion AvoidanceIf an interface's output queue fills to capacity, newly arriving packets are discarded (or tail dropped).
Policingcan be used in either the inbound or the outbound direction, and it typically discards packets that exceed the configured rate limit, which you can think of as a speed limit for specific traffic types
traffic-shapingbuffers (and therefore delays) traffic exceeding a configured rate
committed information rate (CIR)the bandwidth for a virtual circuit guaranteed by an internet service provider to work under normal conditions
Link efficiencyA process of making the most of the limited bandwidth available on slower speed links by implementing compression or link fragmentation and interleaving (LFI)
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QoS Configuration Steps

Question Answer
1Determine network performance requirements for various traffic types
2Categorize traffic into specific categories
3Document your QoS policy and make it available to your users
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Three Categories of QoS Mechanisms

Question Answer Column 3
Best-effortuses a first–in, first–out (FIFO) queuing strategy, where packets are emptied from a queue in the same order that they entered the queueNot Strict
Integrated Services (IntServ)uses signaling among network devices to provide bandwidth reservations. must be configured on every router along a packet's pathLess Strict
Differentiated services (DiffServ)differentiates between multiple traffic flows. Specifically, packets are marked, and routers and switches can then make decisions (for example, dropping or forwarding decisions) based on those markings.Strict
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Glossary

Question Answer
AvailabilityThe measure of a network’s uptime.
ClassificationClassification is the process of placing traffic into different categories.
Committed information rate (CIR)The CIR of an interface is the average traffic rate over the period of a second.
Common Address Redundancy Protocol (CARP)An open standard variant of HSRP, which provides first-hop router redundancy.
Congestion avoidanceIf an interface’s output queue fills to capacity, newly arriving packets are discarded (or tail dropped). Congestion avoidance can prevent this behavior. RED is an example of a congestion-avoidance mechanism.
Congestion managementWhen a device, such as a switch or a router, receives traffic faster than it can be transmitted, the device attempts to buffer (or store) the extra traffic until bandwidth becomes available. This buffering process is called queuing or congestion management.
Differentiated services (DiffServ)As its name suggests, DiffServ differentiates between multiple traffic flows. Specifically, packets are marked, and routers and switches can then make decisions (for example, dropping or forwarding decisions) based on those markings.
Integrated services (IntServ)Often referred to as hard QoS because IntServ can make strict bandwidth reservations. IntServ uses signaling among network devices to provide bandwidth reservations. Resource Reservation Protocol (RSVP) is an example of an IntServ approach to QoS. Because IntServ must be configured on every router along a packet’s path, a primary drawback of IntServ is its lack of scalability.
JitterThe uneven arrival of packets.
LatencyThe measure of delay in a network.
Link efficiencyTo make the most of the limited bandwidth available on slower speed links, you might choose to implement compression or link fragmentation and interleaving (LFI). These QoS mechanisms are examples of link efficiency mechanisms.
MarkingAlters bits within a frame, cell, or packet to indicate how a network should treat that traffic. Marking alone does not change how a network treats a packet. Other tools (such as queuing tools) can, however, reference markings and make decisions (for example, forwarding decisions or dropping decisions) based on those markings.
PolicingInstead of making a minimum amount of bandwidth available for specific traffic types, you might want to limit available bandwidth. Both policing and traffic-shaping tools can accomplish this objective. Collectively, these tools are called traffic conditioners. Policing can drop exceeding traffic, as opposed to buffering it.
ReliabilityThe measure of how error-free a network transmits packets.
Traffic shapingInstead of making a minimum amount of bandwidth available for specific traffic types, you might want to limit available bandwidth. Both policing and shaping tools can accomplish this objective. Collectively, these tools are called traffic conditioners. Traffic shaping delays excess traffic by buffering it as opposed to dropping the excess traffic.
Uninterruptible power supply (UPS)An appliance that provides power to networking equipment in the event of a power outage.
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