Card Set Information

2011-02-19 20:39:15

ont ch 4
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  1. Classification
    process of identifying and categorizing traffic into classes, typically based upon
  2. Classification uses a traffic what ?? to categorize a
    packet within a specific group
  3. Traffic descriptors include what
    Incoming interface

    IP precedence


    • Source or destination
    • address

  4. Without classification, all packets are treated the
  5. Classification should take place as close to the
    source " networks edge, within the ip phone or network endpoint"
  6. What is marking
    that “colors” a packet (frame) so it can be identified and distinguished from other packets (frames) in QoS treatment
  7. Local Link layer: Layer 2 frame What type of traffic
    CoS (ISL, 802.1p)

    MPLS EXP bits

    Frame Relay
  8. Network layer: packet header Layer 3 What type of traffic
    • DSCP
    • ip precedence
  9. Marking allows network devices to classify a packet or frame at the
    edge based on a specific traffic descriptor.
  10. Marking provides a way for QoS tools to change bits in the packet header to indicate
    the level of service this packet should receive from other QoS tools
  11. 802.1Q standard is an IEEE for what
    implementing VLANs in L2 switched networks
  12. what is 802.1p
    user priority field is also called CoS
  13. what is 802.1p
    supports up to 8 CoS
  14. The CoS marking uses the three 802.1p user priority
    bits and allows
    • Layer 2 Ethernet frame to be marked with eight
    • levels of priority (values 0–7).
  15. 802.1p focuses on what
    support for QoS over LANs and 802.1Q ports
  16. The three bits allow for what
    levels of classification
  17. What is a distavantage of CoS markings
    frames loose their CoS markings from an non 802.1q to a non 802.1p link.
  18. Trunking with 802.1Qmust be enabled befor what
    Cos field even exists
  19. 802.1p is preserved through what
    the LAN but not end to end.
  20. Canonical format indicator (CFI) (1 bit) is what
    • weather the bit order is canonical or noncanonical
    • used for capibility between eathernet and token ring networks
  21. VLAN identifier (VLAN ID) (12 bits):
    defines the VLAN used by 802.1Q, limits them to 4096
  22. Frame Relay provides a simple set of QoS mechanisms to ensure what
    CIR comitted information rate
  23. Frame Relay QoS
    • frames that exceed the committed rate can be marked as
    • discard eligible (DE) and droped in preference compared to ones not marked
  24. what does marking with MPLS
    • allows MPLS-enabled routers to perform QoS features indirectly based on the original IP Precedence
    • without spending resources
  25. The MPLS EXP field allows what
    the service provider to provide QoS without overwriting the value in the customer IP Precedence field
  26. MPLS frame
    • 32 bit label field
    • 8 CoSs
    • copies 3 most bits of DSCP to the EXP field
    • bits are presurved through MPLS network
  27. Describe the standard Per Hop Behavior (PHB)
    groups and their characteristics.
  28. DiffServ architecture is based on
    data packets that are placed into a limited number of traffic classes
  29. per-hop behaviors (PHBs)
    the packet forwarding properties associated with a class of traffic.
  30. what is behavior aggregate (BA)
    all the traffic flowing through a router that belongs to the same class
  31. The DSCP values mark packets to what
    select a PHB
  32. One of the primary principles of DiffServ is that you should
    mark packet as clost to the edge of the network as possible
  33. By marking the traffic at the network edge
    will quickly determin the proper CoS to a given traffic flow
  34. DuffServ is ease of what
  35. DiffServ is used for what
    mission critical application and end to end QoS
  36. Services are defined as what
    • QoS requirements and guarantees that are
    • provided to a collection of packets with the same DSCP value
  37. services are provided to what
  38. provisions are used to
    allocate resources to defined traffic classes
  39. DiffServ Model
    • Describes services associated with traffic
    • classes, rather than traffic flows.

    Complex traffic classification and conditioning is performed at the network edge.

    No per-flow state in the core.

    The goal of the DiffServ model is scalability.

    • Interoperability with non-DiffServ-compliant
    • nodes.

    Incremental deployment.
  40. IPv4:
    • three most significant bits of ToS byte
    • are called IP Precedence (IPP)—other bits unused
  41. three most significant bits of ToS byte
    IP Precedence(IPP)
  42. six most significant bits of ToS byte
    are called
    DiffServ Code Point (DSCP)
  43. DSCP is backward-compatible with
    IP precedence
  44. DiffServ maintains interoperability with
    non DiffServ compliant devices
  45. DiffServ can be deployed gradually in
    large networks
  46. The class selector PHB was defined to provide backward compatibility for
    DSCP with ToS based prcedence
  47. PHB is defined as
    • probaility of timely forwarding
    • basically Packets with higher IP
    • precedence should be (on average) forwarded in less time than packets with lower IP precedence.
  48. IP Precedence and DSCP Compatibility
    Compatibility with current IP precedence usage (RFC 1812)
  49. IP Precedence and DSCP Compatibility
    That is, if a packet has DSCP value of 011000, it has a greater probability of timely forwarding than a packet with DSCP value of 001000.
  50. Per-Hop Behaviors
    • is a description of the externally observable forwarding
    • behavior of a DiffServ node applied to a particular DiffServ behavior aggregate (BA).
  51. Useful behavioral distinctions are mainly observed when
    multiple BAs compete for buffer and bandwidth resources on a node.
  52. DSCP selects PHB throughout the network:
    Default PHB (FIFO, tail drop)

    Class-selector PHB (IP precedence)

    EF PHB

    AF PHB
  53. The DiffServ architecture defines the DiffServ (DS) field, which supersedes
    • the ToS field in IPv4 to make per-hop behavior (PHB)
    • decisions about packet classification and traffic conditioning functions, such as metering, marking, shaping, and policing.
  54. Metering is
    • the process of measuring the temporal properties (for
    • example, rate) of a traffic stream selected by a classifier.
  55. Marking is
    • the process of setting the DSCP in a packet based on
    • defined rules.
  56. Shaping is
    • the process of delaying packets within a traffic stream
    • to cause the traffic to conform to some defined traffic profile
  57. Policing is
    • the process of discarding packets within a traffic
    • stream in accordance with the state of a corresponding meter enforcing a traffic profile.
  58. Default PHB:
    • Used for best-effort service (bits 5 to 7 of DSCP equal
    • 000)
  59. Expedited Forwarding (EF) PHB:
    • Used for low-delay service (bits 5 to
    • 7 of DSCP equal 101)
  60. Assured Forwarding (AF) PHB:
    • Used for guaranteed bandwidth service
    • (bits 5 to 7 of DSCP equal 001, 010, 011, or 100)
  61. Class-selector PHB:
    Used for backward compatibility with non-DiffServ-compliant devices (RFC 1812-compliant devices; bits 2 to 4 of DSCP equal 000)
  62. Expedited Forwarding (EF) PHB
    EF PHB:
    Ensures a minimum departure rate

    Guarantees bandwidth—class guaranteed an amount of bandwidth with prioritized forwarding

    Polices bandwidth—class not allowed to exceed the guaranteed amount (excess traffic is dropped)
  63. Expedited Forwarding (EF) PHB
    DSCP value of 101110
    Looks like IP precedence 5 to non-DiffServ-compliant devices:

    Bits 5 to 7: 101 = 5 (same 3 bits are used for IP precedence)

    Bits 3 and 4: 11 = No drop probability

    Bit 2: Just 0
  64. Assured Forwarding (AF) PHB
    AF PHB:
    Guarantees bandwidth

    Allows access to extra bandwidth, if available

    • Four standard classes: AF1, AF2, AF3, and AF4
    • Each class should be treated independently and should have allocated bandwidth that is based on the QoS policy.
  65. Assured Forwarding (AF) PHB
    DSCP value range of aaadd0:
    • aaa is a binary value of the class
    • dd is drop probability
    • Packets requiring AF PHB should be marked with DSCP value aaadd0, where aaa is the number of the class and dd is the drop probability.
  66. AF PHB Values
    Each AF class uses three DSCP values.

    • Each AF class is independently forwarded with
    • its guaranteed bandwidth.

    Congestion avoidance is used within each class to prevent congestion within the class.
  67. Standard PHB Groups
    PHB group refers to the packet scheduling, queuing, policing, or shaping behavior of a node on any given packet belonging to a BA, as configured by a service level agreement (SLA) or a policy map.
  68. The default PHB specifies that a packet marked with a DSCP value of
    000000 (recommended) receives best-effort service from a DiffServ-compliant node.
  69. 4 AF classes
    • Each class is assigned a specific amount of buffer space and interface bandwidth. It is allowed to obtain bandwidth from other AF classes, if bandwidth is
    • available.
  70. The EF PHB defines one class, which assigns a fixed amount of
    bandwidth only for that class.
  71. how CoS is mapped to Layer 3 QoS.
    IP headers are preserved end to end when IP packets are transported across a network; data link layer headers are not preserved
  72. the most logical place to mark packets for end-to-end QoS
    ip layer
  73. To provide true end-to-end QoS, the ability to map QoS markings between the
    data link layer and the network layer is essential.
  74. remote LAN to provide end to end QoS requires
    CoS markings that are set at the LAN edge
  75. Campus and Wan routers map the QoS to new
    data link headers
  76. With mapping QoS can be what
    preserved and uniformly applied across the enterprise.
  77. DSCP bits can be mapped to
    CoSbits and vice versa
  78. DSCP bits can also be mapped to
    MPLS EXP bits and vice versa
  79. QoS classification mechanisms are used to
    separate traffic and identify packets as belonging to a specific service class.
  80. QoS mechanisms, such as policing, shaping, and
    queuing techniques, can be applied to each
    service class to meet the specifications of the administrative policy.
  81. A QoS service class can be:
    A single user (such as MAC address or IP address)

    A department, customer (such as subnet or interface)

    An application (such as port numbers or URL)

    A network destination (such as tunnel interface or VPN)
  82. A QoS service class
    is a logical grouping of packets that are to receive a similar level of applied quality
  83. three QoS service classes have been defined:
    Voice class
    Is to be treated with a strict high-priority service.
  84. three QoS service classes have been defined:
    Business applications class:
    Requires a guaranteed bandwidth of 20 percent and is to be given priority over web traffic.
  85. three QoS service classes have been defined:
    Web class:
    • Allowed to consume only up to 30 percent of any
    • WAN link.
  86. The remaining 15 percent is for
    management, signaling, and routing.
  87. Voice service class:
    Delivers low latency for voice services
  88. Mission-critical service class:
    • Guarantees latency and delivery for the transport
    • of mission-critical business applications, such as SAP
  89. Transactional service class:
    • Guarantees delivery and is used for more general
    • applications that are not that sensitive to delay compared to mission-critical applications
  90. Best-effort service class:
    • Used to support small business, e-mail, and other
    • best-effort applications
  91. QoS Service Class Guidelines
    • Profile applications to their basic network
    • requirements.

    • Do not over engineer provisioning; use no
    • more than four to five traffic classes for data traffic:

    Voice applications: VoIP

    Mission-critical applications: Oracle, SAP, SNA

    Interactive applications: Telnet, TN3270

    Bulk applications: FTP, TFTP

    Best-effort applications: E-mail, web

    Scavenger applications: Nonorganizational streaming and video applications (Kazaa, Yahoo)
  92. QoS Service Class Guidelines
    • Do not assign more than three applications to
    • mission-critical or transactional classes.

    • Use proactive policies before reactive
    • (policing) policies.

    • Seek executive endorsement of relative
    • ranking of application priority prior to rolling out QoS
    • policies for data.
  93. Marking 90 percent of network traffic as high priority
    will render most administrative QoS policies
  94. QoS must be implemented
    • consistently across the entire network. Whether the data
    • is crossing slow WAN links or Gigabit Ethernet,