W4 ch2
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Questions and Answers

What is the main function of the control plane in MPLS?

  • Routing IP packets based on destination prefixes
  • Forwarding data packets
  • Assigning labels to IP packets
  • Identifying reachability to destination prefixes (correct)

    • What type of information is exchanged between neighboring routers in the control plane?

  • Label values
  • QoS policies
  • IP routing information (correct)
  • Layer 2 MAC addresses

    • What is the source of the information in the data plane?

  • Control plane (correct)
  • Static configuration
  • Label distribution protocols
  • IP routing tables

    • What is the function of label distribution protocols?

    <p>Exchanging labels between neighboring routers</p> Signup and view all the answers

    What type of packets are forwarded in the data plane?

    <p>Either Layer 3 IP packets or labeled IP packets</p> Signup and view all the answers

    What is the result of information exchange between neighboring routers in the control plane?

    <p>Mappings of IP destination prefixes to labels are created</p> Signup and view all the answers

    What is the relationship between the control plane and data plane?

    <p>The control plane derives information for the data plane</p> Signup and view all the answers

    What is the function of the TTL field in MPLS?

    <p>To prevent looping of unwanted packets in the network</p> Signup and view all the answers

    What happens when the label TTL value is 0?

    <p>The packet is discarded</p> Signup and view all the answers

    Where is the label inserted in an IP packet?

    <p>Between the Frame Header and the Layer 3 Header</p> Signup and view all the answers

    What does the S bit in the label indicate?

    <p>The bottom of the label stack</p> Signup and view all the answers

    What is the most significant parameter that affects QoS?

    <p>Network Availability</p> Signup and view all the answers

    What does an egress Edge LSR do when it encounters the bottom of the label stack?

    <p>It performs a route lookup in the IP Layer 3 Header</p> Signup and view all the answers

    What is guaranteed bandwidth?

    <p>The minimum bandwidth allocated to a user</p> Signup and view all the answers

    What is the purpose of label stacks in MPLS?

    <p>To implement MPLS-based services such as MPLS VPN and MPLS traffic engineering</p> Signup and view all the answers

    What is the primary reason for oversubscribing bandwidth?

    <p>To maximize return on investment of network infrastructure</p> Signup and view all the answers

    What does the second label in the label stack identify in MPLS VPN?

    <p>The VPN</p> Signup and view all the answers

    What is the purpose of emission priority in QoS?

    <p>To provide traffic management mechanisms</p> Signup and view all the answers

    How can network operators increase network availability?

    <p>By implementing varying degrees of redundancy and resilient networking protocols</p> Signup and view all the answers

    What does the top label in the label stack identify in Layer 2 VPN implementations?

    <p>The Tunnel Header or endpoint</p> Signup and view all the answers

    What is the relationship between available bandwidth and subscribed bandwidth?

    <p>Available bandwidth is often less than subscribed bandwidth due to oversubscription</p> Signup and view all the answers

    What is jitter in the context of QoS?

    <p>Variation in packet delay</p> Signup and view all the answers

    Which of the following is NOT a QoS performance dimension?

    <p>Security</p> Signup and view all the answers

    What is the primary function of TCP in a network?

    <p>To provide packet loss protection</p> Signup and view all the answers

    What happens to network performance when congestion persists?

    <p>It significantly decreases</p> Signup and view all the answers

    What is the purpose of Random Early Discard (RED) algorithms?

    <p>To provide efficient congestion management</p> Signup and view all the answers

    What type of applications does RED provide effective congestion control for?

    <p>Applications with TCP-like throttling mechanisms</p> Signup and view all the answers

    What happens to TCP's transmission window size when congestion persists?

    <p>It decreases in size</p> Signup and view all the answers

    Why do applications have different QoS requirements?

    <p>Because they have different performance dimensions</p> Signup and view all the answers

    What is the result of mixing applications with different QoS requirements over a common IP transport network without QoS technologies?

    <p>Unpredictable traffic behavior</p> Signup and view all the answers

    What is the primary goal of congestion avoidance mechanisms?

    <p>To prevent network congestion</p> Signup and view all the answers

    What was the traditional approach to networking for different applications?

    <p>Separate, dedicated networks for each type of application</p> Signup and view all the answers

    What is the primary motivation for consolidating separate networks into one?

    <p>To reduce operational costs and improve profit margins</p> Signup and view all the answers

    What type of network has voice applications traditionally operated on?

    <p>A TDM-based voice network</p> Signup and view all the answers

    What is the primary characteristic of voice traffic in a steady-state fashion?

    <p>No packet loss and a minimal but fixed amount of packet delay</p> Signup and view all the answers

    What is the resulting issue when running voice applications over a best-effort IP network?

    <p>The voice application reacts unfavorably with other traffic types</p> Signup and view all the answers

    What is the trend for data networks in terms of transport technology?

    <p>Converging on IP transport</p> Signup and view all the answers

    Why did QoS technologies play a smaller role in traditional networks?

    <p>Because the traffic was similar in behavior and the dedicated networks were fine-tuned to meet the required behavior</p> Signup and view all the answers

    What is the impact of converging different types of traffic on a single network?

    <p>The traffic types react unfavorably with each other</p> Signup and view all the answers

    What is the foundation on which MPLS and its services operate on a Cisco router?

    <p>Cisco Express Forwarding (CEF)</p> Signup and view all the answers

    What is the purpose of the Forwarding Information Base (FIB) in a Cisco router?

    <p>To mirror the entire contents of the IP routing table</p> Signup and view all the answers

    What is an adjacency in the context of a Cisco router?

    <p>A network node that can reach one another with a single hop across the link layer</p> Signup and view all the answers

    What are the two other structures maintained in a Cisco router in addition to the FIB?

    <p>LIB and LFIB</p> Signup and view all the answers

    What is responsible for creating entries in the LIB and LFIB?

    <p>The distribution protocol in use between adjacent MPLS neighbors</p> Signup and view all the answers

    What is stored in the FIB table?

    <p>Destination networks in the routing table to appropriate next-hop adjacencies</p> Signup and view all the answers

    What is the relationship between FIB table and routing table entries?

    <p>One-to-one mapping</p> Signup and view all the answers

    Where does the FIB reside in a Cisco router?

    <p>Data plane</p> Signup and view all the answers

    What is the difference between liberal and conservative label retention modes?

    <p>One discards labels from non-next-hop routers, the other maintains all labels</p> Signup and view all the answers

    What happens to the incoming MPLS packet when it is associated with an untagged outgoing label?

    <p>It is converted to an IP packet and forwarded to the destination</p> Signup and view all the answers

    What is the purpose of special outgoing labels?

    <p>To define the operation to be performed at the upstream LSR or router</p> Signup and view all the answers

    What is the benefit of conservative label retention mode?

    <p>It consumes minimal memory</p> Signup and view all the answers

    What is the difference between downstream on demand and unsolicited downstream distribution?

    <p>One waits for a request, the other sends label mapping information without a request</p> Signup and view all the answers

    What happens when an LSR supports liberal label retention mode?

    <p>It maintains bindings between labels and destination prefixes, even from non-next-hop routers</p> Signup and view all the answers

    What is the result of using liberal label retention mode?

    <p>Larger number of labels maintained for a particular destination, consuming memory</p> Signup and view all the answers

    What happens when the TTL value of a packet reaches 0?

    <p>The packet is discarded to prevent looping</p> Signup and view all the answers

    Where is the label inserted in an IP packet?

    <p>Between the Layer 2 and Layer 3 headers</p> Signup and view all the answers

    What does the S bit in the label indicate?

    <p>The bottom of the label stack</p> Signup and view all the answers

    What is the purpose of label stacks in MPLS?

    <p>To implement MPLS-based services</p> Signup and view all the answers

    What does an egress Edge LSR do when it encounters the bottom of the label stack?

    <p>It performs a route lookup and forwards the packet</p> Signup and view all the answers

    What does the second label in the label stack identify in MPLS VPN?

    <p>The VPN</p> Signup and view all the answers

    What does the top label in the label stack identify in Layer 2 VPN implementations?

    <p>The Tunnel Header or endpoint</p> Signup and view all the answers

    What is the purpose of label stacks in MPLS traffic engineering?

    <p>To identify the endpoint of the TE tunnel</p> Signup and view all the answers

    What is the primary goal of congestion avoidance mechanisms?

    <p>To avoid network congestion</p> Signup and view all the answers

    What happens to TCP's transmission window size when congestion persists?

    <p>It decreases to reduce packet transmission</p> Signup and view all the answers

    What type of applications does Random Early Discard (RED) provide effective congestion control for?

    <p>Applications with TCP-like throttling mechanisms</p> Signup and view all the answers

    What happens when a network becomes increasingly congested?

    <p>More packets are dropped, leading to retransmission</p> Signup and view all the answers

    What is the result of mixing applications with different QoS requirements over a common IP transport network without QoS technologies?

    <p>Unpredictable network behavior</p> Signup and view all the answers

    Why do applications have different QoS requirements?

    <p>Because they have different performance requirements</p> Signup and view all the answers

    What is the purpose of Random Early Discard (RED) algorithms?

    <p>To discard packets early to avoid congestion</p> Signup and view all the answers

    What is the primary motivation for TCP retransmitting packets?

    <p>To provide packet loss protection</p> Signup and view all the answers

    What is the purpose of the implicit-null label in MPLS?

    <p>To remove the top label of the incoming MPLS packet</p> Signup and view all the answers

    What is the value of the implicit-null label in MPLS?

    <p>3 (20 bit label field)</p> Signup and view all the answers

    What is the purpose of the explicit-null label in MPLS?

    <p>To preserve the EXP value of the top label</p> Signup and view all the answers

    What is the process of removing the top label in the label stack and forwarding the resulting packet?

    <p>Penultimate hop popping</p> Signup and view all the answers

    What is signaled by the downstream Edge LSR during label distribution with LDP?

    <p>Implicit-null label</p> Signup and view all the answers

    What happens to the incoming MPLS packet when the aggregate label is used?

    <p>The packet is converted to an IP packet and an FIB lookup is performed</p> Signup and view all the answers

    What is the purpose of the aggregate label in MPLS?

    <p>To perform an FIB lookup and identify the outgoing interface</p> Signup and view all the answers

    What is the result of penultimate hop popping in MPLS networks?

    <p>The top label is removed and the packet is forwarded</p> Signup and view all the answers

    What is the primary function of routers R1 and R4 in an MPLS enabled network?

    <p>They are the only routers that perform a routing lookup.</p> Signup and view all the answers

    What determines the path in an MPLS network?

    <p>All of the above</p> Signup and view all the answers

    What is the function of Label Switched Paths (LSP) in an MPLS network?

    <p>To define paths between endpoints</p> Signup and view all the answers

    Why are routers R1 and R4 referred to as edge border routers in an MPLS network?

    <p>Because they are the entry and exit points of the MPLS network.</p> Signup and view all the answers

    What happens to a packet when it reaches router R1 in the traditional IP forwarding operation?

    <p>It is forwarded to the appropriate connected interface.</p> Signup and view all the answers

    What is the significance of labels in an MPLS network?

    <p>They have local significance to the router generating them.</p> Signup and view all the answers

    What is the difference between traditional IP forwarding and MPLS forwarding?

    <p>Only edge routers perform a routing lookup in MPLS forwarding.</p> Signup and view all the answers

    What is the advantage of using MPLS forwarding over traditional IP forwarding?

    <p>It allows for more efficient use of network resources.</p> Signup and view all the answers

    What is the primary function of Cisco Express Forwarding (CEF)?

    <p>To enhance the simplicity and IPv4 forwarding performance of a router</p> Signup and view all the answers

    What is the Forwarding Information Base (FIB) responsible for in a Cisco router?

    <p>Maintaining a mapping of destination networks to next-hop adjacencies</p> Signup and view all the answers

    What is an adjacency in the context of a Cisco router?

    <p>A network node that can reach another node with a single hop</p> Signup and view all the answers

    What is responsible for creating entries in the LIB and LFIB?

    <p>The distribution protocol in use between adjacent MPLS neighbors</p> Signup and view all the answers

    Where does the FIB reside in a Cisco router?

    <p>In the data plane</p> Signup and view all the answers

    What is the relationship between FIB table and routing table entries?

    <p>One-to-one</p> Signup and view all the answers

    What are the two other structures maintained in a Cisco router in addition to the FIB?

    <p>LIB and LFIB</p> Signup and view all the answers

    What is stored in the FIB table?

    <p>A mapping of destination networks to next-hop adjacencies</p> Signup and view all the answers

    What is the purpose of the explicit-null label in MPLS?

    <p>To preserve the EXP value of the top label of an incoming packet</p> Signup and view all the answers

    In penultimate hop popping, what does the downstream Edge LSR distribute to the upstream router?

    <p>An implicit-null label</p> Signup and view all the answers

    What is the value of the implicit-null label in a 20-bit label field?

    <p>3</p> Signup and view all the answers

    What happens to an MPLS packet when it is assigned an aggregate label?

    <p>The label stack is removed and an FIB lookup is performed</p> Signup and view all the answers

    What is the primary purpose of using the implicit-null label in MPLS networks?

    <p>To implement penultimate hop popping</p> Signup and view all the answers

    What is the result of removing the top label in the label stack in penultimate hop popping?

    <p>An MPLS packet with the remaining label stack</p> Signup and view all the answers

    What is the primary function of the penultimate hop popping process?

    <p>To remove the top label in the label stack</p> Signup and view all the answers

    What is the purpose of the aggregate label in MPLS networks?

    <p>To perform an FIB lookup to identify the outgoing interface</p> Signup and view all the answers

    What happens to a labeled packet when it traverses an LSR?

    <p>The label TTL value is decremented by 1</p> Signup and view all the answers

    Where is the label inserted in an IP packet?

    <p>Between the Layer 2 and Layer 3 headers</p> Signup and view all the answers

    What is the purpose of the S bit in the label?

    <p>To indicate the end of the label stack</p> Signup and view all the answers

    What happens when an egress Edge LSR encounters the bottom of the label stack?

    <p>It performs a route lookup</p> Signup and view all the answers

    What is the purpose of label stacks in MPLS?

    <p>To implement MPLS-based services</p> Signup and view all the answers

    What does the second label in the label stack identify in MPLS VPN?

    <p>The VPN</p> Signup and view all the answers

    What is the purpose of label imposition in MPLS?

    <p>To add labels to the packet</p> Signup and view all the answers

    What happens to a packet when the TTL value is 0?

    <p>It is discarded</p> Signup and view all the answers

    What is the reason for activating QoS mechanisms to discard traffic?

    <p>To discard traffic that is consistently above the guaranteed minimum bandwidth</p> Signup and view all the answers

    What type of delay can be compensated for by some networking equipment?

    <p>Finite delay</p> Signup and view all the answers

    What is the effect of jitter on real-time applications?

    <p>It has a significant effect</p> Signup and view all the answers

    What is an example of fixed delay in a network?

    <p>Propagation delay</p> Signup and view all the answers

    What is the result of network delay on certain applications?

    <p>They time-out and fail</p> Signup and view all the answers

    What can be used to compensate for network delay in certain applications?

    <p>All of the above</p> Signup and view all the answers

    What is the reason for network delay in a network?

    <p>All of the above</p> Signup and view all the answers

    What is the effect of delay on QoS?

    <p>It has a negative effect</p> Signup and view all the answers

    What is the primary function of the data plane in MPLS?

    <p>To forward labeled packets between routers</p> Signup and view all the answers

    What information does the top label in a label stack identify in MPLS VPN implementations?

    <p>The public IP address of the egress LSR</p> Signup and view all the answers

    What is the purpose of the Forwarding Information Base (FIB) in a Cisco router?

    <p>To make routing decisions based on IP addresses</p> Signup and view all the answers

    What is the primary characteristic of the control plane in MPLS?

    <p>Distributing labels between routers</p> Signup and view all the answers

    What happens to the incoming MPLS packet when it is associated with an untagged outgoing label?

    <p>The label is removed and it is forwarded as an IP packet</p> Signup and view all the answers

    What is responsible for creating entries in the LIB and LFIB?

    <p>CEF</p> Signup and view all the answers

    What is the purpose of liberal label retention mode in MPLS?

    <p>To retain all received labels</p> Signup and view all the answers

    What is the foundation on which MPLS and its services operate on a Cisco router?

    <p>Cisco Express Forwarding</p> Signup and view all the answers

    What is the primary function of MPLS in a network?

    <p>To increase the speed and control the flow of network traffic</p> Signup and view all the answers

    What is the purpose of labels in an MPLS network?

    <p>To direct the packet through a predetermined path</p> Signup and view all the answers

    What is the result of assigning a label to a packet in MPLS?

    <p>The packet is directed through a predetermined path</p> Signup and view all the answers

    What is the primary category of traffic that requires low latency and low jitter?

    <p>Interactive</p> Signup and view all the answers

    What is the purpose of the label stack in MPLS?

    <p>To direct packets through a predetermined path</p> Signup and view all the answers

    What is the primary function of the control plane in MPLS?

    <p>To distribute labels and establish the label-forwarding table</p> Signup and view all the answers

    What is the relationship between the FIB and routing table entries in a Cisco router?

    <p>The FIB is a subset of the routing table</p> Signup and view all the answers

    What is the purpose of the Forwarding Information Base (FIB) in a Cisco router?

    <p>To store the forwarding information for packets</p> Signup and view all the answers

    What is the primary advantage of using MPLS technology?

    <p>To create Virtual Private Networks</p> Signup and view all the answers

    What is the function of MPLS in packet forwarding?

    <p>To forward traffic using labels instead of destination IP addresses</p> Signup and view all the answers

    What is the benefit of MPLS in terms of network infrastructure?

    <p>It provides a single unified network infrastructure</p> Signup and view all the answers

    What is the main advantage of using MPLS VPNs?

    <p>To provide a single network infrastructure for real-time traffic</p> Signup and view all the answers

    What is the purpose of MPLS in next-generation IP-based backbone networks?

    <p>To provide an elegant solution to satisfy the bandwidth management and service requirements</p> Signup and view all the answers

    What is the advantage of MPLS in terms of traffic engineering?

    <p>It provides optimal traffic flow</p> Signup and view all the answers

    What is the role of MPLS in service providers' networks?

    <p>It is used to provide a single network infrastructure for real-time traffic</p> Signup and view all the answers

    What is the innovation utilized by all Internet Service Providers (ISPs) in their core or backbone networks for packet forwarding?

    <p>MPLS 4</p> Signup and view all the answers

    What is the primary function of Cisco Express Forwarding (CEF) on a Cisco router?

    <p>To enhance the simplicity and IPv4 forwarding performance of a router</p> Signup and view all the answers

    What is stored in the Forwarding Information Base (FIB) table?

    <p>A mapping of destination networks in the routing table to appropriate next-hop adjacencies</p> Signup and view all the answers

    What is responsible for creating entries in the LIB and LFIB structures?

    <p>The distribution protocol in use between adjacent MPLS neighbors</p> Signup and view all the answers

    What is an adjacency in the context of a Cisco router?

    <p>A network node that can reach one another with a single hop across the link layer</p> Signup and view all the answers

    Where does the Forwarding Information Base (FIB) reside in a Cisco router?

    <p>In the data plane</p> Signup and view all the answers

    What is the relationship between FIB table and routing table entries?

    <p>There is a one-to-one mapping between FIB table and routing table entries</p> Signup and view all the answers

    What is the function of the Label Forwarding Information Base (LFIB) in a Cisco router?

    <p>To forward labeled packets in the data plane</p> Signup and view all the answers

    What is the primary purpose of the MPLS label stack?

    <p>To forward labeled packets across the network</p> Signup and view all the answers

    What is the path from source to destination for a data packet through an MPLS-enabled network?

    <p>MPLS Label Switched Path (LSP)</p> Signup and view all the answers

    What is the direction of data flow in an MPLS network with respect to a destination network?

    <p>Downstream</p> Signup and view all the answers

    What is the primary function of the control plane in MPLS?

    <p>Label distribution and routing information</p> Signup and view all the answers

    What is the purpose of the Label Distribution Protocol (LDP) in MPLS?

    <p>To distribute labels between LSRs</p> Signup and view all the answers

    What is the label stack in MPLS?

    <p>A stack of labels attached to an IP packet</p> Signup and view all the answers

    What is the function of the Forwarding Information Base (FIB) in a Cisco router?

    <p>To store label table entries</p> Signup and view all the answers

    What is the purpose of the Label Forwarding Information Base (LFIB) in a Cisco router?

    <p>To store label table entries</p> Signup and view all the answers

    What is the concept of upstream and downstream in MPLS?

    <p>Refers to the direction of label distribution in an MPLS network</p> Signup and view all the answers

    What is the purpose of label distribution protocols in MPLS?

    <p>To assign labels to destination networks</p> Signup and view all the answers

    What is the default label distribution protocol on Cisco routers?

    <p>Dependent on the IOS version</p> Signup and view all the answers

    What is the TCP port number used by LDP?

    <p>646</p> Signup and view all the answers

    What happens when the command mpls label protocol is configured?

    <p>The default label distribution protocol is overridden</p> Signup and view all the answers

    What is the effect of configuring the command mpls label protocol in interface configuration mode?

    <p>It overrides the global configuration</p> Signup and view all the answers

    What is the purpose of LDP or TDP in MPLS?

    <p>To exchange labels between adjacent LSRs</p> Signup and view all the answers

    What is the significance of label distribution protocols in MPLS?

    <p>To enable LSRs to learn about labels assigned to destination networks</p> Signup and view all the answers

    What is the relationship between LDP and TDP?

    <p>LDP and TDP function the same way but are not interoperable</p> Signup and view all the answers

    In a scenario where a network operator owns the network connection's infrastructure, what may be an attractive choice to provide QoS?

    <p>Adding bandwidth to provide QoS.</p> Signup and view all the answers

    What is a limitation of some interconnect technologies, such as fixed or mobile wireless?

    <p>Frequency spectrum limitations.</p> Signup and view all the answers

    What can a network operator do to offer service differentiation between premium data services and best-effort subscribers?

    <p>Implement QoS mechanisms.</p> Signup and view all the answers

    What is the benefit of a network operator adding additional wavelengths to provide QoS?

    <p>It increases profit margins.</p> Signup and view all the answers

    What is a scenario where a network operator may not need to increase bandwidth to provide QoS?

    <p>When the network is lightly to moderately loaded.</p> Signup and view all the answers

    What is the advantage of using DWDM interconnect technology over fiber optic connections?

    <p>It allows bandwidth to be added simply and cost-effectively over the existing cable infrastructure.</p> Signup and view all the answers

    What is the result of a network operator offering premium data services with performance guarantees?

    <p>Increased profit margins.</p> Signup and view all the answers

    What is a benefit of a network operator owning the network connection's infrastructure?

    <p>It simplifies the addition of bandwidth to provide QoS.</p> Signup and view all the answers

    When an IP packet is received by the Edge LSR, what operation is performed?

    <p>No lookup is performed in the LIB</p> Signup and view all the answers

    What is the primary goal of achieving end-to-end QoS in a network?

    <p>To ensure network elements apply consistent treatment to traffic flows</p> Signup and view all the answers

    What is a characteristic of network traffic that requires QoS?

    <p>Highly diverse and each type has unique requirements</p> Signup and view all the answers

    What is the result of not implementing QoS in a network with diverse traffic types?

    <p>Applications with different QoS requirements are mixed over a common IP transport network</p> Signup and view all the answers

    What is the primary motivation for creating a QoS-enabled network?

    <p>To provide a holist view of the need for QoS</p> Signup and view all the answers

    What is the relationship between the LIB and the label distribution process?

    <p>The LIB is used to store label mappings for network prefixes</p> Signup and view all the answers

    What is the primary function of the Edge LSR in the context of penultimate hop popping?

    <p>To pop the top label from incoming packets</p> Signup and view all the answers

    What is the benefit of penultimate hop popping in terms of lookup operations?

    <p>It reduces the number of lookup operations in the Edge LSR</p> Signup and view all the answers

    What is the primary reason for network operators to implement redundant interfaces, processor cards, or power supplies in routers and switches?

    <p>To increase the network's availability and reduce downtime</p> Signup and view all the answers

    What is the result of oversubscribing bandwidth on a network?

    <p>The bandwidth a user subscribed to is not always available</p> Signup and view all the answers

    What is the primary goal of implementing QoS technologies in a network?

    <p>To guarantee a certain level of quality of service</p> Signup and view all the answers

    What is the relationship between the availability of a network and the quality of service provided?

    <p>The availability of a network has a direct impact on the quality of service</p> Signup and view all the answers

    What is the primary function of emission priority in QoS?

    <p>To prioritize certain types of traffic over others</p> Signup and view all the answers

    What is the result of a network being unavailable, even for brief periods of time?

    <p>The user or application may achieve unpredictable or undesirable performance</p> Signup and view all the answers

    What is the difference between available bandwidth and guaranteed bandwidth?

    <p>Available bandwidth is the maximum bandwidth available, while guaranteed bandwidth is the minimum bandwidth guaranteed to an application</p> Signup and view all the answers

    What is the primary reason for implementing QoS performance dimensions such as network availability, bandwidth, delay, jitter, and loss?

    <p>To ensure a certain level of quality of service for critical applications</p> Signup and view all the answers

    What is the primary function of the 3-bit experimental field in an MPLS label?

    <p>To assign QoS to the FEC</p> Signup and view all the answers

    What determines the properties of a prefix in an MPLS network?

    <p>The 20-bit label value</p> Signup and view all the answers

    What is the purpose of a label stack in MPLS?

    <p>To specify multiple functions for a single IP packet</p> Signup and view all the answers

    What is identified by the bottom-of-stack indicator?

    <p>The bottom label of the label stack</p> Signup and view all the answers

    What is the label value in an MPLS label?

    <p>A 20-bit number</p> Signup and view all the answers

    What is the purpose of the 8-bit Time-to-Live field in an MPLS label?

    <p>To specify the TTL value for the packet</p> Signup and view all the answers

    How are labels assigned in an MPLS network?

    <p>Per interface or per chassis</p> Signup and view all the answers

    What is the result of multiple labels being imposed on a single IP packet?

    <p>A label stack</p> Signup and view all the answers

    Study Notes

    MPLS Architectural Blocks

    • MPLS functionality is divided into two main architectural blocks:
      • Control plane: performs functions related to identifying reachability to destination prefixes, including Layer 3 routing information and label distribution protocols.
      • Data plane: performs functions related to forwarding data packets, including label imposition and removal.

    Label Imposition and Disposition

    • Labels are inserted between the Frame Header and the Layer 3 Header in an IP packet.
    • The TTL field in the label performs the same function as an IP TTL, preventing looping of unwanted packets in the network.
    • When a labeled packet traverses an LSR, the label TTL value is decremented by 1.
    • An egress Edge LSR continues label disposition in the label stack until it finds the bottom of the stack (S bit set to 1).

    Label Stacks and MPLS Services

    • Label stacks are implemented in MPLS-based services such as MPLS VPN and MPLS traffic engineering.
    • In MPLS VPN, the second label in the label stack identifies the VPN.
    • In traffic engineering, the top label identifies the endpoint of the TE tunnel, and the second label identifies the destination.

    QoS Performance Dimensions

    • Network availability: the summation of the availability of many items used to create a network.
    • Bandwidth: subdivided into available bandwidth and guaranteed bandwidth.
    • Delay: affects the user or application's experience.
    • Jitter: affects the user or application's experience.
    • Loss: affects the user or application's experience.

    Network Availability and Bandwidth

    • Network availability is critical for QoS, and even brief periods of unavailability can affect performance.
    • Bandwidth allocation can be subdivided into available bandwidth and guaranteed bandwidth.
    • Oversubscribing bandwidth can lead to congestion and decreased network performance.

    QoS Requirements for Applications

    • Different applications have varying QoS requirements, which can be mixed over a common IP transport network.
    • Applications such as voice, video conferencing, and others have unique QoS requirements, including low packet loss, minimal delay, and guaranteed bandwidth.

    MPLS Fundamentals

    • The TTL field in MPLS packets serves the same function as IP TTL, preventing looping of unwanted packets in the network by discarding packets when the TTL reaches 0.
    • The label TTL value is decremented by 1 each time a labeled packet traverses an LSR.
    • The label is inserted between the Frame Header and Layer 3 Header in the packet.

    Label Imposition and Label Stack

    • Label imposition occurs when an LSR swaps only the top label in a label stack.
    • The S bit (bottom-of-stack indicator) in the label indicates whether a label stack implementation is in use (0) or not (1).
    • An egress Edge LSR continues label disposition in the label stack until it finds the bottom of the stack (S bit = 1).
    • Label stacks are implemented in MPLS-based services like MPLS VPN and MPLS traffic engineering.

    MPLS Control and Data Plane Components

    • Cisco Express Forwarding (CEF) is a prerequisite for implementing MPLS on Cisco routers.
    • CEF uses a Forwarding Information Base (FIB) for destination switching decisions, which mirrors the entire contents of the IP routing table.
    • The FIB contains a mapping of destination networks to next-hop adjacencies.
    • There are three primary structures in an MPLS router: the FIB, Label Information Base (LIB), and Label Forwarding Information Base (LFIB).

    MPLS Label Retention

    • Liberal label retention mode: an LSR maintains bindings between a label and a destination prefix, even if the downstream LSR is not the next hop.
    • Conservative label retention mode: an LSR discards bindings received from non-next-hop downstream LSRs.

    Special Outgoing Label Types

    • Untagged: incoming MPLS packet is converted to an IP packet and forwarded to the destination (MPLS to IP Domain transition).
    • Implicit-null or POP label: top label is removed, and the resulting packet is forwarded to the next-hop downstream router.
    • Explicit-null Label: preserves the EXP value of the top label and forwards the packet as an MPLS packet to the next-hop downstream router.
    • Aggregate: incoming MPLS packet is converted to an IP packet, and an FIB lookup is performed to identify the outgoing interface to the destination.

    Penultimate Hop Popping

    • Performed in MPLS-based networks where the router upstream to the Edge LSR removes the top label in the label stack and forwards the resulting packet.
    • Signaled by the downstream Edge LSR during label distribution with LDP.

    Congestion Avoidance and QoS

    • Congestion can lead to packet loss, and TCP retransmission can reduce network performance.
    • Congestion avoidance mechanisms like Random Early Discard (RED) can help manage congestion for TCP-based flows.
    • QoS technologies can help ensure predictable behavior for applications with different performance requirements.

    Data Forwarding Path

    • In traditional IP forwarding, routers perform route lookups for each packet and forward it to the next hop router until it reaches its destination
    • In the example network, R4 receives a packet destined for 172.16.10.0 network and forwards it to R3, then R2, then R1, which is directly connected to the destination network

    Overview of MPLS Forwarding

    • In MPLS enabled networks, packets are forwarded based on labels generated by each router
    • Labels correspond to IP destination addresses or other parameters, and define paths called Label Switched Paths (LSP) between endpoints
    • Only edge routers perform routing lookups, while inner routers forward packets based on labels
    • Labels are inserted between the Frame Header and Layer 3 Header in an IP packet

    MPLS Label Imposition and Disposition

    • The TTL field in the label decrements by 1 as the packet traverses each router, and the packet is discarded when the TTL reaches 0
    • If the S bit in the label is 0, it indicates a label stack implementation, and the router swaps only the top label
    • The Edge LSR continues label disposition until it finds the bottom of the label stack, then performs a route lookup based on the IP Layer 3 Header

    MPLS Label Stacks

    • Label stacks are implemented in MPLS VPN and MPLS traffic engineering
    • Each label in the label stack has a specific function, such as identifying the VPN or destination
    • In Layer 2 VPN implementations, the top label identifies the Tunnel Header or endpoint, and the second label identifies the VC

    MPLS Control and Data Plane Components

    • Cisco Express Forwarding (CEF) is the foundation for MPLS and its services on Cisco routers
    • CEF uses a Forwarding Information Base (FIB) for destination switching decisions, which mirrors the IP routing table
    • The FIB contains a mapping of destination networks to next-hop adjacencies

    Special Label Types

    • Implicit-null or POP label: assigned when the top label is removed and the resulting packet is forwarded to the next-hop router
    • Explicit-null Label: preserves the EXP value of the top label and is used in QoS with MPLS
    • Aggregate Label: converts the incoming MPLS packet to an IP packet and performs a FIB lookup to identify the outgoing interface to the destination

    Penultimate Hop Popping

    • Performed in MPLS-based networks where the router upstream to the Edge LSR removes the top label in the label stack and forwards the resulting packet
    • Signaled by the downstream Edge LSR during label distribution with LDP
    • QoS mechanisms may be activated to discard traffic that is consistently above the guaranteed minimum bandwidth

    Delay

    • Network delay is the transit time an application experiences from the ingress point to the egress point of the network
    • Fixed delay examples include applications-based delay, data transmission delay, and propagation delay
    • Variable delay examples include ingress queuing delay, contention with other traffic, and egress queuing delay
    • Delay can cause significant QoS issues with applications such as voice and video

    Jitter

    • Jitter is the measure of delay variation between consecutive packets for a given traffic flow
    • Jitter has a pronounced effect on real-time, delay-sensitive applications such as voice and video

    MPLS Technology and Quality of Service (QoS)

    • MPLS solutions provide flexibility and value-added services, allowing service providers to increase revenue.
    • MPLS is an elegant solution for satisfying bandwidth management and service requirements in next-generation IP-based backbone networks.
    • MPLS technology helps address the challenges of transporting bits and bytes over the backbone to provide differentiated classes of service to users.
    • Class of service (CoS) and QoS issues must be addressed to support diverse network user requirements.

    MPLS Basics

    • MPLS is an IP technology developed by the Internet Engineering Task Force (IETF) that forwards traffic using labels instead of destination IP addresses.
    • MPLS is a technique used by service providers to provide a better, single network infrastructure for real-time traffic such as voice and video.
    • The main advantage of utilizing MPLS is to create Virtual Private Networks (VPNs).
    • MPLS has the capacity to develop both Layer 2 and Layer 3 VPNs.

    MPLS Advantages

    • MPLS provides traffic engineering, utilization of a unified network infrastructure, optimal traffic flow, and better IP over ATM integration.
    • MPLS is used by all Internet Service Providers (ISPs) in their core or backbone networks for packet forwarding.

    MPLS Learning Objectives

    • Unicast IP forwarding in traditional IP networks
    • Architectural blocks of MPLS
    • MPLS terminology
    • CEF, FIB, LFIB, and LIB
    • MPLS label assignment
    • MPLS LDP session establishment
    • MPLS label distribution and retention
    • Penultimate hop popping
    • Frame-mode MPLS operation and loop prevention
    • Cell-mode MPLS operation, VC-merge, cell interleaving, and loop prevention
    • Quality of Service (QoS) parameters

    MPLS and QoS

    • MPLS has evolved as a solution to address speed, scalability, QoS management, and traffic engineering challenges in present-day networks.
    • MPLS assigns a label to each packet to send it along a predetermined path, increasing the speed and control of network traffic.
    • MPLS is data forwarding technology that increases the speed and controls the flow of network traffic.

    MPLS Label Switched Path (LSP)

    • MPLS LSP is the path from source to destination for a data packet through an MPLS-enabled network.
    • LSPs are unidirectional in nature.
    • The LSP is usually derived from IGP routing information but can diverge from the IGP's preferred path to the destination.

    MPLS Control and Data Plane Components

    • Cisco Express Forwarding (CEF) is the foundation on which MPLS and its services operate on a Cisco router.
    • CEF is a prerequisite to implement MPLS on all Cisco platforms except traditional ATM switches.
    • CEF uses a Forwarding Information Base (FIB) for destination switching decisions, which mirrors the entire contents of the IP routing table.
    • When CEF is used on a router, the router maintains an FIB, which contains a mapping of destination networks in the routing table to appropriate next-hop adjacencies.
    • The Label Information Base (LIB) and Label Forwarding Information Base (LFIB) are maintained on the router, and the distribution protocol in use between adjacent MPLS neighbors is responsible for creating entries in the LIB and LFIB.

    MPLS Technology Overview

    • An MPLS label is a 20-bit number assigned to a destination prefix on a router, defining the properties of the prefix and forwarding mechanisms for a packet.
    • An MPLS label consists of:
      • 20-bit label value
      • 3-bit experimental field
      • 1-bit bottom-of-stack indicator
      • 8-bit Time-to-Live (TTL) field

    MPLS Label Assignment

    • A label is assigned to IP networks reachable by a router and then imposed on data packets forwarded to those IP networks.
    • Labels can be assigned either globally (per router) or per interface on a router.
    • Label distribution protocol (LDP or TDP) assigns and exchanges labels between adjacent LSRs in an MPLS domain.

    LDP Session Establishment

    • LDP is the default label distribution protocol.
    • TDP is deprecated and not interoperable with LDP.
    • The command mpls label protocol {ldp | tdp} is configured only if LDP is not the default label distribution protocol or if reverting from LDP to TDP.

    Penultimate Hop Popping

    • Penultimate hop popping saves a single lookup on edge routers.
    • The operation of penultimate hop popping is depicted in Figure 22.

    Quality of Service (QoS)

    • QoS is a broad term used to describe the overall experience a user or application will receive over a network.
    • QoS involves a broad range of technologies, architectures, and protocols.
    • Network operators achieve end-to-end QoS by ensuring that network elements apply consistent treatment to traffic flows as they traverse the network.

    Importance of QoS

    • Network traffic is highly diverse, and each traffic type has unique requirements in terms of bandwidth, delay, jitter, and availability.
    • QoS is important because it ensures that network traffic meets the required performance objectives.

    Bandwidth Owner versus Renter

    • If the network operator owns the network connection, adding bandwidth to provide QoS may be an attractive choice.
    • Some interconnect technologies, such as DWDM, allow bandwidth to be added simply and cost-effectively over the existing cable infrastructure.

    QoS Performance Dimensions

    • QoS parameters can be measured and monitored to determine whether a service level is being achieved.
    • These parameters include:
      • Network Availability
      • Bandwidth
      • Delay
      • Jitter
      • Loss
    • QoS performance-affecting parameters that cannot be measured include:
      • Emission priority
      • Discard priority

    Network Availability

    • Network availability can have a significant impact on QoS.
    • Network availability is the summation of the availability of many items that are used to create a network, including:
      • Networking device redundancy
      • Resilient networking protocols
      • Multiple physical connections
      • Backup power sources

    Bandwidth

    • Bandwidth is the second most significant parameter that affects QoS.
    • Bandwidth allocation can be subdivided into two types:
      • Available Bandwidth
      • Guaranteed Bandwidth

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    Description

    This quiz covers the architectural blocks of MPLS, including the control plane and data plane, and their functions in Cisco devices. It also touches on label removal and packet forwarding in MPLS networks.

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