Networking Switch Fabric and Forwarding Tables
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Questions and Answers

What is the primary function of the interconnection or crossbar network in a switching plane?

  • To provide a high-speed connection between input and output ports.
  • To control the flow of data packets between fabric planes.
  • To handle the storage and buffering of datagrams before transmission.
  • To route datagrams to their destination based on the destination address. (correct)

    • What is the potential issue associated with input port queuing when the fabric is slower than the combined input ports?

  • The fabric may experience high latency as a result of increased queue lengths.
  • The input ports may become a bottleneck, preventing other datagrams from entering the switch fabric.
  • The interconnection network can become overloaded and fail to route datagrams efficiently.
  • Datagrams may be dropped due to input buffer overflow. (correct)

    • What is the primary function of a switch fabric?

  • To manage the interconnection of multiple network devices.
  • To control the flow of data between input and output ports.
  • To detect and correct errors in data packets. (correct)
  • To buffer and forward datagrams to their next destination.

    • What is the main reason for using a "drop policy" at the output buffer in output port queuing?

    <p>To prevent the output buffer from becoming overloaded and dropping datagrams. (C)</p> Signup and view all the answers

    What is the purpose of longest prefix matching in a forwarding table?

    <p>It ensures that the correct interface is used for routing a packet to its destination. (A)</p> Signup and view all the answers

    Which of the following forwarding table entries would be used for a destination address of 11001000 00010111 00010110 10100001?

    <p>11001000 00010111 00010110 10100001 0 (C)</p> Signup and view all the answers

    Which of the following forwarding table entries would be used for a destination address with the prefix 11001000 00010111 00011000?

    <p>11001000 00010111 00011000 ******** 1 (C)</p> Signup and view all the answers

    What is the benefit of using a forwarding table that implements longest prefix matching?

    <p>It allows for more efficient packet forwarding. (D)</p> Signup and view all the answers

    Which of the following is an advantage of using longest prefix matching in a forwarding table?

    <p>It improves the performance of the network. (B)</p> Signup and view all the answers

    Consider a forwarding table with the following entries: 11001000 00010111 00010*** ******** 0 11001000 00010111 00011*** ******** 2 otherwise * 3 Which interface would be selected for a destination address of 11001000 00010111 00011001?

    <p>2 (B)</p> Signup and view all the answers

    In the context of longest prefix matching, what does the term "prefix" refer to?

    <p>A set of bits in an IP address that are used to identify a network (D)</p> Signup and view all the answers

    What is the primary purpose of a forwarding table in a network?

    <p>Determine the best path for packets to reach their destination (B)</p> Signup and view all the answers

    What is the purpose of the DHCP Discover message sent by the client?

    <p>To announce the client's presence to the network and request an IP address (C)</p> Signup and view all the answers

    What does 'yiaddr' refer to in the DHCP process?

    <p>The client's assigned IP address (A)</p> Signup and view all the answers

    Why might a client receive DHCP offers from multiple DHCP servers?

    <p>There may be multiple DHCP servers on the network offering different IP addresses (B)</p> Signup and view all the answers

    What information is transmitted in the DHCP Offer message by the server?

    <p>The IP address, subnet mask, and default gateway address the client can use (C)</p> Signup and view all the answers

    What is the purpose of the DHCP Request message sent by the client?

    <p>To confirm the client's acceptance of the offered configuration (C)</p> Signup and view all the answers

    What is the role of the DHCP ACK message sent by the server?

    <p>To confirm that the client has successfully been assigned an IP address (A)</p> Signup and view all the answers

    Why is the DHCP process considered a four-step process?

    <p>The process involves four distinct phases of configuration and negotiation (B)</p> Signup and view all the answers

    What is the purpose of the transaction ID in the DHCP messages?

    <p>To identify the specific client requesting an IP address (B)</p> Signup and view all the answers

    What does generalized forwarding allow a packet switch to do?

    <p>Drop, modify, or log packets based on header fields (C)</p> Signup and view all the answers

    What is the purpose of a remote controller in generalized forwarding?

    <p>Computing and distributing match-plus-action flow tables for the packet switch (C)</p> Signup and view all the answers

    What is the main concept behind the "match-plus-action" forwarding abstraction?

    <p>Matching incoming packets with specific rules and triggering corresponding actions based on those rules (A)</p> Signup and view all the answers

    What is the name of the standard rule that generalized forwarding is based on?

    <p>OpenFlow (B)</p> Signup and view all the answers

    What is a defining characteristic of OpenFlow 1.0?

    <p>It introduced key SDN abstractions including the match-plus-action model (C)</p> Signup and view all the answers

    What is the primary goal of DHCP?

    <p>To provide a mechanism for hosts to dynamically obtain IP addresses from a server. (C)</p> Signup and view all the answers

    What makes DHCP a plug-and-play protocol?

    <p>It simplifies network management and makes it easier for new devices to join. (B)</p> Signup and view all the answers

    What is the destination IP address used in the DHCP Discover message by a new host requesting an IP address?

    <p>255.255.255.255 (A)</p> Signup and view all the answers

    In the DHCP 4-step process, what does the client do in the DHCP Request message?

    <p>Requests a specific IP address offered by a DHCP server. (D)</p> Signup and view all the answers

    Besides an IP address, what other information can a DHCP server provide to a client?

    <p>The IP address of the default gateway, the name and IP address of DNS server, and the network mask. (A)</p> Signup and view all the answers

    What is the purpose of the DHCP ACK message?

    <p>To inform the DHCP server that the client has successfully obtained an IP address. (D)</p> Signup and view all the answers

    Which of the following is NOT a benefit of DHCP?

    <p>It increases security by requiring manual IP address configuration for each device. (C)</p> Signup and view all the answers

    What would be the impact of a DHCP server malfunctioning on a network?

    <p>It would inhibit new devices from joining the network and potentially disrupt existing connections. (C)</p> Signup and view all the answers

    What is the network address of subnet 2?

    <p>192.168.1.128 (A)</p> Signup and view all the answers

    What is the broadcast address of subnet 0?

    <p>192.168.1.63 (A)</p> Signup and view all the answers

    What is the subnet mask for each subnet after dividing the network?

    <p>255.255.255.192 (A)</p> Signup and view all the answers

    How many bits are borrowed from the host portion to create 4 subnets?

    <p>2 (D)</p> Signup and view all the answers

    What is the range of usable IP addresses for subnet 1?

    <p>192.168.1.65 - 192.168.1.126 (D)</p> Signup and view all the answers

    What is the subnet mask in binary for the subnet 2?

    <p>11111111.11111111.11111111.10000000 (A)</p> Signup and view all the answers

    Why was the original network 192.168.1.0/24 divided into 4 subnets?

    <p>To improve security by isolating different departments (D)</p> Signup and view all the answers

    What is the maximum number of hosts that can be used in each subnet?

    <p>62 (D)</p> Signup and view all the answers

    What is the network address of subnet 1 in binary?

    <p>11000000.10101000.00000001.01000000 (A)</p> Signup and view all the answers

    What is the first host address for subnet 3?

    <p>192.168.1.193 (A)</p> Signup and view all the answers

    Flashcards

    Longest Prefix Match

    A method used to select the longest matching prefix from a forwarding table for routing.

    Forwarding Table

    A table used in routers that maps destination addresses to link interfaces.

    Destination Address

    The address of a target device where data packets are sent.

    Prefix

    A sequence of bits at the start of an address that identifies a subset of addresses.

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    Matching Process

    The steps taken to find the longest prefix that corresponds to a destination address.

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    Binary Addressing

    Using binary digits (0s and 1s) to represent network addresses.

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    Link Interface

    A connection point that routes packets to the appropriate destination based on the prefix match.

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    Routing Decision

    The process by which a router determines the best path for data to reach its destination.

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    Switching Capacity

    The maximum data transfer rate of a switch, measured in Terabits per second (Tbps).

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    Head-of-the-Line (HOL) Blocking

    A situation where the first packet in a queue prevents subsequent packets from moving forward, causing potential delays.

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    Input Port Queuing

    Occurs when the combined traffic from multiple input ports exceeds the switch's fabric speed, leading to delayed processing and possible overflow.

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    Output Port Contention

    A scenario where multiple packets compete for the same output port, leading to possible delays or dropped packets.

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    Drop Policy

    The strategy used by a switch to decide which datagrams to discard when the buffers are full.

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    Subnet

    A subnet is a segmented piece of a larger network, created to improve performance and security.

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    IP Address

    A unique identifier for a device on a network, usually written in decimal format (e.g., 192.168.1.1).

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    Subnet Mask

    A mask that separates the network portion and host portion of an IP address, dictating how many bits are for each.

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    CIDR Notation

    Classless Inter-Domain Routing notation showing the number of bits used for the network, e.g., /24.

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    Network Address

    The first address in a subnet, used to identify the subnet itself rather than a specific device.

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    Broadcast Address

    The last address in a subnet that sends data to all possible hosts within that subnet.

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    Host Portion

    The part of the IP address that identifies a specific device on the network.

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    Borrowing Bits

    Taking bits from the host portion to create more subnets from a single network address.

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    Subnet Size

    Determined by the subnet mask, indicating how many usable addresses are in the subnet.

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    First Host Address

    The first usable address in a subnet, often immediately after the network address.

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    Generalized Forwarding

    A network forwarding method using a match-plus-action flow table managed by a controller.

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    Match-Plus-Action

    An abstraction in networking where a matching rule determines the action taken on a packet.

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    Flow Table

    A table in packet switches that defines how incoming packets should be treated based on matches.

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    OpenFlow

    A standard protocol that facilitates communication between a controller and network devices through match-plus-action rules.

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    Remote Controller

    A central entity that computes and distributes flow tables to packet switches in a network.

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    DHCP

    Dynamic Host Configuration Protocol that allocates IP addresses to hosts dynamically.

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    IP address leasing

    The process where a host temporarily obtains an IP address from a DHCP server.

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    DHCP four-step process

    The sequence of messages: Discover, Offer, Request, and ACK in DHCP.

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    DHCP discover message

    A broadcast message sent by a client to find available DHCP servers.

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    DHCP offer message

    A response from the DHCP server offering an IP address to the client.

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    DHCP request message

    A message sent by the client to request the offered IP address.

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    DHCP ACK message

    The final message from the DHCP server confirming the IP address allocation.

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    Advantages of DHCP

    Simplifies network administration and supports mobile user connectivity.

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    DHCP Discover

    A broadcast message sent by a client to discover available DHCP servers.

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    DHCP Offer

    A message from a DHCP server containing an available IP address and network settings.

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    DHCP Request

    A message sent by the client to accept a specific DHCP offer.

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    DHCP ACK

    Acknowledgment message from the DHCP server confirming the client's request.

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    Transaction ID

    A unique identifier for each DHCP transaction between client and server.

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    yiaddr

    Your IP address in the DHCP exchange process, provided in offers and acknowledgments.

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    Lifetime

    The duration for which the leased IP address is valid, typically measured in seconds.

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    Study Notes

    Chapter 4: Network Layer: The Data Plane

    • This chapter focuses on the data plane of the network layer, focusing on how data is moved through a network.
    • The chapter will cover network layer service models, forwarding versus routing, how a router works, addressing, and generalized forwarding.
    • The implementation of the IP protocol and NAT in the Internet will also be discussed.
    • The chapter will also cover generalized forwarding and SDN.

    Goals

    • Understanding principles behind network layer services, specifically the data plane.
    • Identifying various network layer service models.
    • Differentiating between forwarding and routing processes.
    • Explaining the router's working mechanism.
    • Discussing addressing schemes.
    • Covering generalized forwarding methods involved in transferring data between routers.
    • Providing implementation examples in the Internet.
    • Explaining the IP protocol to understand the datagram format, fragmentation, IPv4 addressing, network address translation (NAT), and IPv6.
    • Explaining various components involved in forwarding data within a router, including input ports, output ports, the switching fabric, and the routing processor.

    Network Layer Services and Protocols

    • The network layer is responsible for transporting segments from the sender to the receiver.
    • The sender encapsulates segments into datagrams, which are passed to the link layer.
    • The receiver delivers segments to the transport layer.
    • This layer involves protocols relevant in every Internet device, such as hosts and routers.
    • Routers examine header fields in IP datagrams to determine the appropriate output ports for forwarding data.

    Two Key Network-Layer Functions

    • Forwarding: The process of moving packets from a router's input to its appropriate output. This process gets the packet through a single interchange.
    • Routing: The process of determining the route a packet takes from source to destination. Routing algorithms are used to make these decisions.
    • Both forwarding and routing work together, with routing algorithms determining forwarding table entries in routers.

    Two Control-Plane Approaches

    • Traditional routing algorithms control how data flows. These algorithms are implemented in the router itself
    • SDN (software-defined networking) uses a remote controller to control routing decisions. This controller computes and installs forwarding tables in routers.

    Network Service Model

    • Question: What service model for transporting datagrams from sender to receiver?
    • Example: Guaranteed delivery, guaranteed delivery with low delay, in-order datagram delivery.
    • Example Services for a flow of datagrams: guaranteed minimum bandwidth to the flow, constraints on changes in inter-packet spacing.

    Network Layer Service Models (QoS Guarantees)

    • Quality of Service (QoS) Guarantees
    • Bandwidth
    • Loss
    • Order
    • Timing
    • Congestion
    • Internet: best effort, no guarantees.
    • ATM (Asynchronous Transfer Mode): Various service models with different QoS guarantees (CBR, VBR, ABR, UBR)

    Network Layer: Data Plane and Control Plane

    • Data plane: The forwarding function determines how a datagram arriving at a router's input port is forwarded to the appropriate output port. This function is local and performed at each router.
    • Control plane: The routing function determines the route taken by datagrams among routers to go from source to destination. This function is network-wide rather than local.

    IP Datagram Format

    • 32 bits: IP datagram is structured as series of fields (version, header length, type of service, datagram length, etc...)

    IP Fragmentation/Reassembly

    • Network links have a maximum transmission unit (MTU) for datagrams.
    • Datagrams larger than the MTU are fragmented into smaller datagrams.
    • Datagrams are reassembled at the destination.
    • Header bits in IP datagrams are used for identifying and ordering fragments.

    Switching Fabrics

    • Transferring packets from input to output links.
    • Measured as a multiple of input/output line rate.
    • Three types, Memory, Bus, and Crosbar.

    Switching via Memory, Bus, and Interconnection Network

    • Switching via memory is the first generation method, but limited by memory bandwidth.
    • Switching via a bus is a better method but can experience contention, which limits bandwidth.
    • Switching via an interconnection network (crossbar) overcomes bandwidth limitations by using multiple switching planes in parallel.

    Input/Output Port Queueing

    • Input port queueing refers to datagrams arriving at a router input port faster than the amount of data being forwarded by the router to the next link.
    • Output port contention arises from output ports being slower than the input port(s).

    How Much Buffering

    • RFC 3439: An average rule of thumb to determine how much buffering is needed.
    • More recent recommendations for buffering equal to RTT*C/N.

    Router Architecture Overview

    • Two key router functions:
    • running routing algorithms/protocols
    • forwarding datagrams.
    • Four router components:
    • input ports
    • output ports
    • switching fabric
    • routing processor

    Input Port Functions

    • Physical layer (bit-level reception).
    • Data link layer (e.g., Ethernet reception).
    • Decentralized Switching.
    • Lookup output port using a forwarding table in input port memory to forward destination based or generalized forwarding (SDNs).

    Destination-Based Forwarding

    • Uses forwarding tables to determine the output interface for a packet based on the destination address.

    Longest Prefix Matching

    • When looking for an entry in the forwarding table, use the longest address prefix that matches the destination address.

    Content Addressable Memory (CAM)

    • An approach to look up an address in forwarding table (fast lookup operation).

    IPv4 Addressing and Subnetting

    • IP addresses are used to identify hosts in networks.
    • They are typically written in dotted decimal notation. Each part of the IP address is represented by a 8 bits number.
    • Subnetting is the process of dividing a network into multiple subnetworks.
    • Subnet masks are used to divide an IP address into network and host portions.
    • Understanding how to determine network address, broadcast address, usable IP addresses is essential.

    Classful Addressing

    • Various class systems (A, B, C, D, E) had different structures separating IP addresses into network and host portions.

    Classless Inter-Domain Routing (CIDR)

    • More flexible than classful addressing.
    • Subnet portion of an IP address can be of arbitrary length.
    • Addresses are arranged as network portion followed by host portion.

    DHCP (Dynamic Host Configuration Protocol)

    • Automatically assigns IP addresses to hosts on a network.
    • Supports network mobility, and simplifies administrator’s work.
    • A four-step process: discover, offer, request, and acknowledge(ACK).

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    Related Documents

    Chapter 4 Network Layer: The Data Plane PDF

    Description

    This quiz explores key concepts related to networking switch fabrics and the function of forwarding tables, specifically focusing on longest prefix matching. It will test your understanding of switching planes, input port queuing issues, and output buffer drop policies. Perfect for students studying network architecture and design.

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