Networking Concepts Quiz
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Questions and Answers

What is the primary function of the network layer?

  • To display data to the user.
  • To maintain user sessions.
  • To move packets from one router to another. (correct)
  • To handle data encryption.

    • What is the process of determining the route packets will take from source to destination called?

  • Encapsulation
  • Segmentation
  • Routing (correct)
  • Forwarding

    • In the context of datagrams, what does encapsulation refer to?

  • Storing data in the physical layer.
  • Removing headers from packets.
  • Displaying data to the application layer.
  • Adding headers to segments. (correct)

    • Which layer does the network layer primarily communicate with to send data to the receiving host?

    <p>Transport layer</p> Signup and view all the answers

    What do routers primarily examine in IP datagrams?

    <p>Header fields</p> Signup and view all the answers

    Which routing method involves sending data to multiple destinations simultaneously?

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

    What does a BGP message contain in relation to routing?

    <p>Prefixes and attributes like AS-PATH and NEXT-HOP</p> Signup and view all the answers

    When a router receives multiple routes for the same prefix, how does it determine which one to select?

    <p>By selecting the route with the shortest AS-PATH</p> Signup and view all the answers

    What attribute of a route is used for finding the best intra-route to a BGP route?

    <p>NEXT-HOP attribute</p> Signup and view all the answers

    In the case of a tie when selecting among routes with equal AS-PATH lengths, what should the router do?

    <p>Use local preference to make a decision</p> Signup and view all the answers

    What does the NEXT-HOP attribute specify in a BGP route?

    <p>The IP address of the router interface that begins the AS PATH</p> Signup and view all the answers

    What happens when the nth set of datagrams arrives at the nth router?

    <p>The router discards datagrams and sends source ICMP messages.</p> Signup and view all the answers

    What does the ICMP message type 3, code 3 indicate?

    <p>Port unreachable.</p> Signup and view all the answers

    What does the NAT translation table store?

    <p>Both source IP address and port number to NAT IP address and new port number pairs</p> Signup and view all the answers

    What is the primary motivation for the development of IPv6?

    <p>To resolve the exhaustion of 32-bit address space.</p> Signup and view all the answers

    What is the role of NAT when processing incoming datagrams?

    <p>It replaces the NAT IP address with the corresponding source IP address from the NAT table</p> Signup and view all the answers

    What is a key feature of the IPv6 datagram format?

    <p>It has a fixed-length 40 byte header.</p> Signup and view all the answers

    Which field is used to identify the upper layer protocol for data in an IPv6 datagram?

    <p>Next header.</p> Signup and view all the answers

    How many simultaneous connections can a single LAN-side address support with a 16-bit port number field?

    <p>60,000</p> Signup and view all the answers

    What is the first step NAT takes in changing a datagram?

    <p>Changing the source address from LAN-side to WAN-side</p> Signup and view all the answers

    What change was made to the checksum in IPv6 compared to IPv4?

    <p>It was removed entirely.</p> Signup and view all the answers

    What is one function of ICMPv6 compared to ICMP in IPv4?

    <p>It includes multicast group management functions.</p> Signup and view all the answers

    Which components does the NAT router add to the NAT translation table during a translation?

    <p>Both source IP and port, and destination NAT IP and port</p> Signup and view all the answers

    When a reply arrives, what does the NAT router change in the datagram's destination address?

    <p>It changes the NAT IP address to the corresponding source IP address</p> Signup and view all the answers

    What does the term 'mixed IPv4 and IPv6 routers' refer to?

    <p>Some routers use IPv4 while others use IPv6.</p> Signup and view all the answers

    What is indicated by the priority field in an IPv6 datagram?

    <p>The urgency of packet delivery.</p> Signup and view all the answers

    What is implied by the need to update the NAT translation table?

    <p>Maintaining the state of each connection requires tracking</p> Signup and view all the answers

    What issue arises from not upgrading all routers to IPv6 at once?

    <p>Challenges in network operation.</p> Signup and view all the answers

    What happens when an outgoing datagram is sent to a non-existent NAT IP address?

    <p>The datagram is lost and not delivered</p> Signup and view all the answers

    What type of address does NAT replace in the destination fields upon receiving incoming datagrams?

    <p>NAT IP address and new port number</p> Signup and view all the answers

    What does RIP stand for?

    <p>Routing Information Protocol</p> Signup and view all the answers

    What is the maximum number of hops allowed in RIP?

    <p>15 hops</p> Signup and view all the answers

    Which of the following is a feature of distance vector algorithms like RIP?

    <p>Relies on advertisements sent out every 30 seconds</p> Signup and view all the answers

    Which routing protocol is classified as an interior gateway protocol (IGP)?

    <p>Open Shortest Path First (OSPF)</p> Signup and view all the answers

    What is typically exchanged in RIP advertisements?

    <p>Up to 25 destination subnets</p> Signup and view all the answers

    What kind of algorithm does RIP utilize for determining routes?

    <p>Distance Vector Algorithm</p> Signup and view all the answers

    How often does RIP send out routing information to neighbors?

    <p>Every 30 seconds</p> Signup and view all the answers

    What is meant by the term 'intra-AS routing'?

    <p>Routing within a single autonomous system</p> Signup and view all the answers

    Which of the following is NOT a commonly used interior gateway protocol?

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

    What metric does RIP primarily use to determine the 'cost' of a path?

    <p>Number of hops</p> Signup and view all the answers

    Study Notes

    Introduction to Computer Networking

    • Chapter 4, Network Layer, 6th edition by Kurose and Ross, Addison-Wesley, March 2012
    • Note on use of slides: slides freely available for all users; Users are permitted to adapt and modify the slides but must cite the source and copyright of the slides.

    Chapter 4: Network Layer

    • Chapter goals: understand principles behind network layer services, including network layer service models, forwarding and routing, how routers work, routing (path selection), broadcast, multicast, instantiation, and implementation in the Internet.
    • 4.1 Introduction
    • 4.2 Virtual Circuit and Datagram Networks
    • 4.3 What's inside a router
    • 4.4 IP: Internet Protocol
      • Datagram format
      • IPv4 addressing
      • ICMP
      • IPv6
    • 4.5 Routing Algorithms
      • Link state
      • Distance vector
      • Hierarchical routing
    • 4.6 Routing in the Internet
      • RIP
      • OSPF
      • BGP
    • 4.7 Broadcast and Multicast Routing

    Network Layer Functions

    • Forwarding: moves packets from a router's input to the appropriate router output
    • Routing: determines the route taken by packets from source to destination
    • Routing Algorithms
    • Interplay between Routing and Forwarding: Routing algorithm determines the end-to-end path through the network, while the forwarding table determines local forwarding at the router
    • Connection Setup: 3rd important function in some network architectures (ATM, frame relay, X.25) involves routers establishing virtual connections before datagrams flow.
    • Network vs. Transport Layer Connection Service:
      • Network layer: between two hosts (may involve intervening routers in the case of virtual circuits)
      • Transport Layer: between two processes
    • Network Service Model:
      • Example services for individual datagrams: guaranteed delivery, guaranteed delivery with less than 40 msec delay
      • Example services for a flow of datagrams: in-order datagram delivery, guaranteed minimum bandwidth, restrictions on changes in inter-packet spacing
    • Virtual Circuits:
      • Behavior similar to a telephone circuit
      • Call setup and teardown for each call
      • Each packet carries a VC identifier (instead of destination address)
      • Routers maintain "state" for each passing connection
      • Dedicated resources are allocated to the VC for predictable service
    • Virtual Circuit Implementation:
      • Path from source to destination
      • VC numbers (one for each link along path)
      • Entries in forwarding tables in routers along the path
    • Datagram Networks:
      • No call setup at network layer
      • No network-level concept of a connection
      • Packets are forwarded using the destination host address
    • Datagram Forwarding Table:
      • To deal with the sheer number of IP addresses, use ranges rather than listing each individual IP.
    • Longest Prefix Matching:
      • Using IP destination address to find best matching in local forwarding table (longest prefix matching)
    • Datagram or VC Network: Why?
      • Internet (datagram): data exchange, elastic service, many link types
      • ATM (VC): evolved from telephony, strict timing, reliability, need for guaranteed service, dumb end systems
    • Router Architecture Overview:
      • two main functions: execute routing algorithms and forward datagrams from incoming to outgoing links
      • Has a routing processing and forwarding data plane
    • Input Port Functions:
      • Decentralized switching
      • Goal: complete input port processing at “line speed”
      • Queuing: for when datagrams arrive faster than forwarding rate into fabric
    • Switching Fabrics: memory, bus, crossbar
    • Three types: memory, bus, crossbar
    • Switching via Memory
    • Switching via a Bus
    • Switching via Interconnection Network
    • Output Ports:
      • Buffering required from fabric's speed to the output line.
      • Scheduling datagrams
    • Input Port Queuing
    • How much buffering? (RFC 3439) for links with typical RTT.
    • Interplay between routing and forwarding
    • Graph abstraction: utility for network contexts (e.g., P2P)
    • Graph Abstraction: costs of link(x,x')
    • Routing Algorithm Classification:
      • Global vs. Decentralized:
        • Global: all routers have complete topology, link cost info
        • Decentralized: routers know physically connected neighbors, link costs to neighbors. Iterative process exchanging information with neighbors.
      • Static vs. Dynamic:
        • Static: routes change slowly over time
        • Dynamic: routes change more quickly, have periodic updates, and in response to link cost changes
    • Dijkstra's Algorithm:
      • Notation: introducing variables for link cost, current value of cost, predecessor node.
      • Initialization: steps for initializing the algorithm
      • Loop: steps for iteratively finding shortest paths
    • Dijkstra's Algorithm: example with resulting shortest-path tree from u and forwarding table.
    • Dijkstra's Algorithm, discussion:
    • Distance Vector Algorithm
      • Bellman-Ford equation (dynamic programming)
      • Introducing cost of path from x-to-y
      • The node achieving minimum is the next hop used in forwarding table
    • Distance Vector Algorithm:
      • defining Dx(y) = estimate of least cost from x-to-y .
    • Distance Vector Algorithm: key idea
    • Distance vector algorithm, iterative, asynchronous with each node
    • Distance vector algorithm, distributed
    • Distance vector algorithm, link cost changes
    • Inter-AS routing protocols, and BGP
    • BGP: Border Gateway Protocol, the de facto inter-domain routing protocol, glue that holds the Internet together
    • BGP protocols
      • eBGP: to get subnet from neighboring ASs
      • iBGP: propagate info to all AS-internal routers
    • BGP route selection
    • Router may learn about more than one route to a destination AS; selects route based on 4 criteria: local preference attribute, shortest AS path, closest NEXT-HOP router, and other criteria.
    • BGP messages
    • Putting it Altogether: How Does an Entry Get Into a Router's Forwarding Table?
    • How does entry get in forwarding table?
    • Router identifies port for route
    • Hot Potato Routing
    • BGP Routing policy
    • Why different intra and Inter-AS routing?

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    Chapter 4 Network Layer PDF

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    Test your understanding of the network layer and routing protocols in this quiz. Explore important concepts such as encapsulation, BGP messages, and route selection. Perfect for students studying computer networking.

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