Network Layer Functions and Protocols Quiz

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Questions and Answers

What is the primary function of forwarding in the network layer?

To evaluate network performance metrics

To plan the trip from source to destination

To encrypt data for security during transmission

To move packets from router’s input to an appropriate router output (correct)

What does routing determine in the context of network layer operations?

The route taken by packets from source to destination (correct)

The format for encapsulating data within datagrams

The specific IP address assigned to a host

The process of managing data link layers

Which of the following best describes what a router does with IP datagrams?

It generates new IP datagrams for each session.

It examines header fields in all IP datagrams passing through it. (correct)

It prioritizes traffic based on application type.

It encrypts them for secure transmission.

Which protocol is part of routing in the Internet?

BGP Signup and view all the answers

What is a characteristic of a connectionless service in networking?

Packets are routed independently without a predefined path Signup and view all the answers

What determines the end-to-end path through a network?

Routing algorithm Signup and view all the answers

What does VC stand for in the context of network services?

Virtual Circuit Signup and view all the answers

What does a forwarding table determine?

Local forwarding at the router Signup and view all the answers

Which of the following ATM classes does not guarantee any bandwidth?

ATM UBR Signup and view all the answers

In which architectures is connection setup an important function?

ATM, frame relay, and X.25 Signup and view all the answers

What happens in the virtual circuit implementation before data can flow?

A call setup and teardown process occurs. Signup and view all the answers

How does the network layer differ from the transport layer in terms of connection service?

Network layer establishes connections between two hosts possibly with intervening routers Signup and view all the answers

In a datagram network, how are packets identified?

Each packet carries a destination host address Signup and view all the answers

Which of the following describes a service model allowing for guaranteed delivery?

Guaranteed delivery with less than 40 msec delay Signup and view all the answers

Which routing algorithm focuses on the complete view of the network?

Link state routing Signup and view all the answers

What is one type of restriction mentioned for network service models?

Restrictions on changes in inter-packet spacing Signup and view all the answers

Which characteristic differentiates connection-oriented services from connectionless services?

Connection-oriented services require dedicated paths. Signup and view all the answers

What value in the arriving packet's header would lead to the output link '1' in local forwarding?

1001 Signup and view all the answers

What type of service does ATM ABR provide?

Guaranteed minimum bandwidth Signup and view all the answers

What is the primary function of the Internet network layer?

Path selection Signup and view all the answers

Which of the following is NOT a routing protocol mentioned?

SMTP Signup and view all the answers

What does IP in the context of the network layer stand for?

Internet Protocol Signup and view all the answers

What does ICMP stand for in networking?

Internet Control Message Protocol Signup and view all the answers

The datagram format in IP includes which of the following?

Protocol version Signup and view all the answers

Which protocol is used for hierarchical routing?

OSPF Signup and view all the answers

Which layer handles the forwarding process in networking?

Network layer Signup and view all the answers

What is the primary role of routing algorithms in a network?

Path selection Signup and view all the answers

Which of the following is a characteristic of 'link state' routing?

Forwarding based on entire network topology Signup and view all the answers

Study Notes

Chapter 4: Network Layer

The slides are freely available to faculty, students, and readers.
The PowerPoint slides include animations and can be modified.
Use of the slides should mention their source.
Any posting of slides on a website must include a note about adapting the slides and copyright.
Authors of the slides are Jim Kurose and Keith Ross.

Chapter Goals

Understand principles behind network layer services.
Understand network layer service models.
Understand forwarding versus routing.
Understand how routers operate.
Understand routing (path selection).
Understand broadcast, multicast, and instantiation, implementation in the internet.

Chapter Outline

Introduction
Virtual circuit and datagram networks
What's inside a router
IP: Internet Protocol
- Datagram format
- IPv4 addressing
- ICMP
- IPv6
Routing algorithms
- Link state
- Distance vector
- Hierarchical routing
Routing in the internet
- RIP
- OSPF
- BGP
Broadcast and multicast routing
Network layer protocols and functions

Network Layer

Transports segments from sending to receiving host
Encapsulates segments into datagrams
Delivers segments to the transport layer on receiving side
Network layer protocols are in every host and router.
Routers examine header fields in all IP datagrams passing through them

Two Key Network Layer Functions

Forwarding: Moves packets from a router's input to appropriate output port.
Routing: Determines route taken by packets from source to destination.
Routing algorithms are used to determine routes.

Interplay between Routing and Forwarding

The routing algorithm determines the end-to-end path through a network.
A forwarding table determines local forwarding at a router.
A header value in the packet's header is used to determine the output link.

Connection Setup

A third important function in network architectures
Establish virtual connections before datagrams flow.
Routers get involved in connection setup in some architectures like ATM, frame relay or X.25.

Network Service Model

Q: What service model for transporting datagrams from sender to receiver?
Individual datagrams: guaranteed delivery with less than 40 msec delay.
Flow of datagrams: in-order datagram delivery, minimum bandwidth guaranteed to a flow of datagrams, constraints on changes in inter packet spacing.

Network Layer Service Models: Table

Attributes: network architecture, service model, bandwidth, loss, order, timing, congestion feedback
Examples of architectures and service models are shown (including Internet, ATM, CBR, VBR, ABR, and UBR).

Virtual Circuits

The source-to-destination path behaves like a telephone circuit.
Performance is consistent and network resources are allocated in advance
Includes call setup & teardown ,VC identifier, and router state maintenance
Link-level and router resources can be allocated to virtual circuits.

Virtual Circuits Implementation

Consists of path from source to destination
Contains VC numbers for each link along path
Creates entries in forwarding tables in routers.
Packets carry VC number rather than destination address.
VC number can change on each link based on forwarding table.

Virtual Circuits: Signaling Protocols

Used to set up, maintain, and tear down VCs.
Used in ATM, frame relay and X.25 but are not used in the modern Internet.

Datagram Networks

No call setup; no state about end-to-end connections in routers.
No network-level concept of connection.
Packets are forwarded using destination host address
Forwarding tables only look at destination address rather than maintaining connections.

Datagram Forwarding Table

4 billion IP addresses but rather than each one, lists ranges (aggregate table entries) for simplicity.
Routers use destination address in arriving packets to look up next hop using a forwarding table.
Longest prefix matching is used in the tables, and it finds the longest match for destination address within the table.

Datagram or VC Networks: Why Choose One?

Internet (datagram): elastic service, many link types, different network characteristics, smart end systems (computers).
ATM (VC): evolved from telephony, strict timing and reliability requirements, need for guaranteed service, dumb end systems (telephones).

Router Architecture Overview

Routing protocols (e.g., RIP, OSPF, BGP) run within the router, to compute and update forwarding tables and push it to input ports.
Routing processor (control plane)
High-speed switching fabric
Forwarding data plane (hardware)

Input Port Functions

Physical layer: bit-level reception
Link layer (receive): receives frame and extracts the network-layer packet
Lookup: using forwarding table
Forwarding: Based on lookup
Queuing: to handle delay if packets come too quickly

Switching Fabrics

Transfer packets from input buffer to appropriate output buffer.
Switching rate: Transfer rate of packets from inputs to outputs
Three types of fabrics: memory, bus, crossbar
Memory/CPU based switching
Bus switching
Interconnection Network switching (faster than bus)

Switching via Memory

Packets are copied to system's memory.
Speed is limited by memory bandwidth.
2 bus crossings need to occur for each datagram

Switching via Bus

Datagrams from input port memory to output port memory via a shared bus.
Switching rate limited by bus bandwidth.
32 Gbps bus sufficient speed for access, enterprise routers

Switching via Interconnection Network

Allows overcoming bus limitations
Utilizes technologies like banyan networks, crossbars
It fragments datagram into smaller cells and switches cells through the fabric
Cisco 12,000 and above devices have this kind of architecture

Output Ports

Buffer packets from the switching fabric.
Requires buffering to handle differences between the rate at which data flows from the fabric and the output ports
Queuing: if arriving rate exceeds output line speed.
Scheduling: how datagrams from the queue are processed.

Input Port Queuing

Fabric slower; queueing at input queues could occur
Head-of-the-line blocking
Output Port Contention: only one packet is transferred at a time.

Buffering

The recent recommendation is that the buffering amount at the output ports is proportional to the link capacity and the RTT (round trip time).

ICMP

Internet Control Message Protocol
Used by hosts & routers to communicate network-level information.
ICMP messages (types and codes)
- Error reporting
- Echo request, reply

IPv6 Motivation

Initial motivation: 32-bit address space exhaustion.
Additional motivation: header format helps processing/forwarding, header changes accommodate QoS.

IPv6 Datagram Format

Fixed-length header (40 bytes)
No fragmentation allowed from the beginning.
Priority, flow label, next-header, hop limit, source, destination addresses in the header.

Other Changes from IPv4

Removed checksums
Options outside the header
ICMPv6 with Packet Too Big messages
Multicast group management functions

Transition from IPv4 to IPv6

Tunneling: IPv6 datagram carried as payload in IPv4 datagram among IPv4 routers.
Allows interoperability while IPv6 network deployment is still ongoing.

Subnets

Subnets are isolated network islands.
Interfaces with same subnet portion of the IP address can communicate directly without requiring a router.

Hierarchical Addressing: Route Aggregration

Efficient advertisement of routing information through ISP blocks and subnets with hierarchical addressing and aggregation
Route aggregation to advertisement from ISP to ISP and within Organizations reduces routing load and traffic.

Hierarchical Addressing: More Specific Routes

More specific routes for organizations, given by Internet service providers (ISPs).
Allows ISP-level route advertisements
Examples are shown in diagrams

IP Addressing: Last Word...

ICANN (Internet Corporation for Assigned Names and Numbers)
Allocates IP addresses, manages DNS, assigns domain names, and address resolution.

DHCP Overview

DHCP dynamically assigns the IP address to a client on a network
Protocols and messages involved in the process
- discover
- offer
- request
- ACK.
Useful for mobile users and when it dynamically assigns the IP address based on the network usage.

DHCP Client-Server Scenarios

arriving client needs the IP in a network
DHCP server gives an IP to the client.

DHCP: More than IP Addresses

DHCP can return addresses of first-hop router, DNS server, and network mask to client.

IP Addresses: How to Get One?

Hard-coded in a file by system administrator
DHCP(Dynamic Host Configuration Protocol)

NAT (Network Address Translation)

Motivation: Local networks use just one IP address for outside world visibility.
Implementation: Router needs NAT translation table to remember source IP & port to NAT IP & port mapping for outgoing datagrams and the opposite for incoming ones.

NAT Traversal Problem

Solutions: Static configuration to forward incoming connections through NAT.

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Description

Test your knowledge on the critical functions of the network layer, including forwarding, routing, and protocols. This quiz covers essential concepts that are foundational for understanding how data is transported across networks. Challenge your understanding of how routers manage IP datagrams and the different service models in the network layer.