Networking Concepts Quiz

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Questions and Answers

What addressing scheme is demonstrated through the transitions between organizations and ISPs?

Random addressing

Static addressing

Flat addressing

Hierarchical addressing (correct)

Which organization moved from Fly-By-Night-ISP to ISPs-R-Us?

Organization 1 (correct)

Organization 0

Organization 7

Organization 2

What more specific route does ISPs-R-Us advertise for Organization 1?

200.23.16.0/20

199.31.0.0/16

200.23.18.0/23 (correct)

200.23.20.0/23

What does Organization 2 use to request an address block from ISPs-R-Us?

199.31.0.0/16 Signup and view all the answers

Which range of addresses does the subnet 200.23.30.0/23 cover?

200.23.30.0 - 200.23.31.255 Signup and view all the answers

What is the primary function of the data plane within the network layer?

To move packets from a router's input link to the appropriate output link Signup and view all the answers

How do forwarding and routing differ in the context of network layer functions?

Forwarding selects the destination, while routing determines the best path Signup and view all the answers

Which component is part of the control plane in the context of traditional networking?

Routing algorithms implemented in routers Signup and view all the answers

What does the acronym SDN stand for in networking?

Software-Defined Networking Signup and view all the answers

What role does NAT play in network layer services?

It allows multiple devices to share a single IP address Signup and view all the answers

Which of the following best describes 'generalized forwarding' in networking?

The ability to process packets based on various fields, beyond just destination Signup and view all the answers

Which component of a router directly deals with the management of incoming and outgoing data packets?

Switching fabric Signup and view all the answers

What does CIDR stand for in network addressing?

Classless InterDomain Routing Signup and view all the answers

In the notation a.b.c.d/x, what does the 'x' represent?

The length of the subnet portion in bits Signup and view all the answers

Which of the following correctly represents a /24 subnet address?

223.1.2.0/24 Signup and view all the answers

How do hosts typically receive an IP address within a network?

Via a Dynamic Host Configuration Protocol (DHCP) Signup and view all the answers

Given the subnet 223.1.9/24, which of the following is the correct representation of its first usable address?

223.1.9.1 Signup and view all the answers

What is the primary advantage of using CIDR over traditional classful addressing?

It enables more efficient utilization of IP address space Signup and view all the answers

Which of the following best describes the subnet part of an IP address?

It differentiates between different networks Signup and view all the answers

What is a valid host address in the subnet 223.1.3.0/24?

223.1.3.254 Signup and view all the answers

What is the source IP address of the DHCP offer?

223.1.2.5 Signup and view all the answers

What does the 'yiaddr' field in the DHCP offer signify?

The IP address being offered to the client Signup and view all the answers

Which of the following statements is NOT correct about the DHCP request?

It always includes the server's IP address. Signup and view all the answers

What is the lifetime of the IP address offered in the DHCP offer?

3600 seconds Signup and view all the answers

What does the DHCP ACK message confirm?

The client's acceptance of the offered IP address Signup and view all the answers

Which of the following addresses is used for broadcasting DHCP messages?

255.255.255.255 Signup and view all the answers

In the DHCP request message, which field indicates the client wants to reuse a previously allocated address?

yiaddr Signup and view all the answers

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

To match requests with responses. Signup and view all the answers

How does a client convey its intention to use a previously allocated network address?

By indicating the IP address in the 'yiaddr' field of the request Signup and view all the answers

What DHCP message is sent in response to a valid request confirming an offer?

DHCP ACK Signup and view all the answers

What is the purpose of hierarchical addressing in network routing?

To allow more efficient advertisement of routing information Signup and view all the answers

How does an organization receive its subnet part of an IP address?

Through an allocation from its provider ISP's address space Signup and view all the answers

If an organization switches ISPs, what can be inferred about the routing advertisements?

The new ISP will advertise a more specific route to the organization. Signup and view all the answers

What is one likely benefit of route aggregation in hierarchical addressing?

It simplifies the routing process by combining multiple routes into one. Signup and view all the answers

Which of the following IP addresses represents a block allocated to Organization 1?

200.23.18.0/23 Signup and view all the answers

What indicates that Organization 1 is receiving a more specific route from its new ISP?

The address block may change from /20 to /23. Signup and view all the answers

What does an ISP do with its allocated address space?

It allocates portions of it to its customers. Signup and view all the answers

Which organization uses the address block 200.23.20.0/23?

Organization 2 Signup and view all the answers

What is the effect of ISPs advertising more specific routes?

It improves the precision of routing information. Signup and view all the answers

What is indicated by the IP notation /20?

It defines a larger address space than /23. Signup and view all the answers

Study Notes

Chapter 4: Network Layer: Data Plane

This chapter details the data plane of the network layer.
The provided slides are freely available for use, modification, and distribution under specific conditions
Users should reference the source (the textbook) and the copyright information if using the slides.

Network Layer: Our Goals

Understanding principles behind network layer services (focusing on the data plane).
Network layer service models.
Routing and forwarding.
Router architecture.
Internet architecture.
Implementation aspects of the Internet: including IP protocol, NAT (Network Address Translation), and middleboxes (e.g., firewalls).

Network Layer: "Data Plane" Roadmap

Network Layer Overview: encompassing data plane and control plane.
Router features: including input ports, switching, output ports, buffer management, and scheduling mechanisms.
IP (Internet Protocol) details: its datagram format, addressing schemes, and network address translation (NAT).
IPv6 protocols: addressing translation
Generalized Forwarding and SDN overview
Middleboxes (network devices performing additional functions)

Network-layer Services and Protocols

Network layer protocols function in all Internet devices.
Data segments are encapsulated into datagrams
Datagrams are passed to the link layer
Segment delivery is completed by the transport layer
Routers examine IP datagram header fields
Datagrams are transferred from input ports to output ports along the end-to-end path.

Two Key Network-Layer Functions

Forwarding: the process of moving packets from one router link to another based on look-up tables
Routing: the process that the router uses to plan the packet's trip from source to destination, involves routing algorithms

Network Layer: Data Plane, Control Plane

Data plane: local functions within a router determining how arriving datagrams are forwarded to router output port
Control plane: network-wide logic determining the path that a datagram takes from source to destination host. Approaches include traditional routing algorithms (in routers) and software-defined networking (SDN) implementations (remote servers)

Per-router Control Plane

Individual routing algorithm components in each router interact within the control plane.
Values from the arriving packet header are used to determine actions.

Software-Defined Networking (SDN) Control Plane

Remote controller (in a separate server) computes and installs the forwarding tables inside routers.

Network Service Model

Service models for network layers; for individual datagrams; example services.
Examples of services in flow of datagram: in-order datagram delivery, guaranteed minimum bandwidth to flow, restrictions on changes in inter-packet spacing

Network-layer Service Model QoS Guarantees

QoS guarantees depend on the network architecture and service model. The Internet's best-effort service model doesn't guarantee bandwidth, loss, or order of delivery.

Reflections on Best-Effort Service

Internet’s wide deployment is due to its simplicity.
Real-time applications’ performance is acceptable with sufficient bandwidth provisioning.
Replicated application-layer distributed services (e.g., data centers) contribute to the performance of real-time applications.
Congestion control mechanisms improve the efficiency of elastic services.

Router Architecture Overview

High-level view of a generic router architecture.
Routing processor: responsible for routing/management in millisecond time frame.
High-speed switching fabric: is the forwarding data plane (nanosecond time frame)
Input/output ports: used for packet transmission

Input Port Functions

Decentralized switching uses header field values to look up the appropriate output port using the forwarding table in input port memory.
The goal is to process input packets at line speed.

Destination-based forwarding, Longest Prefix Matching

Forwarding packets based on destination IP
Use longest prefix matching for look-up tables

Longest Prefix Matching

Use the longest matching address prefix when looking up entries in a routing table.
Ternary Content Addressable Memories (TCAMs) are used to enable efficient lookup, regardless of table size.
Cisco Catalyst routers use TCAMs for ~1 million routing entries.

Switching Fabrics

Transferring packets from input links to output links.
Switching rate = rate at which packets can be transferred from input to output ports
Measured as multiples of input/output line rate
Switching rate is desirable to be N multiplied by line rate in N inputs.

Switching via Memory

First-generation routers used traditional computers with switching under CPU control.
Packets were copied to system memory.
Speed was limited by memory bandwidth.

Switching via a Bus

Datagrams are transferred from input port memory to output port memory.
Switching speed is limited by bus bandwidth.
Example: 32 Gbps bus (Cisco 5600) is sufficient for access routers.

Switching via Interconnection Network

Crossbar, Clos Networks, and other interconnection networks were initially designed for multiprocessors.
They involve multiple stages of smaller switches, and exploit parallelism by fragmenting datagrams into cells, switching the cells, and reassembling datagrams at the exit.
Cisco CRS routers use multiple switching planes for high switching capacity, using a 3-stage interconnection network, with up to hundreds of Tb/s switching capacity.

Input Port Queuing

Queuing may occur if the switch fabric is slower than combined input ports. Delay may result from input buffer overflow.
Head-of-the-line (HOL) blocking occurs when a datagram at the front of queue blocks others from moving forward.

Output Port Queuing

Buffering required when datagrams arrive from fabric faster than link transmission rate
Drop policy is important in this context: which datagrams are dropped if no buffers are free.
Scheduling discipline decides queue order for transmission.

How Much Buffering?

RFC 3439 suggests that average buffering should equal the typical round-trip time (RTT) times the link capacity (C).
Increased buffering can increase delays in home routers.
Long RTTs lead to poor real-time application performance and sluggish TCP response.

Buffer Management

Drop: determining which packet to add when buffers are full.
Tail drop: drops arriving packets when buffers are full.
Priority: drop (or move) packets based on priority.
Marking: marking packets to indicate congestion (e.g., ECN and RED).

Packet Scheduling: FCFS

First-Come, First-Served. Packets are transmitted in the order they arrive at the output port. (FIFO- First-In, First-Out)
Priority: packets are classified into priority queues and transmitted from highest priority queue
Round Robin: server sequentially scans queues, servicing one packet from each class

Scheduling Policies: Weighted Fair Queuing (WFQ)

Generalized Round Robin : each class, i , has weight, w, gets a weighted amount of service during each cycle (∑WI).
Minimum bandwidth guarantee per class.

Sidebar: Network Neutrality

Technical: How an ISP should share/allocate its resources (Packet Scheduling and buffer management).
Social, Economic: Protecting free speech, encouraging innovation, and competition.
Enforced legal rules and policies.
Different countries have different "takes" on network neutrality.

Sidebar: Network Neutrality (FCC Order 2015)

No Blocking
No Throttling
No Paid Prioritization

ISP: Telecommunications or Information Service?

Title II: imposes "common carrier duties" on telecommunications services.
Title I: applies to information services

IP Datagram Format

Version number
Header length
Type of service
IP identifier, flags, fragment offset
Time to live, upper layer protocol, checksum
Source/destination IP addresses
Options
Payload (variable length)

IP Addressing: Introduction

IP address: 32-bit identifier.
Interface: connection between host (or router), and physical link.

Subnets

Subnet: devices in the same subnet have the common high-order bits in their IP addresses.
Host part: the remaining low-order bits of the IP address

Subnets (Recipe, Addressing Structure, CIDR)

Recipe: detach each interface from its host, and router, creating "islands" of isolated networks. Every island is a subnet.
Structure: Subnet + host.
CIDR (Classless Inter-Domain Routing): subnet portion of an address of arbitrary length, allowing more flexible use of address space

IP Addresses: How to Get One?

Hard-coded (manual input by sysadmin)
DHCP (Dynamic Host Configuration Protocol): from a server during system boot and network access

DHCP: Dynamic Host Configuration Protocol

Host dynamically obtains IP address from a network server when it joins.
Renewing leases, address reuse, mobile user support (joining/leaving network).
DHCP Discover / Offer / Request / ACK messages exchanged.

DHCP: More Than IP Addresses

Additional information DHCP may return:
First-hop router's address
DNS sever's address
Network mask

DHCP: Example

DHCP is used dynamically obtain IP address for devices connecting to the network (laptop).
Messages are encapsulated in UDP, IP, and Ethernet. -DHCP server sends address: DHCP ack

IP Addresses: How to Get ISP Block of IP Address Space?

ICANN (Internet Corporation for Assigned Names and Numbers) allocates blocks of addresses to ISPs via regional registries
ISPs may distribute further across their network using subnet blocks, creating more addresses for individual organizations and devices.

Hierarchical Addressing: (Route Aggregation)

Hierarchical addressing simplifies routing advertisement.

Hierarchical Addressing: (More Specific Routes)

When an organization moves ISPs, more specific route aggregation is used.

IP Addressing: Last Words

ICANN allocates IP blocks through regional registries (RRs) to ISPs. Management includes delegation of TLDs (.edu, .com).
NAT and address space exhaustion are handled with NAT, which can be controversial
IPv6 is used for address space extensibility.

IPv6 Motivation

Motivation: 32-bit IPv4 space is fully allocated.
40-byte header.
Enables different network-layer treatment of "flows."

IPv6 Datagram Format

Priority/Flow Label
Fixed length 40 byte header
Source/destination addresses
Payload

Transition From IPv4 to IPv6

Gradual transition due to incompatibility between IPv4 and IPv6 routers
Tunneling (carrying IPv6 datagrams inside IPv4 datagrams) enables interoperability

Tunneling and Encapsulation

Tunneling is an important mechanism for transitioning from IPv4 to IPv6.

IPv6 Adoption

Google and NIST are using IPv6 with increasing numbers of clients and domains respectively.
25 years and counting! Significant application-level advancements have occurred in this time frame

NAT: Network Address Translation

Local network devices share a single network address (as seen by the outside world)
The NAT router translates source and destination addresses.

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Description

Test your knowledge on various networking concepts, including addressing schemes, SDN, NAT, and the differences between forwarding and routing. This quiz covers essential topics related to the network layer and control plane functions. Perfect for those studying computer networking and information systems.