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0-CWO > 4 - Network Fundamentals > Flashcards

4 - Network Fundamentals Flashcards

1
Q

Benefits of layered network model approach

A

Easier troubleshooting

Standardizes networking architecture

Allows vendor interoperability

Each layer only communicates with peer layer

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2
Q

TCP/IP

A

Network model developed by DARPA and university volunteers

Became standard by late 90s

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3
Q

RFC

A

Request for Comment

Used to define standardized protocols

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4
Q

Network Model Layers
– OSI
– TCP/IP (old and new)

A
  • OSI
    1. Physical
    2. Data Link
    3. Network
    4. Transport
    5. Session
    6. Presentation
    7. Application
  • TCP/IP (Old)
    1. Link
    2. Internet
    3. Transport
    4. Application
  • TCP/IP (New)
    1. Physical
    2. Data Link
    3. Network
    4. Transport
    5. Application
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5
Q

PDU

A

Generic term for unit of info transmitted within network model

Physical - Bits
Data Link - Frame
Network - Packet
Transport - Segment (TCP), Datagram (UDP)
Application - Data

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6
Q

Application Layer (TCP/IP)
- Purpose/Functions
- Example protocols

A
  • Provide services to app software
  • Defines how programs interface w/ transport layer
  • Functions:
    – ID’ing communication partners
    – Determining resource availability
    – Synchronizing communication

Examples: HTTP, DNS, DHCP, HTTPS, FTP, TFTP, Telnet, SSH, NTP, SNMP

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7
Q

DHCP
- Port
- Description
- Layer
- Min info obtained

A
  • UDP Port 67 (client to server, broadcast) and 68 (server to client, unicast)
  • Dynamically assign IP address, lease length, subnet mask, and default gateway (minimum) and DNS IP (optional)
  • Uses “DORA” process
  • Application Layer
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8
Q

DORA

A
  • Discover, Offer, Request, Acknowledgement
  1. DHCP Client broadcasts to find DHCP server
  2. Server offers IP address/parameters
  3. Client accepts
  4. Server acknowledges acceptance and delivers lease info
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9
Q

DNS
– port
– layer

A

TCP/UDP Port 53

Application Layer

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10
Q

HTTP

A

TCP 80, 8008, 8080

Identified using URIs or URLs, used since 1990

Application Layer

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11
Q

HTTPS
– Port
– Info
– Layer

A

TCP 443

If NTP is not synchronized, cert signing can fail

Self-signed certificates provide confidentiality but do not confirm identity

Application Layer

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12
Q

FTP
– port
– layer

A

TCP 20 (Data) and 21 (Control)

Application Layer

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13
Q

TFTP
– Port
– Description
– Layer

A
  • UDP 69
  • Very basic FTP functionality
    – Requires small amount of memory
    – Can only read and write files from/to a remote server
    – Cannot list directories
    – No user authentication
    – Typically used for storage/retrieval of Cisco switch config files
  • Application Layer
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14
Q

Telnet
– port
– layer

A

TCP 23

Sends username/PW in plaintext

Application Layer

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15
Q

SSH
– Port
– Layer

A

TCP 22

Application Layer

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16
Q

NTP
– Port
– Description
– Layer

A

UDP 123

Synchronize time down to a millisecond or fraction of a millisecond

Can use different methods such as radio and satellite

Application Layer

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17
Q

Transport Layer (TCP/IP)
– Description/functions
– Example protocols

A

Communication session management

Defines level of service and status of connection when transporting data

Examples: TCP and UDP

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18
Q

TCP (Protocol)

A
  • Two functions:
    – Flow control provided by sliding windows
    – Reliability provided by sequence numbers and acknowledgements
  • Breaks messages into segments
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19
Q

TCP Segment Header
- Fields

A

Fields:
source port
destination port
sequence/acknowledgement numbers
control bits (SYN, ACK, FIN, etc.)
window size

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20
Q

TCP Window Size

A

Controls communication flow
sets # of messages transmitted before waiting for ack (ack # matches the seq number of the next segment to be sent)

Ex: Window size 1 - each segment must be acknowledged before another is sent

Can be changed to maximize bandwidth efficiency

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21
Q

UDP Header

A

64 bits long

Only includes Source port, Destination port, Length, and checksum

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22
Q

Socket
– Purpose
– 3 Parts

A

Used to track different concurrent network sessions

Includes IP address, TCP/UDP, and port number

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23
Q

Port number ranges

A
  • Well-known: 0-1023
  • User/Registered: 1024-49151
    – Users connect to registered ports using ephemeral source ports
  • Dynamic/ephemeral: 49152-65535 (1025-5000 if older than win XP)
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24
Q

TCP/IP Layer Interaction

A

Adjacent layers work together on the same system

Same layers communicate with the same layer on a different system

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25
Q

Network Layer (TCP/IP)

A

Primary protocol is IP

Packages data into IP datagrams

Routes IP datagrams

Protocol Ex: IPv4/6, ARP, ICMP (ping)

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26
Q

Internet Protocol (IP)

A

Defines how data is sent from one computer to another on the internet

Messages divided into “packets”

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27
Q

IPv4 Packet Structure

A

Divides data segments (from Transport Layer) into packets

Encapsulated data called IP Payload

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28
Q

IPv4 Header
– Size
– Fields

A

Max size 60 bytes, min 20 bytes

Includes info such as as IP version, Internet header length (IHL), Differentiated Services Code Point (DSCP)(type of service), Total Length of entire IP packet, Identification number, Flags, Fragment Offset, TTL, Protocol, Header Checksum, Source Address, Destination Address, and Options

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29
Q

IPv6 Packet Structure
– Two parts

A

Two main parts: Header/header extensions and Payload

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30
Q

IPv6 Header
– 8 items

A

Fixed 40 byte length

Contains:
- Version (4 bit)
- Traffic class (8 bits describing packet’s priority)
- Flow Label (20-bits for QoS Management)
- Payload Length (16-bit)
- Next Header (describes next extension header or where payload begins)
- Hop Limit (8 bits, similar to TTL)
- Source Address (128 bits)
- Destination Address (128 Bits)

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31
Q

IPv6 Packet Contents

A

Two Parts:
Extension Header – move variable length fields from IPv4 headers into the packet, such as authentication extension header and encapsulating security payload extension header
Upper Layer Protocol Data Unit (Payload) – comes after final extension header

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32
Q

ARP

A

Map IP address to MAC address

Allows communication on Ethernet LAN

Layer 2 protocol

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33
Q

ICMP

A

Provides feedback about problems in the network

Usually formed from a normal IP packet that has generated an ICMP response

Uses the following defined messages:
- Destination Unreachable
- Time Exceeded
- Parameter Problem
- Subnet Mask Request
- Redirect
- Echo
- Echo Reply
- Timestamp
- Timestamp Reply
- Information Request
- Information Reply
- Address Request
- Address Reply

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34
Q

Data Link Layer (TCP/IP)

A

Handles MAC addressing

Detects errors that may occur in physical layer
Frame Check Sequence - receiver checks for frame transmission errors and discards frame if one occurs

Primary protocols: Ethernet (IEEE 802.3) and PPP, STP

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35
Q

MAC Address

A
  • hardware’s physical address, tied to NIC
  • Layer 2 address
  • Can’t be changed but may be spoofed
  • 48 bits in length
    – First 6 hex digits (24 bits) = organizational unique identifier (OUI)
    – Last 6 (24 bits) are interface serial number
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36
Q

Ethernet Frame Structure

A

IEEE 802.3 standard

Includes:
- Preamble – signals start of frame and enables sync
- Start Frame Delimiter (SFD) – Signifies that destination MAC starts next byte
- Destination MAC
- Source MAC
- Type – Defines protocol inside the frame (IPv4/6, etc.)
- Data and Pad – Payload Data (46 bytes)
- Frame Check Sequence (FCS) – 32-bit cyclic redundancy check (CRC) for detecting corrupted data

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37
Q

Spanning Tree Protocol (STP)

A

Prevents frame loops within a switched network

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38
Q

Physical Layer (TCP/IP)

A

Encodes a signal onto medium for transmission

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39
Q

IEEE 802.3 media types

A

Coax
Twisted Pair (UTP/STP)
Fiber Optic

40
Q

Coax

A

Consists of center core, surrounded by dielectric insulator, metallic shield, and finally plastic jacket

Still used with cable modems

41
Q

Twisted pair cabling

A

Unshielded:
Four color-coded pairs
Cat 3, 5, 5e, and 6
Common connectors: RJ-11 and RJ-45 (standard)
Can use straight-through (unlike) or crossover cables (like)

Shielded:
Additional metal shielding around each pair or collection of pairs to reduce EMI
Primarily used in data networks

42
Q

Fiber Optic Cables

A

Two modes:
Single Mode (SMF)
Multi Mode (MMF)

43
Q

Single Mode Fiber (SMF)

A

Transmits using laser and glass core

Higher bandwidth and greater cable distance

44
Q

Multi-Mode Fiber (MMF)

A

Transmits using LED
Larger core, typically plastic

Signal bounces off reflective surfaces and Light travels different distances depending on entry angle (modal dispersion)

Cheaper than SMF

45
Q

Encapsulation/De-encapsulation

A

Adding headers/trailers around data, and removing headers to process data inside

46
Q

IEEE

A

Institute of Electrical and Electronics Engineers

Non-Profit

Several categories:
802.1X - Authentication
802.3 - Ethernet
802.11 - Wireless
802.15 - WPAN
802.15.1 - Bluetooth
802.16 - WMAN

47
Q

802.1x

A

Authentication

Port-based Network Access Control
Authentication mechanism for connecting to LAN/WLAN
Provides protection for other types of authentication such as remote access and VPN

48
Q

802.3

A

Ethernet

Xerox, 1983, 802.3 CSMA/CD

Standards for physically connected networks

1980s - Ethernet (10Mbps) - Copper
1990s - Fast Ethernet (100Mbps) and 1000BASE-T (1 Gbps) - Copper
2018 - 200GBASE-X (200Gbps) - Fiber

49
Q

CSMA/CD

A

Rules governing communication over Ethernet

  • Carrier - Network signal
  • Sense - Ability to detect
  • Multiple Access - Equal access for all devices
  • Collision - What happens when devices send at once
  • Detection - How computers handle collisions

Devices wait until line is free, but when collision does occur, each device waits a random time then retransmits

50
Q

10BASE2/5

A

“Thinnet”/”Thicknet”
Coax
One problem affects whole LAN
Uses physical bus (vampire taps) or logical bus (Hub)

51
Q

Hub (topology)

A

One device talks at a time
1 collision/broadcast domain

52
Q

10BASE-T

A

Twisted Pair Ethernet
UTP cabling
One problem does NOT affect whole LAN
star topology w/ bridge or switch

53
Q

Bridge

A

2-4 interfaces
separate collision domain for each interface
adds bandwidth (half duplex)
Uses SOFTWARE to forward/filter frames (slower)

54
Q

Switch

A
  • 24-48 interfaces
  • Separate collision domain for each interface
  • Adds bandwidth (full duplex)
  • Uses HARDWARE to forward/filter frames (faster)
  • Learns MAC addresses:
    – Listens to frames
    – Source MAC and interface added to CAM table
  • Primary function - forward/filter frames based on CAM tables
  • Inactive MACs removed (300 secs default) to make room for new ones
  • Uses STP and places ports in forward or block state to prevent layer 2 (frame) loops
55
Q

Switching logic

A

Unicast - ID single LAN interface card

Broadcast - all devices (FFFF.FFFF.FFFF) (switch does not learn addresses)

Multicast - dynamic subset of devices (switch does not learn addresses)

56
Q

Switch forward/filter decision

A

Switch receives frame

If MAC destination is in table, forward to that interface. Otherwise, flood to all interfaces (ARP)

57
Q

Collision Domain

A

Domain in which frame sent by one NIC could result in a collision with a frame from another NIC

One physical segment (shared medium)

Layer 2 devices separate collision domains by each interface

Layer 1 devices like hubs do not separate collision domains regardless of interfaces used

58
Q

Broadcast Domain

A

Domain in which broadcast frame sent by one NIC is received by all other NICs

Routers ignore broadcasts

59
Q

LAN design considerations

A

Total devices per collision domain

Broadcasts

Segment large LAN w/ routers to reduce bandwidth consumption from broadcasts

Break up collision domains with layer 2 devices.
Break up broadcast domains with layer 3 devices.

60
Q

802.11

A

Wireless

MAC and physical specifications for implementing Wireless LAN (WLAN)

61
Q

Wireless Specifications

A

802.11a - 11 Mbps
802.11b - 54 Mbps
802.11g - 54 Mbps
802.11n - 450 Mbps
802.11ac - 1 Gbps

62
Q

IPv4 Classes

A

Class A - Internet hosts - 0-127
Class B - Internet hosts - 128-191
Class C - Internet hosts - 192-223
Class D - Internet multicasts - 224-239
Class E - Used experimentally - 240-255

63
Q

Private IPv4 Ranges

A

Non-routable on public networks/internet

10.0.0/8

172.16-31.0.0/12

192.168.0.0/16

64
Q

Special IPv4 addresses

A

127.0.0.1/8 - Loopback
THIS computer
Tests TCP/IP software but NOT the NIC

169.254.0.00/16 - Auto assigned private IP address
Allows LAN communication when no DHCP server can be reached/exists

65
Q

IPv4 Ethernet Addressing
– “cast” options

A

Unicast - One sends to one

Multicast - One sends to many - Network copies data and delivers to each destination

Broadcast - One sends to all destinations on network - network copies data and sends to all destinations on network

66
Q

IPv6 Benefits

A

More IP addresses
Better security
Optional NAT
Simpler header format
More efficient routing
Easier admin

67
Q

Special IPv6 addresses

A

::1 - loopback
::/128 - unspecified
FE80::/10 - link local
FC00::/8 or FD00::/8 - Unique local
2000::/3 - global unicast
FF00::/8 - multicast

68
Q

Types of IPv6 addresses

A

Global Unicast - globally routable

Unique Local - Private IP, routable in private network

Link Local - Routable within broadcast domain

69
Q

IPv6 Addressing
–“Cast” options

A
  • Unicast - Single Interface, similar to IPv4
  • Multicast - Replaces IPv4 Broadcast - Packets delivered to every interface in a group
  • Anycast - Typically used to locate nearest specific server, such as DNS/DHCP - Single address assigned to multiple nodes
70
Q

Hub (network device)

A

Connects computers in a star topology

Transmits to every attached line in half-duplex (one signal can be sent OR received at a time)

Operates at Layer 1, not a smart device

71
Q

Repeater

A

Used to regenerate/boost signals farther than max range (100m for twisted pair, for example)

Operate at Layer 1

72
Q

Modem

A

Modulator-Demodulator

Converts carrier signal between analog and digital mode

Operates at Layer 1

73
Q

Media Converter
– Description
– Layer

A

Allows connection/interoperability between dissimilar media types (such as UTP and fiber)

Operates at Layer 1

74
Q

NIC

A

Implements electronics allowing physical and data link layer connections to a network

Often built into motherboard, but can be standalone card

75
Q

Bridge
– Description
– Layer

A

Works at Layer 2 OSI

Reduces traffic on LAN by dividing it into two collision domains

76
Q

Basic Switch

A

Operates mostly at Layer 2 OSI

Each port is a collision domain

77
Q

WAP (Wireless Access Point)

A

Operates at Layer 2 OSI

Allows wireless devices to connect to wired network using Wi-Fi

Access Point usually connects to router but can be integrated into router itself

78
Q

Basic Router

A

Operates at Layer 3 OSI

Connects two or more networks by forwarding packets between them

Uses routing table to select best path

Breaks up broadcast domains

79
Q

Basic Firewall

A

Operates at Layer 3 and 4 OSI

Monitor and control in and out network traffic

Uses set of predefined rules to create barrier between trusted/untrusted connections/devices

80
Q

OSI Layer 1
– Name
– PDU
– Devices
– TCP/IP Equivalent

A

Physical

PDU: Bit

Devices: Hub, Modem, Repeater, Cables, Media Converters, and NIC

TCP/IP equivalent: Link (old) or Physical (new)

81
Q

OSI Layer 2
– name
– PDU
– Devices
– TCP/IP equivalent
– Header/trailer fields

A

Data Link

PDU: Frame

Devices: Switch, Bridge, WAP, NIC

TCP/IP Equivalent: Link (old) or Data Link (new)

Header/Trailer Fields: Preamble, SFD, Dest/source MAC, Type, FCS

82
Q

OSI Layer 3
– name
– PDU
– Devices
– Protocols
– TCP/IP equivalent
– Header/trailer fields

A

Network

PDU: Packet, IP Datagram

Devices: Router, Multilayer Switch, Firewall

Protocols: IP, ARP, ICMP, IPv4/6

TCP/IP Equivalent: Internet (Old), Network (New)

Header/Trailer Fields: IHL, TTL, Source/Dest IP

83
Q

OSI Layer 4
- Layer name
- PDU
- Devices
- Protocols
- TCP/IP Equivalent
- Header/trailer fields

A

Transport

PDU: Segment (TCP), Datagram (UDP)

Devices: Firewall

Protocols: TCP, UDP

TCP/IP Equivalent: Transport (Both)

Header/Trailer Fields: Source/Dest port, Window size, Control bits (Syn/Ack, etc.)

84
Q

OSI Layer 5, 6, and 7
– Names
– PDU
– Devices
– Protocols
– TCP/IP Equivalent

A

Session, Presentation, Application

PDU: Data

Devices: Clients, Servers, Application Layer security appliances

Protocols: HTTP/S, POP3, SMTP, DNS, FTP, Telnet, SSH (all for application layer)

TCP/IP Equivalent: Application (Both)

85
Q

Bus Topology

A

Every station shares the media and can see all traffic

One failure affects all nodes

Think straight line

86
Q

Ring Topology

A

Can be bidirectional or unidirectional

If unidirectional, second link is necessary for redundancy

Each host connected to two other hosts, in a ring shape

87
Q

Star Topology

A

One central device connects to several others, typically with a hub or switch

Switch = physical star & logical star
Hub = physical star & logical bus

88
Q

Physical star

A

all nodes physically connected to central device

89
Q

Logical star

A

All nodes in separate collision domains

90
Q

Logical bus

A

All nodes in same collision domain

91
Q

Mesh Topology

A

Each device is connected to every other device in network

Extremely reliable and provides redundancy

High admin overhead and requires exponential cabling

92
Q

Hybrid Topology

A

Combination of two or more network topologies

Flexible, reliable, increased fault tolerance, easy to add new nodes, easy to diagnose

Difficult to manage and expensive

93
Q

Circuit switched networks

A

Dedicated path between nodes, such as in telephone network

Data sent as stream of bits through sequence of predetermined links in network

Delivery guaranteed

Each data unit knows entire path address provided by source

Resource reservation due to fixed path

94
Q

Packet Switched Networks

A

Routers determine addressing

Processes digital signals and routes through multiple pathways

Delivery not guaranteed

Each data unit knows only the final destination, intermediate path is determined by routers

No resource reservation due to shared bandwidth

95
Q

Virtual Circuit

A

Process of providing connection-oriented service between hosts over packet-switched network (e.g. TCP)

Essentially, emulates circuit-switched process over packet-switched network

Guaranteed Delivery

96
Q

DSCP

A

mechanism for classifying/prioritizing network traffic on IP networks. part of IPv4 Header

0-CWO (10 decks)

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