L13: Networking Flashcards

1
Q

Symbolic Addressing:

Domain Name Services

A
  • A technique used to map domain addresses

Flow:

  1. Look in a local table for a match
    1. on Unix : /etc/hosts
  2. If None, as a DNS Server to find one of the domain’s servers
  3. Ask THAT server to completely resolve the symbolic address
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2
Q

Ethernet:

Hardware Specifications

A
  • Max cable length of 500 meters
  • Length can be extended with repeaters
  • Bandwidth: About 10 Mbps max transfer rate
    • Few fast or several slow slow computers
  • Several Cabling Schemes:
    • Thick Coaxial
    • Thin Coaxial
    • Twisted pair 10 Base-T
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3
Q

“Backbone” infrastructure

of the Internet

A
  • Connects Networks, Makes the Internet Global
  • Includes many Providers
  • Providers cooperate in moving the packets
  • Packets may go a round-about way, depending on traffic
  • Features:
    • High Speed Lines
    • routers
    • digital formats
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4
Q

Protocols defined

above IP (8)

A
  • TCP
  • FTP
  • TELNET
  • SMTP
  • SNMP
  • DHCP
  • NTP
  • UDP
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5
Q

Protocols:

TCP

A

Transmission Control Protocol

  • This is a reliable transport protocol service
  • Provides Robust Delivery
  • Most applications and many other protocols use TCP

Responsibilities:

  • Decomposition of messages into datagrams
  • Assume that all arrive and are in good condition
    • Use ack/nak and checksums
  • Assemble back into proper order
    • Uses sequence numbers
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6
Q

Protocols:

FTP

A

File Transfer Protocol

  • Transfers files using TCP
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7
Q

Protocols:

TELNET

A
  • Remote login protocol
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8
Q

Protocols:

SMTP

A

Simple Mail Transfer Protocol

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9
Q

Protocols:

SNMP

A

Simple Network Management Protocol

  • Helps find and query hosts
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10
Q

Protocols:

DHCP

A

Dynamic Host Configuration Protocol

  • Assign IP addresses at boot
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11
Q

Protocols:

NTP

A

Network Time Protocol

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12
Q

Protocols:

UDP

A

User Datagram Protocol

  • almost raw IP packets
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13
Q

Possible Issues

with

IP Delivery Service

A
  • Packets shouldn’t be longer than 1500 characters

Packets may:

  • be arbitrarily delayed
  • “die” and never arrive
  • arrive out of sequence
  • get data corrupted
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14
Q

Organizations that

Regulate Internet Protocols

A

Internet Engineering Task Force (IETF)

administers protocol proposals and analysis

Internet Architecture Board (IAB)

approves protocols and allocates addresses

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15
Q

Networking:

Major Topics (12)

A
  • Ethernet LAN technology
  • Bridges
  • Types of Networks:
    • Centralized
    • Decentralized
    • Distributed
  • Symbolic Addressing
  • Network Architecture/Backbone
  • MANs
  • How data is delivered
  • Protocols and Protocol Hierarchy
  • TCP
  • Unix Network Tools
  • Ports
  • Client-Server Model
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16
Q

Network Protocol Layers:

Layers of a single host

A

Upper to Lower:

  • Application
  • Networking Library
  • TCP
  • IP
  • Internet
  • Physical
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17
Q

Network Packet Layers

A

From Outer Layer to Inner Layer

Ethernet Packet

IP Datagram

TCP Packet

Library Wrapper

Data

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18
Q

Networking:

Ports

Overview

A
  • Servers use ports to announce Services
  • There are some Standard Ports
    • _​_These are created at boot
    • Stored in /etc/services
  • A client connects to a specific port
  • On the server, you can open a new port at any time
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19
Q

Symbolic Addressing:

Overview

A
  • Simplifies human use
  • Authority assigns a symbolic address domain

Format:

org.type

where org denotes the organization

type denotes the type of organization

Organization extends the address to name hosts within its network.

Ex: vancouver.wsu.edu

Symbolic Addresses are mapped to Domain Adresses by DNS

20
Q

Ethernet:

Bridges:

  • Operation
  • Attributes
A

Bridges connect separate ethernets

Operation:

  • Bridge has a list of ethernet addresses on each separate net
  • Packets are accepted from one side, forwarded to the other
  • Bridge is invisible(transparent) to the ethernet cards

Attributes:

  • An Adaptive Bridge learns each side’s addresses and forwards only as needed
  • Bridges do not propogate electrical noise(or repeaters), & follow collision rules, so can be used to extend an ethernet almost indefinitely
21
Q

Unix Shell Networking Tools:

netstat

A

Display which clients are connected

22
Q

Unix Shell Tools

for Networks (15)

A
  • whois
  • ping
  • traceroute
  • hostname
  • nslookup
  • netstat
  • ftp
  • telnet
  • mail
  • rcp
  • rlogin
  • rsh
  • rusers
  • rwho
  • rwall
23
Q

Unix Shell Networking Tools:

rwall

A

Send a message to

everyone on a host

24
Q

Unix Shell Networking Tools:

rwho

A

Display who is

logged in on a host

25
Unix Shell Networking Tools: mail
Send or recieve Electronic Mail
26
Unix Shell Networking Tools: nslookup
Map a symbolic name to a numeric address
27
Unix Shell Networking Tools: ping
Time the packets traveling from your host to another
28
Unix Shell Networking Tools: traceroute
Display path to another host
29
Unix Shell Networking Tools: telnet
Begin a Remote Login Session
30
Unix Shell Networking Tools: rcp
Copy files to another Unix host
31
Unix Shell Networking Tools: whois
Display NIC information about a host
32
Unix Shell Networking Tools: hostname
Display your host's name
33
Unix Shell Networking Tools: rlogin
Remotely login to another Unix host
34
Unix Shell Networking Tools: rsh
Run a shell command on another unix host
35
Unix Shell Networking Tools: rusers
Display User Accounts on a host
36
Unix Shell Networking Tools: ftp
Begin a File Transfer Session
37
Standard Services and their Ports (8)
* echo - 7 * discard - 9 * systat - 11 * daytime - 13 * ftp - 21 * telnet - 23 * smtp - 25 * http - 80
38
Ethernet : Addressing
* Addresses are 48 bytes long and fixed at factory * Physical address, stays with a computer where ever it moves
39
Ethernet: Packet Layout Sections
* Preamble * Destination Address * Source Address * Frame Type * Frame Data * CRC
40
Ethernet LAN Technology: Connecting
* Each computer has an Ethernet Card * The Card is special hardware with a unique address * In an ethernet LAN, every computer's card is connected to the same single piece of wire( a cable)
41
Ethernet LAN Technology: Messages
* Sender broadcasts a structured chunk of bytes( a packet) * Packet has address of sender/receiver and body of the message(payload) * Only the card with the receiver address accepts the message * If 2 senders attempt broadcast at same time (a collision), they both wait a random length of time and try again
42
Problems of Large Scale Networking
* How to connect large numbers of separate networks? * Networks may have incompatible physical addresses and data * May be multiple paths from destination to source * Machines assigned to various functions may change * No single entity can know where everything is * Response times cannot be guaranteed Solution: Internetworking agreements(protocols) that networks obey in communicating with each other. The most successful is TCP/IP
43
Ethernet: History
* Packet switched LAN technology * Invented at Xerox PARC in the 1970s * Now IEEE standard 802.3
44
How Data is delivered
* A Host breaks messages up into structured chunks called _packets_ * Packets have an address, read during delivery * Packets have data, not read during delivery * IPv4 packet Format is called "_Datagrams_", the basic unit of TCP/IP transfer * IP delivery service guarantees are very weak * Each packet is on it's own, so the service is called _connectionless_
45
Basic Network Connection Diagram
* **_Gateway_** * Maps addresses * Prevents access (firewall) * **_Internet Service Provider (ISP)_** * Provides local access * **_Point of Presence (PoP)_** * "on-ramp" to backbone * **_Backbone_** * High speed lines, "Interstate" * Digital formats * Routers
46
Diagram: Client/Server Programming Model Work Flow