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Systems Programming > L13: Networking > Flashcards

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
Q

Unix Shell Networking Tools:

mail

A

Send or recieve

Electronic Mail

26
Q

Unix Shell Networking Tools:

nslookup

A

Map a symbolic name

to a

numeric address

27
Q

Unix Shell Networking Tools:

ping

A

Time the packets traveling from

your host

to another

28
Q

Unix Shell Networking Tools:

traceroute

A

Display path

to another host

29
Q

Unix Shell Networking Tools:

telnet

A

Begin a Remote Login Session

30
Q

Unix Shell Networking Tools:

rcp

A

Copy files to another

Unix host

31
Q

Unix Shell Networking Tools:

whois

A

Display NIC information

about a host

32
Q

Unix Shell Networking Tools:

hostname

A

Display your

host’s name

33
Q

Unix Shell Networking Tools:

rlogin

A

Remotely login

to another Unix host

34
Q

Unix Shell Networking Tools:

rsh

A

Run a shell command

on another unix host

35
Q

Unix Shell Networking Tools:

rusers

A

Display User Accounts

on a host

36
Q

Unix Shell Networking Tools:

ftp

A

Begin a File Transfer Session

37
Q

Standard Services

and their Ports (8)

A
  • echo - 7
  • discard - 9
  • systat - 11
  • daytime - 13
  • ftp - 21
  • telnet - 23
  • smtp - 25
  • http - 80
38
Q

Ethernet :

Addressing

A
  • Addresses are 48 bytes long and fixed at factory
  • Physical address, stays with a computer where ever it moves
39
Q

Ethernet:

Packet Layout Sections

A
  • Preamble
  • Destination Address
  • Source Address
  • Frame Type
  • Frame Data
  • CRC
40
Q

Ethernet LAN Technology:

Connecting

A
  • 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
Q

Ethernet LAN Technology:

Messages

A
  • 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
Q

Problems of

Large Scale Networking

A
  • 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
Q

Ethernet:

History

A
  • Packet switched LAN technology
  • Invented at Xerox PARC in the 1970s
  • Now IEEE standard 802.3
44
Q

How Data is delivered

A
  • 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
Q

Basic Network

Connection Diagram

A
  • 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
Q

Diagram:

Client/Server

Programming Model

Work Flow

A

Systems Programming (17 decks)

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