networking and/with the computerseas3.elte.hu/itcourse-2009/networking.pdf · 2 computer networking...

Networking and/with the computer

László Kálmán1 Csaba Oravecz1 Péter Szigetvári1,2

1Research Institute for LinguisticsHungarian Academy of Sciences

2Department of English LinguisticsEötvös Loránd University

Lecture 6–7. / 14, 21 Oct, 2009

Kálmán, Oravecz, Szigetvári Networking

Outline1 Introduction

Sample exam question2 Computer networking

Sharing informationNetwork types and topologies

3 Back to the hardwareNetwork devices

4 Network addressingIP addressesDomain namesLAN configuration

5 The Internet and the World Wide WebThe Web

6 Connecting to remote machinesRemote loginFile transferMailingMailing list, newsgroups, forumsOther social netfacilitiesNetiquette

7 History


Introduction

abstract

this lecture tells you about


Introduction

abstract


• setting up and connecting to a Local Area Network


Introduction

abstract



• the World Wide Web


Introduction

abstract




• using computer networks for common tasks such asconnecting to remote machines, transferring files, sendingmail


Introduction

abstract





The meaning of symbols used


Introduction

abstract






✌


Introduction

abstract






✌ → live demo on stage!


Introduction

abstract







✔


Introduction

abstract







✔ → correct/advantage/encouraged


Introduction

abstract








✘


Introduction

abstract








✘ → incorrect/disadvantage/discouraged


Introduction Sample exam question








7 History



Sample exam question

How much net work could a network work, if a networkcould net work?



Typical computer environments of students




Figure: Home “lab”




Figure: Home “lab” Figure: University lab


Computer networking Sharing information








7 History



Isolation is secure but inconvenient

Information is there to be shared• efficiently

• quickly

• in large amounts

• cost effectively.



Isolation is secure but inconvenient

Information is there to be shared• efficiently

• quickly

• in large amounts

• cost effectively.

Most of data on computers is information. To share thiscomputers must communicate with each other. How?



Network, my choice is.

Link computer systems together, we must.




Computer network

Two or more computers that are linked in order to shareresources (eg. printers), exchange files, allow electroniccommunications.




Computer network

Two or more computers that are linked in order to shareresources (eg. printers), exchange files, allow electroniccommunications.

Link types

• cables

• telephone lines

• radio waves

• satellites

• infrared light beams


Computer networking Network types and topologies








7 History



Network topology



Network topology

The physical topology of a network refers to . . .

the configuration of cables, computers, and other peripherals.



Network topology

The physical topology of a network refers to . . .

the configuration of cables, computers, and other peripherals.

Figure: Star topology

Star topology

• easy to install and wire• no disruptions to the network

when connecting or removingdevices

• easy to detect faults and toremove parts



Network types (some, not all)




Figure: LAN

Local Area Network• confined to a limited geographic

area (building, college campus)• high data traffic• uses Ethernet technology• communication standard

(protocol): TCP/IP




Figure: LAN

Local Area Network• confined to a limited geographic

area (building, college campus)• high data traffic• uses Ethernet technology• communication standard

(protocol): TCP/IP

Wireless LAN

Using high frequency radio waves ittransmits data over the air minimizingthe need for wired connections. WLANsgive users mobility: they allowconnection to a local area networkwithout having to be physicallyconnected by a cable.



Network types



Network types

Figure: WAN



Network types

Figure: WAN

Wide Area Network• covers a broad

geographical area

• combines multiple LANs

• largest: ?



Network types

Figure: WAN


geographical area


• largest: Internet



Network types

Figure: WAN


geographical area


• largest: Internet

• may be built for oneparticular organization tobe private or by Internetservice providers (ISP) toprovide connections froman organization’s LAN tothe Internet



Typical students’ wishes




At home

I want to set up a small WLAN for my home. (I have a desktopPC, two notebooks, a network printer and a fridge.) How can Ido it and what devices will I need?




At home

I want to set up a small WLAN for my home. (I have a desktopPC, two notebooks, a network printer and a fridge.) How can Ido it and what devices will I need?

At the university

I’m sitting in the university lab in front of a thin display. Theremust be some program running since there is a small window inthe middle like this . . .



Login windows

like this . . .



Login windows

like this . . . or like this . . .



Setting up a home LAN

?cable/ADSL modem

router(+switch)+Access

Point (AP)

��

Figure: This will hopefully be a working home LAN


Back to the hardware Network devices








7 History



Network interfaces: ethernet card

To connect to a network computers must have some network interface. Fora desktop PC it is commonly an ethernet card, with a designated sockettype and cable.



Network interfaces: ethernet card

To connect to a network computers must have some network interface. Fora desktop PC it is commonly an ethernet card, with a designated sockettype and cable.

Figure: Ethernet network cardFigure: Network cable



Network interfaces: wireless

Wireless network interface controller (WNIC)

A network card which connects to a radio-based computernetwork.

No image :( Why?






No image :( Why?

Most common in notebook computers (and Macworkstations) and there it is integrated on the motherboard.






No image :( Why?

Most common in notebook computers (and Macworkstations) and there it is integrated on the motherboard.Today it’s impossible to buy a laptop which does not have it!






No image :( Why?

Most common in notebook computers (and Macworkstations) and there it is integrated on the motherboard.Today it’s impossible to buy a laptop which does not have it!

For a desktop PC it could just be yet another PCI card.



MAC address

Media Access Control address

A unique identifier attached to most forms of networkingequipment including the interfaces we’ve talked about. Printedin hexadecimal format:



MAC address



01-23-45-fc-89-ab



MAC address



01-23-45-fc-89-ab

00:08:74:4C:7F:1D



MAC address



01-23-45-fc-89-ab

00:08:74:4C:7F:1D

Q: How many possible addresses are there?



MAC address



01-23-45-fc-89-ab

00:08:74:4C:7F:1D

1612= 248

= 281, 474, 976, 710, 656



MAC address



01-23-45-fc-89-ab

00:08:74:4C:7F:1D

1612= 248

= 281, 474, 976, 710, 656

• Not expected to be saturated before 2100.



MAC address



01-23-45-fc-89-ab

00:08:74:4C:7F:1D

1612= 248

= 281, 474, 976, 710, 656

• Not expected to be saturated before 2100.

We will see that you might well need this information. . .



Home network checklist

?cable/ADSL modem


Point (AP)

��

Figure: So far, so good. . .




?cable/ADSL modem


Point (AP)

��

Figure: So far, so good but some devices are still missing. . .



Modems providing broadband internet access




Cable modemprovides network access by using the cable televisioninfrastructure.





ADSL (Asymmetric Digital Subscriber Line) modem

provides digital data transmission over the wires of a localtelephone network.





ADSL (Asymmetric Digital Subscriber Line) modem

provides digital data transmission over the wires of a localtelephone network.

Internet Service Provider (ISP)

The organization that sells access to the Internet and relatedservices.



Connection established. . .




We

have already contacted our ISP and the service is up and running now athome.




We


Still to be done

The ISP provides you with a single cable line through the modem devicea

to which we can connect with one computer having an ethernet card.That means you are just a node in the ISP’s LAN/WAN! But. . .

aCable modems remain the property of the ISP.




We


Still to be done



• We take a fancy to wireless networking.





We


Still to be done



• We take a fancy to wireless networking.• We need to have all our computers with access to the internet.





We


Still to be done



• We take a fancy to wireless networking.• We need to have all our computers with access to the internet.• All of our home devices should be able to communicate with each

other (printer and fridge incl.).





We


Still to be done



• We take a fancy to wireless networking.• We need to have all our computers with access to the internet.• All of our home devices should be able to communicate with each

other (printer and fridge incl.).• After all, that’s the whole point of a home LAN!




Useful info

The speed of data transfer through the network is measured inbit/s (bps). 128 kbit/s (Kbps) today is considered low even forhome networking. ISPs offer services up to several Mbps butthis has its price. To download high quality movies you willneed this several Mbps, nevertheless. For average homeinternet use, however, a basic 1 Mbps download bandwidthservice will suffice.



Connection to be established. . .

We have two LANs here to deal with:




We have two LANs here to deal with:• the ISP’s LAN/WAN





• our home LAN





• our home LAN

Only the former is connected to the Internet, so we have tomake a link between our home LAN and the ISP’s LAN/WAN(“represented” by the modem). For this we need a specialdevice . . .




?cable/ADSL modem


Point (AP)

��

Figure: So far, so good




?cable/ADSL modem


Point (AP)

��

Figure: So far, so good and there are no devices missing!?



The network fridge, it is.

The Fridge with network interface, in our home, we haveyet not.



(Wireless) router

Figure: The back of a wirelessrouter

Multiple devices in one



(Wireless) router



• switch for the LAN(connecting devices within)



(Wireless) router




• access point for thewireless network(connecting it to the wiredLAN)



(Wireless) router




• access point for thewireless network(connecting it to the wiredLAN)

• router: junction betweentwo or more networks totransfer data packetsamong them


Network addressing IP addresses








7 History



Sending data

Hardwarewise everything is set up . . .



Sending data


• use the network: send and recieve data



Sending data



• to whom and where?



Sending data




• MAC address ≈ personal identification number; tells youwho you are but not where you are



Sending data





• postal address



Sending data





• postal address → IP Address



Sending data





• postal address → IP Address

Data fragments

Data through the network is split up into packets, each labeledwith the complete destination address.



Network addresses

Figure: Network addresses are like house numbers and street names



IP addresses



IP addresses

• When connected, all network devices must have a unique IP.



IP addresses

• When connected, all network devices must have a unique IP.• IP address assignment is supervised by the Internet Assigned

Numbers Authority (IANA).



IP addresses


Numbers Authority (IANA).• IANA delegates local registrations of IP addresses to Regional

Internet Registries (RIRs).



IP addresses




Address representation

IPv4: 32-bit (4-byte) addresses. Address space: ?



IP addresses





IPv4: 32-bit (4-byte) addresses. Address space: 4,294,967,296.



IP addresses





IPv4: 32-bit (4-byte) addresses. Address space: 4,294,967,296. Soonbecomes exhausted → IPv6 (16-byte addresses).



IP addresses






• 207.142.131.235 dot-decimal



IP addresses






• 207.142.131.235 dot-decimal• 0xCF.0x8E.0x83.0xEB dotted-hexadecimal



IP addresses






• 207.142.131.235 dot-decimal• 0xCF.0x8E.0x83.0xEB dotted-hexadecimal• 0317.0216.0203.0353 dotted-octal



Address allocation and ranges




Routing

Selecting paths in a computer network along which to send dataaccording to the IP addresses found in the packet headers. It is afundamental principle of routing that the address encodes informationabout a device’s location within a network (like phone numbers, cf.area codes).




Routing


Some reserved address ranges




Routing



• private network (eg. 10.0.0.0 - 10.255.255.255 ): notroutable outside of the private network and private machinescannot directly communicate with public networks




Routing



• private network (eg. 10.0.0.0 - 10.255.255.255 ): notroutable outside of the private network and private machinescannot directly communicate with public networks

• localhost (127.0.0.0 - 127.255.255.255 ): any addresswithin this range should never appear on an actual network andany packet sent to this address does not leave the sourcecomputer and will count as an incoming packet on that computer(loopback)



Sample non-exam question

We . . .have now our own home LAN. What address range will we usefor our devices? (Well it’s easy to answer). And why?



Name resolution



Name resolution

157.181.67.129

This looks unfamiliar.



Name resolution

157.181.67.129

This looks unfamiliar. How about this (albeit referring to thevery same network device, the SEAS server)?



Name resolution

157.181.67.129


seas3.elte.hu



Name resolution

157.181.67.129


seas3.elte.hu

“Dedicated network devices” are not normally publicly known byIP addresses but by names. This requires translating(resolving) names to IP addresses.



Name resolution

157.181.67.129


seas3.elte.hu

“Dedicated network devices” are not normally publicly known byIP addresses but by names. This requires translating(resolving) names to IP addresses.

Domain Name System (DNS)

It translates domain names (computer hostnames) to IPaddresses.


Network addressing Domain names








7 History



Domain names

seas3.elte.hu



Domain names

seas3.elte.hu

• top-level domain



Domain names

seas3.elte.hu

• felso szintu domén



Domain names

seas3.elte.hu

• top-level domain• subdomains



Domain names

seas3.elte.hu

• top-level domain• aldomének



Domain names

seas3.elte.hu


• second-level domain



Domain names

seas3.elte.hu


• second-level domain• third level domain (a.k.a. host label)



Domain names

seas3.elte.hu


• second-level domain• third level domain (a.k.a. host label)

Top-level domains

• country code top-level domains (ccTLD)• generic top-level domains (gTLD)

• sponsored (.aero.coop.museum. . . )• unsponsored (.info.biz.com.edu.gov. . . )



Homework

Home assigment

What is the IP address of www.example.com?



Domain name assignment

ICANN (Internet Corporation for Assigned Names and Numbers)

Bears overall responsibility for managing the DNS. It controls the rootdomain, delegating control over each top-level domain to a domain nameregistry. For ccTLDs, the domain registry is typically controlled by thegovernment of that country. See www.domain.hu .






Cybersquatting

Registering or using a domain name with bad-faith intent to profit fromthe marketability of a trademark belonging to someone else.






Cybersquatting


Typosquatting

(a.k.a. URL hijacking) a form of cybersquatting which relies on mistakessuch as typographical errors made by Internet users when inputting awebsite address into a web browser.






Cybersquatting


Typosquatting

(a.k.a. URL hijacking) a form of cybersquatting which relies on mistakessuch as typographical errors made by Internet users when inputting awebsite address into a web browser.

Reverse domain hijacking

The practice of acquiring domain names from owners by accusing themof violating trademarks with the domain name, and demanding that thedomain be transferred.



Domain names extra

Unconventional domain names

Combines domain labels (especially the top level domain) to spell outa full user inviting name for a site.



Domain names extra



inter.net



Domain names extra



inter.netdel.icio.us



Domain names extra



inter.netdel.icio.uscr.yp.to



Domain names extra



inter.netdel.icio.uscr.yp.toja.hu



Domain names extra



inter.netdel.icio.uscr.yp.toja.husihu.hu



Domain names extra



inter.netdel.icio.uscr.yp.toja.husihu.hu

Resale of domain names

Huge market for generic names (dot-com era) that even withoutadvertising or marketing attract clients seeking services and productssimply typing in the generic name.business.com : sold for $7.5 million in 1999 (cf. the sex.com story).



Homework

Home assigment

Collect three websites for which their common misspellingsredirect to the correct site, and three others which have somemisspelled URLs hijacked.



Important concepts I.




RFC (Request for Comments)

A set of technical and organizational notes about the Internet. TheInternet Engineering Task Force (IETF) adopts some of the proposalspublished in RFCs as Internet standards (standards track RFCs).






DNS/Name server

The DNS consists of a hierarchical set of DNS servers. Each domainor subdomain has one or more authoritative DNS servers that publishinformation about that domain and the name servers of any domains"beneath" it.






DNS/Name server

The DNS consists of a hierarchical set of DNS servers. Each domainor subdomain has one or more authoritative DNS servers that publishinformation about that domain and the name servers of any domains"beneath" it.

Fully qualified domain name (FQDN)

host label + domain = budling.nytud.hu




Netmask (network mask, subnet mask)

Tells how many bits in IP address octet(s) identify thesubnetwork, and how many bits provide room for hostaddresses.





Tells how many bits in IP address octet(s) identify thesubnetwork, and how many bits provide room for hostaddresses.157.181.67.129 → 255.255.0.0






192.168.2.101 → 255.255.255.0






192.168.2.101 → 255.255.255.0This is information is for the router not for humans. When youhave to manually set it you will be provided with it or you canuse the default for your network.




Gateway

General device to connect two distinct networks. (Our wifirouter is a type of gateway). When connecting two IP-basednetworks (like our home LAN with the ISP’s WAN):




Gateway

General device to connect two distinct networks. (Our wifirouter is a type of gateway). When connecting two IP-basednetworks (like our home LAN with the ISP’s WAN):→ two separate IP address, one on each network




Gateway


• LAN address: the address to which traffic is sent from theLAN




Gateway



• WAN address: the address to which traffic is sent comingfrom the WAN (for our home net it is assigned by the ISP)




Gateway



• WAN address: the address to which traffic is sent comingfrom the WAN (for our home net it is assigned by the ISP)

→ gateway IP address: commonly the LAN address




Gateway — operation





• the addresses of computers on the LAN are hidden behindthe gateway






• the WAN can only see the gateway’s IP address






• the WAN can only see the gateway’s IP address• traffic regulation between the WAN and the LAN: Network

Address Translation (NAT)







Address Translation (NAT)• all of the LAN traffic is presented to the WAN as coming

from the gateway’s WAN IP address







Address Translation (NAT)• all of the LAN traffic is presented to the WAN as coming

from the gateway’s WAN IP address• return WAN traffic is sorted and distributed to the local

network



The assignment of IP addresses




Manual (static IP)

• IP address

• subnet mask

• default gateway

• DNS server(s)

must be specified.




Manual (static IP)

• IP address

• subnet mask

• default gateway

• DNS server(s)

must be specified.

Automatic (dynamic IP)

Dynamic Host Configuration Protocol (DHCP): used bynetworked computers (clients) to obtain unique IP addresses(and all other parameters) from a DHCP server.



Important concepts II.




ServerA computer system that provides services to other computingsystems (clients) over a network. Server can refer to thehardware (heavy-duty irons with constrained user interface)and software (eg. RDBMS).




ServerA computer system that provides services to other computingsystems (clients) over a network. Server can refer to thehardware (heavy-duty irons with constrained user interface)and software (eg. RDBMS).

Client

A computer system that accesses a (remote) service onanother computer by some kind of network. Also can refer tohardware (eg. PC) or software (like a web browser → universalclient).



Feedback slide I.

Sample exam questions



Feedback slide I.


✇ The device that connects two LANs together is a(n)A netmaskB IP addressC network fridgeD gateway



Feedback slide I.


✇ The device that connects two LANs together is a(n)A netmaskB IP addressC network fridgeD gateway ✔



Feedback slide I.



✇ The prebuilt unique identifier of a network device is itsA IP addressB MAC addressC wireless ethernet cardD topology



Feedback slide I.



✇ The prebuilt unique identifier of a network device is itsA IP addressB MAC address ✔

C wireless ethernet cardD topology



Feedback slide I.





Audience questions



Feedback slide I.





Audience questions

• ???



Recap

• computer network

• (wireless) network interface

• MAC address

• modem, access point/router/gateway

• IP address

• domain names, name resolution, DNS• IP assignment:

• static: IP address, netmask, gateway address, DNS server• dynamic: DHCP (server)

• server, client


Network addressing LAN configuration








7 History



Setting up a home LAN

?cable/ADSL modem


Point (AP)

��

Figure: This will hopefully be a working home LAN



Configuring the home LAN — Router




LAN configuration




WAN configuration




WAN configuration

Point-to-Point Protocol over Ethernet• used mainly with ADSL services• offers features as authentication, encryption and compression• provides a classical connection with login and password




Wireless configuration — Set the Service Set Identifier




Wireless configuration — Set the Service Set Identifier

Secure the connection (by default it’s open!)




Tighten access to your AP



Homework

Home assigment

What do the abbreviations WEP, WPA stand for?




We are up and running



Configuring the home LAN — Clients




• There must be some GUI for network configuration, depending onthe OS . . .





like this . . .



Back to the university lab




Sitting in front of a thin client





• no local storage (diskless), minimal local processing






• uses the resources of the host computer (even the OS)







• usually only provides a GUI to a host server








Fat client








Fat client• does not necessarily rely on a server









• has local storage and its own OS









• has local storage and its own OS

• eg.: the PC



Login windows

like this . . .



Login windows




User authentication



User authentication

• User/login name: from a limited set and number ofcharacters



User authentication


• Password: strong/weak (more on week 13)



User authentication


• Password: strong/weak (more on week 13)

When you log in to a diskless client all services/programs areprovided by a host server. In a fat client it may only be yourhome directory that is on a remote machine everything else islocal. Normally it is all hidden behind the user interface.


The Internet and the World Wide Web

The Internet 6= World Wide Web




Internet




Internet• worldwide, publicly accessible network

of interconnected computer networks. . .






• using the standard Internet Protocol(IP), Transmission Control Protocol(TCP) and various applicationprotocols depending on the service(eg. DNS, HTTP, SMTP, POP3 etc.)







• provides many services: eg. DNS,electronic mail, file transfer, instantmessaging, streaming audio and video,online gaming and the World WideWeb








World Wide Web• collection of

interconnecteddocuments, linked byhyperlinksa and URLs

aa reference or navigationelement in a document to anotherresource (document or part of)(week 11)










• most used and known(but just another)service of the Internet











• most used and known(but just another)service of the Internet

• provides easy access toa vast and diverseamount of onlineinformation



The Internet and the World Wide Web The Web








7 History



Operation — Client-server architecture

Accessing a website




Accessing a website

• user types the URL (Uniform Resource Locator) of webpage into a web browser




Accessing a website


• hostname part of URL is resolved into a web server’s IPaddress




Accessing a website



• an HTTP (Hypertext Transfer Protocol) request is sent tothe web server at that IP address, for the page required




Accessing a website



• an HTTP (Hypertext Transfer Protocol) request is sent tothe web server at that IP address, for the page required

• server returns page (file(s)) which is rendered by the webbrowser on the client



The first web pages (1990)



Uniform Resource Identifier (URI)

Compact string of characters used to identify or name a resource.It enables interaction with or access to the resource over a network(typically the web) using specific protocols.





URI (in popular usage → URL) syntax

http︸︷︷︸

scheme

://example.com︸︷︷︸

host

:992︸︷︷︸

port

/animal/bird︸︷︷︸

path

?species=ferret︸︷︷︸

query

# wings︸︷︷︸

fragment





URI (in popular usage → URL) syntax

http︸︷︷︸

scheme

://example.com︸︷︷︸

host

:992︸︷︷︸

port

/animal/bird︸︷︷︸

path

?species=ferret︸︷︷︸

query

# wings︸︷︷︸

fragment

• mailto:[email protected]

• file:///usr/share/dict/words



Operation — the server side




Virtual hosts




Virtual hosts• as a general rule, the IP address and the server name are

interchangeable





interchangeable• problem: there are far more Web sites than servers





interchangeable• problem: there are far more Web sites than servers• in HTTP talk, the client tells the server which name is being used





interchangeable• problem: there are far more Web sites than servers• in HTTP talk, the client tells the server which name is being used• one server with one IP address can provide different sites for

different domain names






different domain names → virtual hosting







telri.nytud.hu has address 193.6.194.149corpus.nytud.hu has address 193.6.194.149







telri.nytud.hu has address 193.6.194.149corpus.nytud.hu has address 193.6.194.149

www is not mandatory in URLsindex.hu has address 217.20.131.2www.index.hu has address 217.20.131.2www.nytud.hu has address 193.6.194.40nytud.hu has address 193.6.194.1



Operation — the client side




Client software — popular browsers

• Mozilla Firefox (all platforms)• Opera (all platforms)• Internet Explorer (Windowses; no longer for Mac OS)• Safari (Mac OS)• lynx (poor man’s CLI browser)




Client software — popular browsers

• Mozilla Firefox (all platforms)• Opera (all platforms)• Internet Explorer (Windowses; no longer for Mac OS)• Safari (Mac OS)• lynx (poor man’s CLI browser)

Customizing your browser — Plugins and extensions

• plugin: application that interacts with the main program within awell defined framework to provide some specific functions

• in browsers: process specific types of files (eg. multimedia, pdf ✌)• in mailers: encrypt or decrypt email (week 13)• in graphic programs: filter and process certain images (week 12)

• extension: modifies or adds to existing functionality (Firefox ✌)




Customizing your browser — Proxies and other settings

• (caching) web proxy: a nearby cache of web pages andfiles available on remote web servers, allowing localnetwork clients to access them more efficiently, quickly orreliably

• cache: a place for temporary storage of data likely to beused again

• other important settings: security, local cache (IE!) etc.




Figure: Setting a web proxy in Firefox



Finding info on the Web

Web portals

An organized pathway to web content, providing various services(news, free email, customization features, chatrooms etc). For manyusers, the starting point of their web browser. (Examples?)




Web portals


Search engines

• programs designed to help efficiently find information stored on acomputer system (language technology may well come into playhere)




Web portals


Search engines


• operation:




Web portals


Search engines


• operation:• web crawling (spider)• indexing• searching: query → relevance ranked result set




Web portals


Search engines



• Examples:




Web portals


Search engines



• Examples:• http://www.webcrawler.com/ (the first, metasearch)• http://www.google.com/ (the most common)• http://search.yahoo.com/




Web portals


Search engines



• Examples:• http://www.webcrawler.com/ (the first, metasearch)• http://www.google.com/ (the most common)• http://search.yahoo.com/• countless others, even for specific purposes s.a. jobs, blogs,

business etc.


Connecting to remote machines Remote login








7 History



Connecting to remote machines — Security

Warning

Whichever way you connect to a remote machine do it in asecure manner:




Warning


• make sure sensitive information (eg. password) travelssecurely → use encrypted connection channels




Warning


• make sure sensitive information (eg. password) travelssecurely → use encrypted connection channels

• all in all, try to avoid unsafe (open) protocols (telnet, FTP,HTTP for confidential web pages), and use SSH, SFTP,SCP, HTTPS instead



Important concepts III.



Important concepts III.

(Software) Port

A virtual data connection that can be used by programs to exchangedata directly (instead of going through a file or other temporary storagelocation). Each data packet header contains a port number to mapdata to a particular process (program) running on a computer. Somecommon port numbers:

20 FTP data21 FTP command22 SSH (6= Social Sciences and Humanities)23 Telnet25 SMTP80 HTTP

110 POP3143 IMAP443 HTTPS993 IMAPS995 POP3S



Feedback slide II.




Feedback slide II.


✇ All in all, the Internet and the World Wide Web are synonymous.• True• False



Feedback slide II.


✇ All in all, the Internet and the World Wide Web are synonymous.• True• False ✔



Feedback slide II.



✇ Which is the odd one out and why? (lead: hw/sw)A ClientB PortC GuiD Server



Feedback slide II.



✇ Which is the odd one out and why? (lead: hw/sw)A ClientB PortC Gui ✔D Server



Feedback slide II.




because . . .



Feedback slide II.




because . . .

Audience questions



Feedback slide II.




because . . .

Audience questions

• What the . . . is a LAN party?



Feedback slide II.




because . . .

Audience questions

• What the . . . is a LAN party?• Now it’s your turn . . .



Connecting to remote machines — GUIs




Virtual Network Computing (VNC)

• a desktop sharing system to remotely control another computer• platform-independent: a VNC viewer on any OS can connect to a

VNC server on any other OS




Virtual Network Computing (VNC)

• a desktop sharing system to remotely control another computer• platform-independent: a VNC viewer on any OS can connect to a

VNC server on any other OS

Remote Desktop Protocol

• allows a user to connect to a(Windows) computer runningMicrosoft Terminal Services

• still in development to enhance itsfunctionality




X Server (Unices)

• allows a user to connect toa computer running an Xdisplay manager

• presents the user with alogin screen to insert theusername and password




Figure: Schematics of a remote X connection



Connecting to remote machines — Poor man’s CLI

SSH connection — putty

• provides secure remote CLI connection in terminal window• can operate with the SSH (Secure Shell) protocol (please use

version 2!)



Connecting to remote machines — Poor man’s CLI

SSH connection — putty

• provides secure remote CLI connection in terminal window• can operate with the SSH (Secure Shell) protocol (please use

version 2!)

Figure: Putty configuration


Connecting to remote machines File transfer








7 History



Transferring files the secure way




SSH File Transfer Protocol (SFTP), Secure Copy Protocol (SCP)

• data is encrypted during transfer• SCP protocol implements file transfers only• SFTP protocol allows for a range of operations on remote files:

resuming interrupted transfers, directory listings, remote fileremoval




SSH File Transfer Protocol (SFTP), Secure Copy Protocol (SCP)

• data is encrypted during transfer• SCP protocol implements file transfers only• SFTP protocol allows for a range of operations on remote files:

resuming interrupted transfers, directory listings, remote fileremoval

Clients: panel based (≈file manager) GUIs

• WinSCP (Windowses)• Fugu (Mac)• all builtin file managers of common desktop environments

(KDE, Gnome) (Linux)




Figure: WinSCP login window




Figure: Remote directory listing in WinSCP


Connecting to remote machines Mailing








7 History



How mail travels through the net




➊ Alice composes amessage using her mailuser agent (MUA). Sends itto recipient’s address.MUA uses Simple MailTransfer Protocol (SMTP)to send message to localmail transfer agent (MTA)(smtp.a.org run by ISP).MTA looks up domainname from destinationaddress (b.org ) in DNS tofind mail exchange serversaccepting messages forthat domain.




➋-➌ DNS server (here for theb.org domain:ns.b.org ), responds withan MX (Mail eXchange)record listing the mailexchange servers for thatdomain (here mx.b.org , aserver run by Bob’s ISP)





☞ elte.hu mail ishandled by 10mx2.mail.elte.hu.





☞ elte.hu mail ishandled by 10mx2.mail.elte.hu.

☞ nytud.hu mail ishandled by 10genesis.nytud.hu.




➍ Alice’s MTA (smtp.a.org )sends the message toBob’s MX server(mx.b.org ) using SMTP,which delivers it to themailbox of the user bob .




➍ Alice’s MTA (smtp.a.org )sends the message toBob’s MX server(mx.b.org ) using SMTP,which delivers it to themailbox of the user bob .

☞ telnetgenesis.nytud.hu 25. . .




telnet genesis.nytud.hu 25Trying 193.6.194.37...Connected to genesis.nytud.hu (193.6.194.37).Escape character is ’ˆ]’.220 genesis.nytud.hu ESMTP Sendmail 8.13.1/8.13.1;Sun, 15 Oct 2006 12:05:04 +0200HELO ny01.nytud.hu250 genesis.nytud.hu Hello ny01.nytud.hu[193.6.194.1], pleased to meet youMAIL FROM:<[email protected]>250 2.1.0 <[email protected]>... Sender okRCPT TO:<[email protected]>250 2.1.5 <[email protected]>... Recipient okDATA354 Enter mail, end with "." on a line by itselfFollow your dreams, You can reach your goals, I’mliving proof! Beefcake!.250 2.0.0 k9FA5491002427 Message accepted fordeliveryquit221 2.0.0 genesis.nytud.hu closing connectionConnection closed by foreign host.




➎ Bob presses the "get mail"button in his MUA, whichpicks up the messageusing the Post OfficeProtocol (POP3).




➎ Bob presses the "get mail"button in his MUA, whichpicks up the messageusing the Post OfficeProtocol (POP3).

☞ From [email protected] Oct 15 12:08:122006 . . .



How mail travels through the netFrom [email protected] Sun Oct 15 12:08:12 2006Return-Path: <[email protected]>Received: from genesis.nytud.hu (genesis.nytud.hu [193. 6.194.37])

by ny01.nytud.hu (8.11.6/8.11.6) with ESMTP id k9FA8A4178 59for <[email protected]>; Sun, 15 Oct 2006 12:08:10 +0200

Received: from ny01.nytud.hu (ny01.nytud.hu [193.6.194. 1])by genesis.nytud.hu (8.13.1/8.13.1) with SMTP id k9FA5491 002427for <[email protected]>; Sun, 15 Oct 2006 12:06:06 +0200

Date: Sun, 15 Oct 2006 12:05:04 +0200From: [email protected]: <[email protected] ud.hu>Content-Type: TEXT/PLAIN; charset=US-ASCIIX-AntiVirus: scanned for viruses by AMaViS 0.2.1 (http://a mavis.org/)X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on ny01.nytud.huX-Spam-Level:X-Spam-Status: No, hits=0.3 required=6.5 tests=NO_REAL_ NAME autolearn=no

version=2.63

Follow your dreams, You can reach your goals,I’m living proof! Beefcake!



Internet e-mail format




Header

From: e-mail address (and name) of the senderTo: e-mail addresses (and names) of the receiver

Subject: brief summary lineDate: local time and date when message was originally sent

Cc: courtesy/carbon copyBcc: blind carbon copy; contains addresses of recipients of the

message whose addresses are not to be revealed to otherrecipients

Content-Type: information about how the message has to be displayed(MIMEa type)

aMultipurpose Internet Mail Extensions eg. Content-Type: image/gif;




Header







Blank line




Header







Blank line

Body: the message

• e-mail was originally designed for 7-bit ASCII• many mail transport agents still don’t support 8 bit transfer• content transfer encodings to encode 8 bit data for transmission:

quoted printable, base64 (handled by your MUA)



An encoded binary attachment

------=_NextPart_000_00FE_01C65FE0.4FD94570Content-Type: application/msword;

name="hasznositasi_lehetosegek.doc"Content-Transfer-Encoding: base64Content-Disposition: attachment;

filename="hasznositasi_lehetosegek.doc"

0M8R4KGxGuEAAAAAAAAAAAAAAAAAAAAAPgADAP7/CQAGAAAAAAAAAAAAAAABAAAAQgAAAAAAAAAAEAAARAAAAAEAAAD+////AAAAAEMAAAD//////////////////// //////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////// ////////////////////////s/////////////////////////////////////////////////// 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



Variations on the mailing theme




Webmail instead of MUA✔ a web application that allow users to access their e-mail through a web

browser✔ accessible anywhere with an internet connection and a web browser✔ ensures a permanent address (change of ISP → end of mail service and

address at ISP!)✘ limited e-mail storage space, advertisements displayed• Hotmail, Yahoo!Mail, Gmail, Freemail etc. ✌




Webmail instead of MUA✔ a web application that allow users to access their e-mail through a web

browser✔ accessible anywhere with an internet connection and a web browser✔ ensures a permanent address (change of ISP → end of mail service and

address at ISP!)✘ limited e-mail storage space, advertisements displayed• Hotmail, Yahoo!Mail, Gmail, Freemail etc. ✌

Internet Message Access Protocol (IMAP) instead of POP3

Both allow a local client to access e-mail on a remote server. For and againstIMAP:

✔ both connected and disconnected modes of operation✔ multiple clients can simultaneously connect to the same mailbox✔ multiple mailboxes (folders) on the server✘ very complicated protocol (today no problem, so use this over POP3 if

possible)



Important concepts IV.




Mailbox

The (local or remote) store of your messages. Standard types:

• maildir: a directory where each message is a separate file• mbox: a single file with all messages concatenated

➥ From [email protected] Sun Oct 15 12:08:12 2006




Mailbox

The (local or remote) store of your messages. Standard types:

• maildir: a directory where each message is a separate file• mbox: a single file with all messages concatenated

➥ From [email protected] Sun Oct 15 12:08:12 2006

Folder

A mailbox (file) for specific types of messages. Standard types offeredby most MUAs include:

• Inbox: default place for incoming messages• Sent: for a copy of messages you send• Drafts: placeholder for messages under composition• Trash: backup folder for deleted messages



MUAs and their basic commands




Popular graphical MUAs

• Mozilla Thunderbird (all platforms)

• Tiger Mail (Mac)

• Outlook Express (Windowses, Mac) . . . and countlessothers




Popular graphical MUAs

• Mozilla Thunderbird (all platforms)

• Tiger Mail (Mac)

• Outlook Express (Windowses, Mac) . . . and countlessothers

Basic commands• get mail

• write/compose (→ attach)

• send

• reply (all)

• forward, bounce

• delete ✌



Setting up a MUA for remote mail service



Setting up a MUA for remote mail service

General account settings Mail server settings



Local MUAs on servers with own MTA



Local MUAs on servers with own MTA

Local access to mailboxes• normally for users of servers with unrestricted access• possible with GUI MUAs but the typical scenario is to log in

to a server through a CLI and starting some CLI mail client• pine• mutt• elm

• some of them are very powerful (pine, mutt) and offermuch the same functionality as GUI MUAs



Humble CLI mail client

Mailbox is ’/var/spool/mail/oravecz’ with 1858 messages [ ELM 2.5 PL6]

N 1 Oct 15 *** / [email protected] (19)NM 3 Oct 15 (Undisclosed) nyelveszForumAdmin (65) Téma érte sítésO 175 Jul 29 Corpora / John F. Sowa (98) Re: [Corpora-List] ANCO 176 Jul 29 Corpora / Nicholas Sanders (82) Re: [Corpora-Lis t] ANCO 177 Jul 28 Corpora / John F. Sowa (84) Re: [Corpora-List] ANCO 178 Jul 28 Corpora / Nicholas Sanders (77) [Corpora-List] R e: ANCO 179 Jul 28 Corpora / Nicholas Sanders (77) Re: [Corpora-Lis t] ANCO 180 Jul 28 Corpora / FIDELHOLTZ_DOOCHIN (85) [Corpora-Lis t] Re: ANC

|=pipe, !=shell, ?=help, <n>=set current to n, /=search pat terna)lias, C)opy, c)hange folder, d)elete, e)dit, f)orward, g )roup reply, m)ail,

n)ext, o)ptions, p)rint, q)uit, r)eply, s)ave, t)ag, u)nde lete, or e(x)it

Command:



Filtering incoming mail — MDAs

Mail Delivery Agent (MDA)





• program that accepts incoming e-mail messages andperforms certain actions over them like






• sorting messages into different folders






• sorting messages into different folders• forwarding messages






• sorting messages into different folders• forwarding messages• labeling messages






• sorting messages into different folders• forwarding messages• labeling messages• deleting messages etc.







with the help of filter rules that match on sections ofmessage header.







with the help of filter rules that match on sections ofmessage header.

• most GUI MUAs have this as built in functionality ✌



Filtering incoming mail — spams




Spam

Unsolicited messages to many recipients, the electronicequivalent of junk mail (week 13). To avoid:




Spam


• use some automated e-mail filtering program




Spam



• ask the system administrator to trap it at the mail serverlevel




Spam




• don’t publish your e-mail address at open websites withnormal syntax (use address munging)




Spam




• don’t publish your e-mail address at open websites withnormal syntax (use address munging)[email protected]




Spam




• don’t publish your e-mail address at open websites withnormal syntax (use address munging)[email protected] ✘




Spam





cartman-kukac-mit-edu




Spam





cartman-kukac-mit-edu ✔


Connecting to remote machines Mailing list, newsgroups, forums








7 History



Mailing lists, newsgroups and discussion forums




Mailing lists




Mailing lists

• a list of e-mail addresses




Mailing lists

• a list of e-mail addresses• subscribers receiving mail at those addresses




Mailing lists

• a list of e-mail addresses• subscribers receiving mail at those addresses• reflector: a single e-mail address that sends a copy of the

message to all of the subscribers




Mailing lists


message to all of the subscribers• server/program operated service; additional e-mail addresses

for administration




Mailing lists



for administration

Types




Mailing lists



for administration

Types

• announcement list: one-way information; can only be postedto by selected people




Mailing lists



for administration

Types


• discussion list: any subscriber may post




Mailing lists



for administration

Types


• discussion list: any subscriber may post• moderated list: every message must be approved by a

moderator




Newsgroups




Newsgroups

• a repository for a discussion group (orginally within the Usenetsystem) for messages posted from many users




Newsgroups


• arranged into (dot.sep.a.rated ) hierarchies to find relatedgroups easily




Newsgroups



• distributed by dedicated news servers using the NetworkNews Transfer Protocol (NNTP – port 119)




Newsgroups




Usenet (USEr NETwork)




Newsgroups





• a global, distributed Internet discussion system




Newsgroups





• a global, distributed Internet discussion system• worldwide newsgroups are organized within nine hierarchies,

eight of which work under consensual guidelines aboutadministration and naming




Newsgroups





• a global, distributed Internet discussion system• worldwide newsgroups are organized within nine hierarchies,

eight of which work under consensual guidelines aboutadministration and naming

• creation of a new newsgroup under the Big 8 is a Big-8Management Board controlled procedure



The Big 8

comp. * computer-related discussionsmisc. * Miscellaneous topicsnews. * Discussions and announcements about Usenetrec. * Recreation and entertainmentsci. * Science related discussionssoc. * Social discussionstalk. * Talk about various topicshumanities. * Fine arts, literature, philosophy

Table: The Big 8 top hierarchies



The Big 8



• alt.*: the big 9th but not controlled



The Big 8



• alt.*: the big 9th but not controlled• other hierarchies (regional, language-specific), local news

service ✌



Discussion forums

Internet forum



Discussion forums

Internet forum• a WWW facility for holding discussions



Discussion forums


• also the software providing the facility



Discussion forums



• essentially a website composed of a number ofmember-written threads



Discussion forums




• user, registration, moderator, administrator



Discussion forums





• wide range of topics



Discussion forums






• allows anyone to reply to an existing or create a new thread



Discussion forums







• e-mail notification



Discussion forums







• e-mail notification

• good place to find an answer to very obscure questionssuch as how to fix a particular computer problem


Connecting to remote machines Other social netfacilities








7 History



Real time communication

Instant messaging




Instant messaging

• real-time communication between two or more peoplebased on typed text




Instant messaging


• requires the use of a client program that connects to aninstant messaging service




Instant messaging



• contact list: people currently online and available to chat




Instant messaging




• status message: ≈ message on a telephone answeringmachine




Instant messaging




• status message: ≈ message on a telephone answeringmachine

• .NET Messenger Service, AOL Instant Messenger, GoogleTalk, iChat, ICQ, Jabber, Qnext, QQ, Skype, Yahoo!Messenger, talk




Chat rooms




Chat rooms• Internet Relay Chat (IRC)





• text based group (many-to-many) communication indiscussion channels






• private messaging is also allowed






• private messaging is also allowed• client-server; Xchat, Bersirc, ChatZilla, Opera






• private messaging is also allowed• client-server; Xchat, Bersirc, ChatZilla, Opera• channel/user modes: moderated; i nvisible etc.






• private messaging is also allowed• client-server; Xchat, Bersirc, ChatZilla, Opera• channel/user modes: moderated; i nvisible etc.• IRC bot: a program that connects as a client and performs

special services (managing channels, logging, giving outinformation on demand, creating statistics etc.)








• 2D visual chat rooms: a graphic representation of the user(avatar) movable around a graphic background of the room








• 2D visual chat rooms: a graphic representation of the user(avatar) movable around a graphic background of the room

• 3D chat rooms utilize 3D graphics, allow users to build theirown spaces



Blogs and Wikis

Web log



Blogs and Wikis

Web log

• online journal evolved from online diary



Blogs and Wikis

Web log


• frequent, chronological publication of personal thoughts



Blogs and Wikis

Web log



• can be written by one person or a group of contributors



Blogs and Wikis

Web log




Wiki wiki



Blogs and Wikis

Web log




Wiki wiki• online collaboration model and tool that allows any user to

edit some content of webpages through a simple browser



Blogs and Wikis

Web log






• does not require users to know HTML (week 11) but writtenin a simple markup language



Blogs and Wikis

Web log







• wikitext: source format



Blogs and Wikis

Web log







• wikitext: source format

Learn them by use.



Feedback slide III.




Feedback slide III.


✇ A primary difference between forums and mailing lists is thatA the former operates over the Internet while the latter is localB the latter automatically delivers new messages to subscribers while

the former normally requires the user to check for thisC the former might be moderated, the latter neverD the latter is operated by a dedicated program, the former is

operated by a web browser



Feedback slide III.



the former normally requires the user to check for this ✔

C the former might be moderated, the latter neverD the latter is operated by a dedicated program, the former is

operated by a web browser



Feedback slide III.





operated by a web browser✇ The standard client to read newsgroup posts is the Firefox web

browser.• True• False



Feedback slide III.






browser.• True• False ✔



Feedback slide III.







Audience questions



Feedback slide III.







Audience questions

• ???


Connecting to remote machines Netiquette








7 History



Netiquette



Netiquette

Internet etiquette

Conventions of politeness recognized on Usenet, in mailing lists,and on other electronic forums.



Netiquette

Internet etiquette


Newsgroups:



Netiquette

Internet etiquette


Newsgroups:• think before you post



Netiquette

Internet etiquette


Newsgroups:• think before you post• quote interspersed, with your response following the relevant

quoted material (and only the relelvant!)



Netiquette

Internet etiquette



quoted material (and only the relelvant!)• to express irony, sarcasm etc. use but do not overuse

emoticons



Netiquette

Internet etiquette




emoticons• post in plain text



Netiquette

Internet etiquette




emoticons• post in plain text• before asking a question, read the messages already in the

group and read the group’s FAQ



Netiquette

Internet etiquette




emoticons• post in plain text• before asking a question, read the messages already in the

group and read the group’s FAQ• keep flames under control, don’t be a troll or off-topic



Netiquette

Internet etiquette

Forums:



Netiquette

Internet etiquette

Forums:• read any rules and guidelines established by the community



Netiquette

Internet etiquette

Forums:• read any rules and guidelines established by the community• before creating a new topic thread, search to see if a similar

topic already exists



Netiquette

Internet etiquette


topic already exists• follow standard grammar/spelling rules and don’t use slang



Netiquette

Internet etiquette


topic already exists• follow standard grammar/spelling rules and don’t use slang• post in the correct forum category



Netiquette

Internet etiquette


topic already exists• follow standard grammar/spelling rules and don’t use slang• post in the correct forum category• don’t double post



Netiquette

Internet etiquette



Recommended practice is . . .



Netiquette

Internet etiquette



Recommended practice is . . .• to read RFC 1855 (Netiquette Guidelines)



Netiquette

Internet etiquette



Recommended practice is . . .• to read RFC 1855 (Netiquette Guidelines)• to educate yourself in the matter (GIYF)



Homework

Home assigment

What do the abbreviations EOD, FGI, FYI, GIYF, GLOG, RTFM,UTFW stand for? Do some backround research on Internetslang.


History

Homework

Home assigment

Do some background reading on the history of the Internet (cf.ARPANET) and the Web.


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