Internet Programming. Internet Technology Networking Basics Internet Basics Internet Protocol TCP Applications.

Internet Programming

Internet Technology

Networking Basics

Internet Basics

Internet Protocol

TCP

Applications

Circuit Switching

Internet design:

Smarts at the edges& simple core

Packet Switching

Packet Switching

Key Ideas

Simple

Stateless Core

Unreliable

Packets may be dropped(e.g., to handle congestion)

Flexible

Packets may take any route

Simple

Unreliable

Flexible

Robust

End to end principle

en.wikipedia.org/wiki/End-to-end_principle

“End-to-End Arguments in System Design”,

Saltzer, J., Reed, D., and Clark, D.D.

Simple Core

all the core has to do is route packets

simple: using only local information

each router has a routing table

chooses the next hop by destination

like sending a letter...

Like sending a letter

Willem de Bruijn

De Boelelaan 1081

1081 HV Amsterdam

NetherlandsNational Postal Center

Amsterdam Post OfficeVrije Universiteit

My mailbox

Smart Edges

server: provider of a service client: consumer of a service

a web client a.k.a. browser (e.g. IE, Firefox) retrieving pages from a web server (e.g. Apache)

a mail client (e.g. Outlook) retrieving e-mail from a mail server (e.g. Exchange)

Internet Technology

Networking Basics

Internet Basics

Internet Protocol

TCP

Applications

Idea

"For each of these three terminals, I had three different sets of user commands. So if I was talking online with someone at S.D.C. and I wanted to talk to someone I knew at Berkeley or M.I.T. about this, I had to get up from the S.D.C. terminal, go over and log into the other terminal and get in touch with them. [...] I said, it's obvious what to do (But I don't want to do it): If you have these three terminals, there ought to be one terminal that goes anywhere you want to go where you have interactive computing. That idea is the ARPAnet."

—Robert W. Taylor, co-writer "The Computer as a Communications Device", in an interview with the New York Times, [2]

History

1969: ARPANetPacket Switching: Robust

History

1984: NFSNetNational USA University network with dial-up

(other TCP/IP networks within the military)

History

2005: an Internet snapshot

Network of Networks

Commercial CarriersHome router + 2 computers

Community Networks

Community Wifi (e.g., mesh networks)

Peering: Internetworking

Interconnection of 2+ Autonomous Systems (ASs)Exchange routing information with BGP

Transit (for pay)Peer (tit for tat)

Incentive to peer directly with more networks: less transit

Public (AMS-IX) or Private

Explicit contracts

Multiple Levels

Tier 1 “A network that can reach every other network on the Internet without purchasing IP

transit or paying settlements." (only 8)

Tier 3 ~= non-multihomed end-user

Example: SAVVIS: Tier 2 with private backbone

Wireless Community Networks

Border Gateway Protocol (BGP)

Periodic route table exchanges

A.1 – B.1 – B.2 – C.1 – C.2 – D.1

B.1->A.1 : connect B, C(B), D(B,C)B.1 -> B.2 : connect A

Automatically updates local router's tablesMultihome automatic failover, etc.

ASN

Organization

Robust because decentralized?

DNS Root ServersIANA numbers

ICANN Root level TLDs

Standards: IETF (RFCs), W3C

Internet Technology

Networking Basics

Internet Basics

Internet Protocol

TCP

Applications

Internet Protocol (v4)

Basic end-to-end Connectivity

Internet addresses Internet Protocol (IP) Addresses

Every node has a unique numeric address

Form: 32-bit binary number New standard, IPv6, has 128 bits (1998)

Organizations are assigned groups of IP addresses for their computers

130.37.192.19 (client)

130.37.20.20(server)

(www.cs.vu.nl)

Clients and servers

www.cs.vu.nl

www.cs.vu.nl = 130.37.20.20

nameserver

What’s a protocol?

Hi

Hi

Got thetime?2:00

TCP connection requestTCP connectionresponse

Get http://www.cs.vu.nl/~herbertb

<file>

time

Network Technology

Topic of another class!

Internetwork Technology: TCP/IP

Will discuss only what we need for now

SMTP, HTTP, DNS

UDP, TCPInternet Protocol (v4)

Packet Switching in Practice

Packet Switching and Protocols

An IP packet

DATA

Missing

ConnectionsReliability

Packet Ordering

Congestion Control

Internet Technology

Networking Basics

Internet Basics

Internet Protocol

TCP

Applications

Transmission Control Protocol (TCP)

ReliabilityPacket Ordering

Connections

Congestion Control

Reliability

Resend packets that are lost underway

Reliability

ACK packets

Timeout

Retransmit

Ordered Data

Packets may travel at different speedReestablish order at arrival (buffer)

Connections

Ordered, reliable bytestream+

Reliable open and close

“Three way handshake”

Internet Technology

Networking Basics

Internet Basics

Internet Protocol

TCP

Applications

Domain Name System (DNS)

Lookup IP address127.0.0.1

By human readable namewww.google.com.(note the last dot!)

Domain Name System (DNS)

Hierarchical Distributed System

Hierarchical Names

Domain Name System (DNS)

Let us trace a connection

DNS: nslookup contacts the (distributed) Internet name service

nslookup www.few.vu.nl

IP: traceroute allows us to find the path tracert www.few.vu.nl

nslookup

% nslookup www.few.vu.nlServer: 130.37.20.3

Address: 130.37.20.3#53

Non-authoritative answer:

www.few.vu.nl canonical name = soling.few.vu.nl.

Name: soling-public.few.vu.nl

Address: 130.37.20.20

Application Protocols

DNS!FTP: File transferNTP: Time SynchronizationTelnet: Terminal accessSSH: Secure terminal accessXMPP: MessagingSMTP: EmailHTTP: Web (Next lecture)

Email

Network

PushPush

Pull

smtp.few.vu.nl

mail.receiver.org

SMTPSMTP

IMAP,POP

IMAP,POP

HTTP

Simple Mail Transfer Protocol

Store and Forward network

Simple? Example ...

S: 220 smtp.example.com ESMTP PostfixC: HELO relay.example.orgS: 250 Hello relay.example.org, I am glad to meet youC: MAIL FROM:<[email protected]>S: 250 OkC: RCPT TO:<[email protected]>S: 250 OkC: RCPT TO:<[email protected]>S: 250 OkC: DATAS: 354 End data with <CR><LF>.<CR><LF>C: From: "Bob Example" <[email protected]>C: To: Alice Example <[email protected]>C: Cc: [email protected]: Date: Tue, 15 Jan 2008 16:02:43 -0500C: Subject: Test messageC:C: Hello Alice.C: This is a test messageC: .S: 250 Ok: queued as 12345C: QUITS: 221 Bye{The server closes the connection}

Received: from mail.vu.nl (mail.vu.nl [130.37.129.161])

by tornado.few.vu.nl for <[email protected]>; Wed, 3 Dec 2008 10:59 +0100

Received: from DIENSTEX1.dienst.ad.vu.nl (mail.dienst.vu.nl [130.37.136.125])

by mail.vu.nl (8.12.11.20060308/8.12.11) for <[email protected]>; Wed, 3 Dec 2008 10:59:56 +0100

Email (1/2)

Email (2/2)MIME-Version: 1.0Content-Type: multipart/alternative; boundary="----_=_NextPart_001_01C9552D.E50A028F"Subject: Visum is binnenDate: Wed, 3 Dec 2008 10:59:56 +0100From: "Eek, D" <[email protected]>To: "Willem de Bruijn" <[email protected]>

This is a multi-part message in MIME format.

------_=_NextPart_001_01C9552D.E50A028FContent-Type: text/plain;

charset="us-ascii"Content-Transfer-Encoding: quoted-printable

Goedemorgen Willem,=20Wij hebben je paspoort met visum terug ontvangen van het visumbureau.

Reception

POP3: Post Office ProtocolFetch data from a directory: store at homeStateless

Aside from optional 'read items' hash

IMAP4: Internet Message Access Protocol`remote folders': store on serverStatefulConcurrent access

WebmailProprietary method on top of HTTPFrequently uses IMAP between webserver and mailserver

Multipurpose Internet Mail Extensions

Send more than 7bit ASCII text:Binary (images), Non-latin script

Identify encoding, e.g.,quoted-printable: =[HEX][HEX] for instance, =20 means space

Break up messages html+imgtext/html

Also used elsewhere (such as webservers)

Mime content encodings

=B7Hola, se=F1or!

is interpreted as

¡Hola, señor!.

Mime content-type=

text/plaintext/html

image/jpegvideo/mpeg2

...application/octet-stream

Mime special content-type=

message/rfc822multipart/alternativemultipart/form-data

...

many more. Official list atwww.iana.org/assignments/media-types/

SMTP Security

From: spoofing

Man in the middle can sniff and change data

Open Relay

SPAM

SMTP SecurityCounteraction difficult

Network Effect

AuthenticationPGP

ensure contents integrity (sig/enc)

DomainKeys Identified Mail (DKIM)Guard against spoofing, indirectlySender/Server RSA SIGPublic Key through sender domain DNSUsed by Yahoo! and Google.Does not guard the envelop

Your post advocates a

( ) technical ( ) legislative ( ) market-based ( ) vigilante

approach to fighting spam. Your idea will not work. Here is why it won't work. (One or more of the following may apply to your particular idea, and it may have other flaws which used to vary from state to state before a bad federal law was

passed.)

[...]

Fighting SPAM

( ) Spammers can easily use it to harvest email addresses( ) Mailing lists and other legitimate email uses would be affected( ) No one will be able to find the guy or collect the money( ) It is defenseless against brute force attacks( ) It will stop spam for two weeks and then we'll be stuck with it( ) Users of email will not put up with it( ) Microsoft will not put up with it( ) The police will not put up with it( ) Requires too much cooperation from spammers( ) Requires immediate total cooperation from everybody at once( ) Many email users cannot afford to lose business or alienate potential employers( ) Spammers don't care about invalid addresses in their lists( ) Anyone could anonymously destroy anyone else's career or business

Specifically, your plan fails to account for

( ) Laws expressly prohibiting it( ) Lack of centrally controlling authority for email( ) Open relays in foreign countries( ) Ease of searching tiny alphanumeric address space of all email addresses( ) Asshats

Internet Technology Exam MaterialNetworking Basics

circuit vs. packet switchingend-to-end argumentclient/server programming

Internet Basicsnetwork of networkspeering

IPprotocol stack

TCPreliability, ordering, conn.

DNSEmail

push vs. pull, mime, authenticationbasic smtp

Internet Technology Practical

Trace a Route with tracert.exe

Lookup a domain name with nslookup.exe

Send me an email manually using putty

Don't forget: come up with a website plan for tomorrow!

Flow Control

Buffering: sliding window

Congestion Control

Scale sliding window sizeAutomatic, based on transport quality

Additive Increase, Multiplicative Decrease

Bandwidth Delay Product

Maximal bandwidth of a TCP stream depends onphysical bandwidth, but also:

congestion control protocolroundtrip time