Networking

November 8, 2001

Administrivia

• Homework 5 is due on Tuesday• Homework 6 will be due next Tuesday

• If you need help, are concerned about midterm grade, want to chat, …– Talk to TA’s– Talk to me– To set up time,

• Send email• Talk to me after class

Where we are

• We built a computer• We built an operating system to control our

computer • Next, let’s connect our computer to a bigger

network• Why??

Where we are

• We built a computer

• We built an operating system to control our computer

• Next, let’s connect our computer to a bigger network

• Why??– Email

– Chat

– Web

– Shared Files

– Shared CPUs

Communications methods

• Email– I send something to your server– You get it from your server

• Chat– We both send messages to a server at the same time

• Web– I interact with something you put on the server

• Shared Files– I use things that are on your disk

• Shared CPUs– I run a program on your CPU

The network(s)

• There is a local network where – I connect to my server– I connect to other machines in my local

network

• There is a larger network where – I connect to your server– I connect to your machine

Your local network

• Princeton.edu• You use a machine in princeton.edu

– Machine has a name and a number• princeton.edu (128.112.128.81) • cs.princeton.edu (128.112.136.10)• voronoi.cs.princeton.edu (128.112.104.237) • Princeton.edu is 128.112.0.0 -

128.112.255.255

• You mount files from another machine as your F: drive (UNIX account)

Moving beyond your local network

• The mailer on your machine is set up to be a client of the Princeton mail server– mail.princeton.edu 128.112.129.14

• If you send mail to cs111@princeton.edu– The server keeps the mail for the cs111 account

• If you send mail to cs111@cs.princeton.edu– The server sends the mail to the Princeton-cs mail

server mail.cs.princeton.edu (128.112.136.7)

– That server keeps the mail for its cs111 account

Communications between servers

• A server has ports for other machines– Port 25 is outgoing mail server– Port 993 is incoming mail server– Port 80 is http server– …

• Protocols define how communications work– E.g. http: HyperText Transfer Protocol

Sidebar - What can be broadcast

• The Friend Center

• Times Square

• Baby Kimberly

• Many Earthcams

Networks – Some buzzwords

• WANs vs LANs– My Local Area Network (the Local Ethernet)– The Wide Area Network (Internet)

• Protocols– TCP/IP– SLIP/PPP

• Routers• Firewalls

Simple task – email to your uncle

• Use my modem to connect to my Internet Service Provider (ISP)

• My ISP decides whether the email is in its local area network (LAN) or in the wide area network (WAN) – the internet

• Handoff (possibly via internet) to his ISP

• His ISP delivers mail to him

Courtesy ofhttp://home.about.com/

Communication pieces

• Modem (Modulator DeModulator) – Converts digital to analog for transfer over phone lines– Speed measured in baud (bits/second) 57.6Kb (might compress)– Communication via X.25 protocol– Allows for PPP/SLIP connection to network

• Ethernet (for Local Area Network (LAN))– Uses coaxial cable– Speed measured in Mb (million bits/second), 10/100 Mb common– Everyone on same wire, need backoff strategy for collision

• Repeater– Enhances signals

Communication pieces (cont.)

• Wide Area Network (WAN)– Network that is broader than local– Will include many LAN’s

• Router– Does traffic control between networks

• Token ring– Other communication network– First get permission, then send information

Communication pieces (cont.)

• Gateway– Specialized router that does conversion– Functionally similar to modem (w/ routing)

• Firewall– Establish control policies– Filters packets going in/out

Getting to my uncle

traceroute to yahoo.com (216.115.108.245), 30 hops max, 38 byte packets 1 aegis (128.112.168.6) 2.247 ms 1.581 ms 1.265 ms 2 csgate.CS.Princeton.EDU (128.112.152.1) 2.924 ms 1.468 ms 1.586 ms 3 vgate1.Princeton.EDU (128.112.128.114) 2.169 ms 1.740 ms 1.587 ms 4 tcggate.Princeton.EDU (128.112.60.11) 1.905 ms 2.272 ms 2.382 ms 5 12.124.192.5 (12.124.192.5) 3.880 ms 3.366 ms 4.177 ms 6 gbr1-p50.phlpa.ip.att.net (12.123.137.6) 3.754 ms 3.589 ms 4.178 ms 7 gbr4-p20.n54ny.ip.att.net (12.122.2.17) 6.917 ms 7.018 ms 6.201 ms 8 ggr1-p370.n54ny.ip.att.net (12.123.1.125) 7.859 ms 6.509 ms 7.153 ms 9 pos1-1.core2.NewYork1.Level3.net (63.211.54.65) 7.112 ms 7.034 ms 7.876 ms10 ae0-51.mp1.NewYork1.Level3.net (64.159.17.1) 7.715 ms 7.881 ms 6.762 ms11 so-2-0-0.mp2.SanJose1.Level3.net (64.159.0.218) 95.444 ms 99.435 ms 95.818 ms12 gigabitethernet10-2.ipcolo4.SanJose1.Level3.net (64.159.2.170) 97.369 ms 96.741 ms 98.004 ms

13 * * *14 ge-3-3-0.msr1.pao.yahoo.com (216.115.101.42) 97.107 ms 97.919 ms 97.152 ms15 vlan29.bas2-m.snv.yahoo.com (216.115.100.126) 210.069 ms 98.263 ms 98.367 ms16 img5.yahoo.com (216.115.108.245) 98.169 ms 99.370 ms 98.838 ms

Getting to my uncle – leaving PU

traceroute to yahoo.com (216.115.108.245), 30 hops max, 40 byte packets

1 aegis (128.112.168.6) 2.247 ms 1.581 ms 1.265 ms

2 csgate.CS.Princeton.EDU (128.112.152.1) 2.924 ms 1.468 ms 1.586 ms

3 vgate1.Princeton.EDU (128.112.128.114) 2.169 ms 1.740 ms 1.587 ms

4 tcggate.Princeton.EDU (128.112.60.11) 1.905 ms 2.272 ms 2.382 ms

Getting to my uncle – in my ISP

5 12.124.192.5 (12.124.192.5) 3.880 ms 3.366 ms 4.177 ms

6 gbr1-p50.phlpa.ip.att.net (12.123.137.6) 3.754 ms 3.589 ms 4.178 ms

7 gbr4-p20.n54ny.ip.att.net (12.122.2.17) 6.917 ms 7.018 ms 6.201 ms

8 ggr1-p370.n54ny.ip.att.net (12.123.1.125) 7.859 ms 6.509 ms 7.153 ms

Signal leaves Princeton, goes to Philadelphia and then to New York

After the handoff

9 pos1-1.core2.NewYork1.Level3.net (63.211.54.65) 7.112 ms 7.034 ms 7.876 ms

10 ae0-51.mp1.NewYork1.Level3.net (64.159.17.1) 7.715 ms 7.881 ms 6.762 ms

11 so-2-0-0.mp2.SanJose1.Level3.net (64.159.0.218) 95.444 ms 99.435 ms 95.818 ms

12 gigabitethernet10-2.ipcolo4.SanJose1.Level3.net (64.159.2.170) 97.369 ms 96.741 ms 98.004 ms

Signal crosses the country in his ISP

Sidebar on speed

• It takes us – 6.762 ms to get to New York (this is .006762 seconds)

– 95.444 ms to get to San Jose

• Takes 88.682 ms to get from New York to San Jose

• Distance from New York to San Jose is 2558 miles

• Light needs .0137526881 seconds to travel that distance

• Our signal goes there and back– 1 way takes .044341 seconds

• System is running at about 30% of its ultimate limit

What do the numbers mean

• IP (Internet Protocol) numbers– a.b.c.d where each of a,b,c,d is a byte (number 0-255)

• Unique identifiers• May correspond to names.

– Numbers more accurate

• Can build subnets by fixing upper bytes– In the address 192.114.36.91

• 192.114.36 is the host's subnet identifier

• 91 is the host's number on that subnet

Levels of the internet

1. Physical 

2. Data Link

3. Network

4. Transport

5. Session

6. Presentation

7. Application

Levels of the internet

1. Physical Basic hardware components for networks.  Wire from modem to machine,

….

2. Data LinkFormat of frames (how data is to be put together) e.g. bit/byte stuffing,

checksum

3. NetworkAddress assignment, Packet's forwarding methods ARP (Address Resolution  Protocol) used to map an IP address into a

hardware address.

4. TransportTCP (Transmission  Control  Protocol) protocol for the transfer of packets of data to a remote computer. Packets are guaranteed to arrive and in the correct order.

Levels of the internet

5. SessionEstablishing a communication session, Security, Authentication  i.e.

passwords

6. PresentationComputers represent data in different ways (char, integer) thus the protocol

need to translate the data to and from the local node.

7. ApplicationSpecifications for applications using the network, how to send a request, how

to specify a filename over the net, how to respond to a request etc..

TCP/IP

Other protocols

• FTP   File Transfer Protocol – FTP enables transferring of text and binary files over TCP connection.

• Telnet   – Telnet is a terminal emulation protocol for use over a TCP connection. It

enables users to login to remote hosts

• SMTP Simple Mail Transfer Protocol -  – This protocol is dedicated for  sending EMail messages over a TCP

connection.

• HTTP Hyper Text Transport Protocol -  – A protocol used to transfer hypertext pages across the world wide web.

• SNMP Simple Network Management Protocol -  – A simple protocol that defines messages related to network management.

SNMP allows network devices (e.g. routers) to be configured by any host on the LAN.

SMTP

• This protocol is dedicated for sending EMail messages over a TCP connection. SMTP defines a set of rules which allows two programs to send  and receive mail over the network. The protocol defines the data structure that would be delivered with information regarding the sender, the recipient (or several recipients) and, of course, the mail's body.

• SMTP lets us specify– Sender– Recipient– Message body

Demo SMTP

• We can telnet to the mail machine at princeton and send a message

• Don’t do this at home!!

Why should the internet not work

• Disorganized– Very heterogeneous– Large dose of anarchy– Grew quickly, continues to grow quickly

Why the internet works

• TCP/IP• Other protocols

– http– Smtp

• Lots of means of testing and seeing the network– Traceroute (on UNIX) (tracert on windows)– ping– www.arin.net (whois command)– www.caida.org (who sees who)

• http://www.caida.org/projects/internetatlas/gallery/ascore/demo.xml (step by step)

When things go wrong

• Code-red virus– On July 19, 2001 more than 359,000 computers were

infected with the Code-Red (CRv2) worm in less than 14 hours. At the peak of the infection frenzy, more than 2,000 new hosts were infected each minute. 43% of all infected hosts were in the United States, while 11% originated in Korea followed by 5% in China and 4% in Taiwan. The .NET Top Level Domain (TLD) accounted for 19% of all compromised machines, followed by .COM with 14% and .EDU with 2%. We also observed 136 (0.04%) .MIL and 213 (0.05%) .GOV hosts infected by the worm.

– Visualization

The Internet

• Where did it come from

• How has it grown

• Who owns the internet

Internet, as we know it

• 1960’s DoD built ARPANET– Experimental network

– Would function even in event of nuclear war

• 1985 NSF created NSFNET– Based on ARPRANET

– National backbone service

– Free to educational and research institutions

– Corporations (eg Sprint, MCI) built networks • Networks linked to NSFNET

Internet, as we know it (cont.)

• 1993 InterNIC created by NSF– directory and database services (AT&T)

– registration services (Network Solutions Inc.)

– information services (General Atomics/CERFnet)

• 1989 http created by Tim Berners-Lee – Released to high energy physicists in 1991

– Mosaic in 1993

– Netscape in 1994

Internet – key events

• 1961 Kleinrock – packet-switching theory

• 1966 Roberts – Plan for ARPANET

• 1969 – First ARPANET

With much help from Hobbes' Internet Timeline http://www.zakon.org/robert/internet/timelineCopyright (c)1993-2000 by Robert H Zakon.

First packets sent by Charley Kline at UCLA as he tried logging into SRI. The first attempt resulted in the system crashing as the letter G of LOGIN was entered. (October 29)

Internet – key events (cont.)

• 1973 – Ethernet invented– Email is 75% of ARPANET traffic

• 1974– TCP designed

• 1978– TCP split into TCP and IP

• 1980– First virus

Internet – key events (cont.)

• 1983– First nameserver– Cut over to TCP/IP

• 1984– DNS (Domain Name System) introduced

• .com, .edu, …

– Number of hosts above 1000

• 1988– CERT (Computer Emergency Response Team) formed

in response to Morris worm

Internet – key events (cont.)

• 1989– Number of hosts above 100,000

• 1990– ARPANET ceases to exist

• 1993– Mosaic; WWW proliferates at a 341,634% annual growth rate

of service traffic

• 1994– 25th anniversary of ARPANET

Growth in number of hosts

Growth in number of domains

Growth in number of networks

WWW Growth

Who owns the internet?

• Central organizations– InterNIC and its successors (for names)– ISP’s for transportation

• The networking community– Setting and following standards

• IETF (Internet Engineering Task Force)• W3C (World Wide Web Consortium)

– Network managers

Who owns the internet? (cont.)

• We all do– Information wants to be free– A lot of good social behavior is required

What happens next?

• Various scenarios…– Which one do you believe?

Networking (conclusion)

• At the bottom– Hardware generating packets– Protocols for packet transmission– Collision, backoff, …

• In the middle– TCP/IP is the key idea

• At the top– Some nice tools

• Ping, traceroute, … are useful

– Ports on my machine for http, ftp, fingerd, ping, …

A few questions

• What does it mean to be connected to the internet?– How is the web different from the internet?

• What about security?– Child security in chatroom– Would/should you give a credit card number

• What’s next?