internet an introduction. 2/3028.02.06 packet information sent in packets header...
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InternetInternet
An IntroductionAn Introduction
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PacketPacket
Information sent in packetsInformation sent in packets HeaderHeader
sender sender receiverreceivertype of servicetype of servicechecksumchecksum
BodyBodydatadata
size = 1500 - 65000 bytessize = 1500 - 65000 bytes
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IP layersIP layers
Physical layerPhysical layer unreliable connection between two computersunreliable connection between two computers
Link layerLink layer reliable connection between two computersreliable connection between two computers
IP layerIP layer reliable connection between two computers across the LANreliable connection between two computers across the LAN
TCP/UDP layerTCP/UDP layer ““virtual” connectionsvirtual” connections portsports
Application layerApplication layer HTTP, mail, ...HTTP, mail, ...
ISO/OSI Reference model – session and presentation layerISO/OSI Reference model – session and presentation layer
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Physical and link layerPhysical and link layer
Physical layerPhysical layer ensures data sending/receiving ensures data sending/receiving Ethernet, RS 232, WiFi, ATM, Novell, …Ethernet, RS 232, WiFi, ATM, Novell, …
Link layer - EthernetLink layer - Ethernet corrects errors of physical layercorrects errors of physical layer each net card has its own (unique) MAC each net card has its own (unique) MAC
(Machine Address Code) address(Machine Address Code) address 00-11-D8-C8-D6-6A00-11-D8-C8-D6-6A
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IP protocolIP protocol
sends data across heterogeneous sends data across heterogeneous networksnetworks
routerroutercontrols a subnet of the Internetcontrols a subnet of the Internet
source – target addresssource – target address IP address - 32-bit numberIP address - 32-bit number
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IP addressIP address
IP: IP: 10011110.11000011.10101010.10xxxxxx10011110.11000011.10101010.10xxxxxx 158.195.85.?158.195.85.?
mask:mask: 11111111.11111111.11111111.1100000011111111.11111111.11111111.11000000 255.255.255.192255.255.255.192
special addressesspecial addresses network = 158.195.85.128network = 158.195.85.128 broadcast = 158.195.85.191broadcast = 158.195.85.191
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ICMP and other IP protocolsICMP and other IP protocols
Internet Control Message ProtocolInternet Control Message Protocol pingping
echo requestecho request
echo replyecho reply destination unreachabledestination unreachable TTL exceededTTL exceeded
Other IP protocolsOther IP protocols IGMP, ARP, RARP, BOOTP, DHCP, TCP, IGMP, ARP, RARP, BOOTP, DHCP, TCP,
UDPUDP
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Static vs. dynamic IPStatic vs. dynamic IP
Static addressStatic address manual IP address, mask, DNS server settingmanual IP address, mask, DNS server setting
DHCP protocol (based on BOOTP)DHCP protocol (based on BOOTP) Dynamic Host Control ProtocolDynamic Host Control Protocol given a MAC address IP address of some IP given a MAC address IP address of some IP
address rangeaddress range also gives information about correct netmask also gives information about correct netmask
and DNS information for a particular LAN and DNS information for a particular LAN networknetwork
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TCP/UDPTCP/UDP
TCP (Transmission Control Protocol)TCP (Transmission Control Protocol) the most common connection-oriented the most common connection-oriented
protocol protocol most of Internet services use this protocol most of Internet services use this protocol
POP3, ...POP3, ...
UDP (User Datagram Protocol)UDP (User Datagram Protocol) no check, whether the data was received no check, whether the data was received
correctly correctly video, SMB, P2Pvideo, SMB, P2P
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PortPort
Every (virtual) connection between two Every (virtual) connection between two computer uses some portcomputer uses some port Well-known ports < 1024Well-known ports < 1024
used for some well-known services FTP, HTTP, used for some well-known services FTP, HTTP, SSH, ... SSH, ...
Dynamic ports > 1024Dynamic ports > 1024secondary communication and data transfersecondary communication and data transfer
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Packet examplePacket example
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Communication exampleCommunication examplePOP3 service = port 110POP3 service = port 110telnet sccg.sk 110telnet sccg.sk 110
Trying 158.195.85.131...Trying 158.195.85.131... Connected to sccg.sk (158.195.85.131).Connected to sccg.sk (158.195.85.131). Escape character is '^]'.Escape character is '^]'. +OK POP3 fractal.dam.fmph.uniba.sk 2004.89mdk server ready+OK POP3 fractal.dam.fmph.uniba.sk 2004.89mdk server ready
user kubiniuser kubini +OK User name accepted, password please+OK User name accepted, password please
pass tralalapass tralala +OK Mailbox open, 3 messages+OK Mailbox open, 3 messages
retr 2retr 2 +OK 386 octets +OK 386 octets Return-Path: Received: (from user.123@localhost) by pop.foo.bar (8.8.8/8.8.8) id Return-Path: Received: (from user.123@localhost) by pop.foo.bar (8.8.8/8.8.8) id
SAA29614 for user.123; Wed, 3 Dec 1997 18:55:43 -0500 (EST) Date: Wed, 3 SAA29614 for user.123; Wed, 3 Dec 1997 18:55:43 -0500 (EST) Date: Wed, 3 Dec 1997 18:55:43 -0500 (EST) From: Pat Gunn …Dec 1997 18:55:43 -0500 (EST) From: Pat Gunn …
dele 1dele 1 +OK Message 2 has been deleted.+OK Message 2 has been deleted.
quitquit+OK Sayonara+OK Sayonara
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SummarySummary
InternetInternet
PacketsPackets ICMP (Internet Control Message Protocol)ICMP (Internet Control Message Protocol) IP (Internet Protocol)IP (Internet Protocol) TCP/UDP (Transmission Control Protocol, TCP/UDP (Transmission Control Protocol,
User Datagram Protocol)User Datagram Protocol) PortsPorts Application specific informationApplication specific information
Server configurationServer configuration
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Linux basicsLinux basics
bash (shell)bash (shell)man bashman bashcd, cp, mv, rm, w, ps, …cd, cp, mv, rm, w, ps, …path path
absolute : /home/kubini/public_htmlabsolute : /home/kubini/public_html relative public_htmlrelative public_html
home directoryhome directoryprompt : kubini@fractal:~prompt : kubini@fractal:~mountmount
/proc/proc /dev/dev /etc/etc /mnt/mnt /bin, /sbin, /usr/bin, /usr/sbin/bin, /sbin, /usr/bin, /usr/sbin
user, group - chmod, chown, chgrpuser, group - chmod, chown, chgrp
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MAIL(SMTP, POP3)MAIL(SMTP, POP3)
mail sendingmail sending postfix = /etc/postfix/main.cf, /etc/init.d/postfix/restartpostfix = /etc/postfix/main.cf, /etc/init.d/postfix/restart
mail receivingmail receiving pop3(Post Office Protocol) = /etc/xinetd.d/pop3(s)pop3(Post Office Protocol) = /etc/xinetd.d/pop3(s)
unsecured protocolunsecured protocolmails are stored on the client (usually)mails are stored on the client (usually)
imap(Internet Mail Access Protocol) = imap(Internet Mail Access Protocol) = /etc/xinetd.d/imap(s)/etc/xinetd.d/imap(s)
newer safer protocolnewer safer protocolmails are stored on the servermails are stored on the server
/etc/init.d/xinetd restart/etc/init.d/xinetd restart
client = mail, pine, kmailclient = mail, pine, kmail
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DNSDNS
158.195.85.151 (ns.dam.fmph.uniba.sk)158.195.85.151 (ns.dam.fmph.uniba.sk)www.zoznam.skwww.zoznam.sk <-> 62.65.179.31 <-> 62.65.179.31MX, PTR, A, CNAMEMX, PTR, A, CNAMEhierarchical DNS name structurehierarchical DNS name structure .uniba.sk.uniba.sk .fmph.uniba.sk.fmph.uniba.sk .dai.fmph.uniba.sk.dai.fmph.uniba.sk
/etc/named.conf/etc/named.conf /var/named/…/var/named/… /etc/init.d/named restart/etc/init.d/named restart
client = dig, host – nslookup, ping -aclient = dig, host – nslookup, ping -a
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Webserver (httpd)Webserver (httpd)
Apache(Pyramid)Apache(Pyramid) server webpages (sccg.sk, …)server webpages (sccg.sk, …) user webpagesuser webpages
ConfigurationConfiguration vim /etc/httpd/conf/httpd2.conf, /etc/php.inivim /etc/httpd/conf/httpd2.conf, /etc/php.ini /etc/init.d/httpd restart/etc/init.d/httpd restart
Client = lynx, links, mozilla, IEClient = lynx, links, mozilla, IE
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DatabaseDatabase
MySQL server(fractal)MySQL server(fractal) port 3306port 3306 configurationconfiguration
vim /etc/my.cnfvim /etc/my.cnf
/etc/init.d/mysqld restart/etc/init.d/mysqld restart relational databaserelational database SQL (Structured Query Language)SQL (Structured Query Language)
ClientClienthttp://http://www.sccg.sk/phpMyAdminwww.sccg.sk/phpMyAdmin
mysql –u user –p passmysql –u user –p pass
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SMB(Server Message Block)SMB(Server Message Block)
Samba serverSamba server ports: TCP 139, 440, UDP 137, 138, …ports: TCP 139, 440, UDP 137, 138, … /etc/samba/smb.conf/etc/samba/smb.conf
WorkGroup(KG, KPGSO) = browstatWorkGroup(KG, KPGSO) = browstat
Domain (M-115)Domain (M-115)
Client: smbmount, smbclient, smbumount, Client: smbmount, smbclient, smbumount, explorer(explorer(\\fractal\pub\\fractal\pub), Windows shared disks), Windows shared disks net use Q: net use Q: \\fractal\pub\\fractal\pub /user:Administrator /user:Administrator print$, ipc$, … print$, ipc$, …
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FTP(File Transfer Protocol)FTP(File Transfer Protocol)
Server (not running)Server (not running) proftpdproftpd
/etc/proftpd.conf/etc/proftpd.conf
/etc/init.d/proftpd restart/etc/init.d/proftpd restart anonymous ftpanonymous ftp
ClientClient ftp, mc, explorer (ftp://...), Total Commanderftp, mc, explorer (ftp://...), Total Commander passive vs. active ftppassive vs. active ftp
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TelnetTelnet
Server (not running7)Server (not running7) Port 23Port 23 „„remote keyboard“remote keyboard“
ClientClient telnet (Linux and Windows)telnet (Linux and Windows)
Ctrl+] – if the connection gets broken Ctrl+] – if the connection gets broken
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SSH(Secure shell)SSH(Secure shell)
Secure shell serverSecure shell server Safe telnet replacementSafe telnet replacement /etc/ssh/sshd.conf/etc/ssh/sshd.conf /etc/init.d/sshd restart/etc/init.d/sshd restart
ClientClient SecureCRT, putty, ssh(Secure Shell)SecureCRT, putty, ssh(Secure Shell) scp(sftp), WinScp(Secure coPy – ftp scp(sftp), WinScp(Secure coPy – ftp
replacement) replacement)
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Firewall/RouterFirewall/Router
router:router: computer “responsible” for a subnetcomputer “responsible” for a subnet routes packets to/from the correct computersroutes packets to/from the correct computers
firewall:firewall: ensures safety of the subnetensures safety of the subnet iptables iptables firewall(off|on)firewall(off|on)
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Spam filterSpam filter
SpamAssassinSpamAssassin /etc/mail/spamassassin/local.cf/etc/mail/spamassassin/local.cf spam, whitelist, blacklist, ...spam, whitelist, blacklist, ...
Client configurationClient configuration ~/.spamassassin/local.cf~/.spamassassin/local.cf
similar to server configurationsimilar to server configuration
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Proxy serverProxy server
Proxy serverProxy server content based filteringcontent based filtering
fromfromtototype of servicetype of service
SQUID – application proxySQUID – application proxyapplication layer content filteringapplication layer content filteringM-115 has restricted access to KPGSO LANM-115 has restricted access to KPGSO LAN/etc/squid.conf/etc/squid.conf/etc/init.d/squid restart/etc/init.d/squid restart
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X-WindowsX-Windows
ServerServer X-Window X-Window
physical console Alt-F7physical console Alt-F7
local server = WinAxelocal server = WinAxe
ClientClient applicationsapplications
xterm, ...xterm, ...
kclock, kmailkclock, kmail
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DHCPDHCP
ServerServer dhcpddhcpd /etc/init.d/dhcpd restart/etc/init.d/dhcpd restart /etc/dhcpd/dhcpd.conf/etc/dhcpd/dhcpd.conf
dynamically assign IP address from some rangedynamically assign IP address from some rangeMAC filteringMAC filtering DHCP assigns IP address to computers with known DHCP assigns IP address to computers with known
MAC addressMAC address
ClientClient ipconfig /renew, …ipconfig /renew, …
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Our LANOur LAN
Experiment (M-113, 158.195.85.147)
KPGSO LAN
Pracovné stanice
Fakultna LANFractal (M-123, 158.195.85.131)
MAIL (POP3, IMAP, SMTP)MYSQL
SSH, SCP, SFTP
Pyramid (M-123, 158.195.85.159)HTTP [php](WebMail
phpMyAdminWebStranky)
Ns(M-123, 158.195.85.151)DNS
M115-Proxy,M-115 NT Domain Controller
Torus, Tebe (158.195.85.129)Firewall
M115 - LAN
Scanner
Minolta (M-113, 158.195.85.154)HTTP
Canon (M-119)
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ReferencesReferences
www.sccg.sk/~kubini/Internetwww.sccg.sk/~kubini/Internet
InternetInternet IBM TCP/IP referenceIBM TCP/IP reference RFC (Request for comments)RFC (Request for comments) GoogleGoogle
LinuxLinux manman standard documentation and Internet (google)standard documentation and Internet (google)
Interesting softwareInteresting software Ethereal (packet analyzer)Ethereal (packet analyzer)