Jozef Goetz, expanded by Jozef Goetz, 2009 Credits: Parts of the slides are based on slides created by UNIX textbook authors, Syed M. Sarwar, Robert Koretsky, Syed A. Sarwar, 2005 Addison Wesley

Jozef Goetz, Objectives You may ignore slides from 66 to the end. To describe networks, the Internet and internetworks and explain why they are used To discuss briefly the TCP/IP protocol suite, IP addresses, protocol ports, and internet services and applications To explain what the client-server software model is and how it works To discuss various network software tools for electronic communication, 1. remote login, 2. file transfer, 3. remote command execution, and 4. status reporting To describe briefly the secure shell To cover the commands and primitives

Jozef Goetz, Computer Networks and Internet works When two or more computer hardware resources are connected they form a computer network 1. Local area Networks (LANs) 2. Metropolitan area networks (MANs) 3. Wide area networks (WANs) An internetwork is a network of networks

Jozef Goetz, A brief history of the Internet ARPANET (50s and 60s, some universities) NSFNET (late 70s, all universities) TCP/IP (invention ’74) became the official protocol in When NSFNET and the ARPANET were connected, the growth became exponential Many regional networks (Canada, Europe, the Pacific) joined up In mid-80s people began viewing the collection of networks as the Internet The glue that holds the Internet together is the TCP/IP reference model and TCP/IP protocol stack ANS (Advanced Networks and Service) by MERIT, MCI, and IBM took over NSFNET in 1990 as ANSNET ANSNET sold to American Online in 1995.

Jozef Goetz, The ARPANET The original ARPANET design. IMP - Interface Message Processor

Jozef Goetz, The ARPANET Growth of the ARPANET (a) December (b) July (c) March (d) April (e) September 1972.

Jozef Goetz, NSFNET The NSFNET backbone in 1988.

Jozef Goetz, Internet Usage Machine is on the Internet if it runs the TCP/IP protocol stack, has an IP address, and can send IP packets to all the other machines on the Internet Millions PC can call up an Internet service provider using a modem, be assigned a temporary (dynamic) IP address, and send IP packets to all the other hosts The ch-r of the network was changed from an academic and military playground to a public utility

Jozef Goetz, Internet Usage Traditional applications (1970 – 1990) News newsgroups devoted to different topics) Remote login Using telnet, WinSCP, rlogin, ssh programs File transfer Using FTP programs

Jozef Goetz, What is the World Wide Web? From the Free Online Dictionary of Computing:Free Online Dictionary of Computing "An Internet client-server hypertext distributed information retrieval system. " The Web is not a network. The Web is not the Internet itself. The Web is not a proprietary system like AOL. Instead the Web is a system of clients (Web browsers) and servers that uses the Internet for its data exchange. Web is a system of clients (Web browsers) and servers that uses the Internet for its data exchange On the WWW everything (documents, menus, indices) is represented to the user as a hypertext object in HTML format. Hypertext links refer to other documents by their URLs. hypertextHTMLHypertext linksURLs These can refer to local or remote resources accessible via FTP, Gopher, Telnet or news, as well as those available via the http protocol used to transfer hypertext documents.FTP GopherTelnetnewshttphypertext

Jozef Goetz, History of the Internet and World Wide Web WWW Allows computer users to locate and view multimedia-based documents Introduced in 1991 by Tim Berners-Lee Developed information system based on hyperlinked text documents HyperText Markup Language (HTML) Developed communication protocols as backbone WWW today Makes info instantly accessible Merges computing and communication technologies

Jozef Goetz, Internet Usage In ’91 Tim Berners-Lee at CERN (Switzerland) invented the WWW (World Wide Web) to a hyperlink (HTTP) access to documents brought millions of nonacademic users In ’93 development of Mosaic by Marc Anderson, the first graphics-based web browser at NCSA This created an interface to the Web that was easy to use – just point and click instead of remembering text commands This set the stage for easier information sharing and retrieval

Jozef Goetz, Architecture of the Internet. Overview of the Internet. Signal is transferred to the ISP’s (Internet Service Provider) POP – Point of Present (located in the tel. switching office) and injected into the ISP’s regional network from this point the system is fully digital and packet switched A NAP (Network Access Point) is a room full of routers, at least one per backbone A LAN in the room connects all the routers, so packets can be forwarded from any backbone to any other backbone

Jozef Goetz, Collection of Subnetworks The Internet is an interconnected collection of many networks. SNA: Systems Network Architecture - IBM's mainframe network standards

Jozef Goetz, X.25 Networks Developed during 70's. 1st public data network interface between public packet-switched networks and customers. Data packet has a 3-byte header a 12 bit connection #, a packet sequence #, an acknowledgment # etc. and up to 126 bytes of data Operate at 64 Kbps, so are very slow and becoming outdated. However there are still many of them in operation. Connection oriented: Uses: Switched Virtual Circuit established when the first packet is sent circuit remains for duration of session providing in-order delivery, and flow control. Permanent Virtual Circuit established by agreement between the customer and the carrier: Like a leased line

Jozef Goetz, Frame Relay Takes advantage of modern high-speed reliable digital phone lines. Connection oriented. Property: In-order delivery, no error control, no flow control, akin to LAN This allows simple protocols with work done by user computers rather than by the network. Runs at 1.5 Mbps with few features. Customer leases a permanent virtual circuit between two points. this "virtual leased line" means that the wire is shared with other users at a great price reduction.

Jozef Goetz, Broadband ISDN and ATM Connection oriented. ISDN (Integrated Services Digital Network) offers cable, video on demand, , etc. ATM (Asynchronous Transfer Mode) early ’90s is underlying Mechanism inside the tel. system. Transmits in small fixed-size cells. Not synchronous. Was supposed to merge voice, data, cable TV, telex, telegraph etc. into a single integrated system – it didn’t happen Alive, used by carriers for internal transport

Jozef Goetz, (a) Computer Networks and (b) Internetworks R – router H - host

Jozef Goetz, Why Computer Networks and Internetworks? Sharing of computer resources computers, printers, plotters, scanners, files and software Network as a communication medium inexpensive, fast, reliable Cost efficiency large computing power available Less performance degradation if one computer crashes, the remaining ones are still up

Jozef Goetz, Network Models International Standards Organization’s Open System Interconnect Reference Model (ISO’s OSI 7-Layer Reference Model) The TCP/IP 5-layer Model Used in the Internet

Jozef Goetz, Network Models with approximate mapping between the two The first 4 layers deal with the communication between hosts. The 5 th layer deals with the Internet services provided by various applications. Most of the 1 st layer is handled by hardware (communication medium used, attachments of hosts to the medium). The rest of the 1st layer and all the 2 nd layer is handled by the (Network Interface Card) NIC card in a host. Layers 3 and 4 are fully implemented in the operating systems kernel on most existing systems. The first 2 layers are network hardware specific, the others are work independently of the physical layer

Jozef Goetz, Reference Models Protocols and networks in the TCP/IP model initially. The Application layer contains all of the higher- level protocols – telnet - virtual terminal protocol – FTP – file transfer – SMTP – – DNS - Domain Name System – NNTP - Network News Transfer Protocol – HTTP - Hypertext Transfer Protocol

Jozef Goetz, The TCP/IP Protocol Suite As a user you can see the application layer from applications and utilities: 1. Web browsing, 2. file transfer, 3. remote login 4. etc. 1 st -2 nd layer is handled by the Network Interface Card -NIC card

Jozef Goetz, The TCP/IP Protocol Suite IGMP - Internet Group Management Protocol handles multicasting ICMP - Internet Control Message Protocol Handles errors and control messages. Protocol is used to forward information, primarily error messages. To see if a computer is running, the `ping' program sends an echo request, which is part of ICMP. ARP -Address Resolution Protocol is a protocol for mapping an Internet Protocol IP address to a physical machine address that is recognized in the local network. For example, in IP Version 4, the most common level of IP in use today, an address is 32 bits long. In an Ethernet LAN, however, addresses for attached devices are 48 bits 1 st -2 nd layer is handled by the Network Interface Card -NIC card RARP - Reverse Address Resolution Protocol is a protocol by which a physical machine in a LAN can request to learn its IP address from a gateway server's Address Resolution Protocol (ARP) table or cache. A network administrator creates a table in a LAN’s gateway router that maps the physical machine (addresses) into IP addresses.

Jozef Goetz, Transport Layer: The TCP and UDP The purpose of the transport layer is to transport application data from your machine to a remote machine and vice versa User Datagram Protocol (UDP) is a connectionless protocol, offers the best effort delivery service Transmission Control Protocol (TCP) is a connection-oriented protocol that establish a virtual connection with the destination before transmitting data, thus the TCP leads completely reliable, error free in-sequence delivery of data

Jozef Goetz, Routing of the Application Data The Internet Protocol (IP) The network layer is responsible for routing application data to the destination host IP is responsible for transporting IP datagrams containing TCP segments or UDP datagrams to the destination host The IP is a connectionless protocol, it simply sends the application data without establishing virtual connection with the destination before transmitting data, thus the IP routing is best effort and doesn’t guarantee delivery of TCP segments or UDP datagrams

Jozef Goetz, Routing of the Application Data The Internet Protocol (IP) In IPv4 the IP address (32 bits) is divided into three fields: 1. address class, 2. network ID and 3. host ID The address class field identifies the class of the address and dictates the number of bits used in the network ID and host ID fields This scheme has 5 address classes : A,B,C,D,E

Jozef Goetz, IPv4 Addresses in Dotted Decimal Notation 32-bit binary numbers are difficult to remember IPv4 addresses are given in dotted decimal notation (DDN) In DDN all 4 bytes of an IPv4 address are written in their decimal equivalents and are separated by dots Example:

Jozef Goetz, IP Addresses IP address formats (or 127.x.x.x, where x is between 0-127) is known as localhost is used to send a data packet to itself. for testing purpose. host ID = 1…1 is the broadcast address in order to send a data packet to all hosts on a network

Jozef Goetz, IPv4 Address Classes The sum of network IDs for class A, B, C = 2^7 + 2^14 + 2^21 = 1,113,664 networks The sum of hosts IDs for class A, B, C = 2^24 + 2^16 + 2^ 8 = 3,758,096,400 hosts

Jozef Goetz, IPv4 Address Classes Prove all ranges!!!

Jozef Goetz, IPv4 Address Classes A: Very large organizations and government agencies B: Large organizations: AT&T, IBM, MIT, large universities etc. C: Small to medium sized organizations: ISP, small consulting companies, community colleges, universities In IPv4 the IP address (32 bits) In IPv6 the IP address is 128 bits and it covers the # of hosts 6 x 2^28 times the present world population

Jozef Goetz, IPv4 Address Classes Figure 14.5 An internetwork of 4 networks with one class A, one class B, and 2 class C networks connected via 4 routers class A class C class B

Jozef Goetz, Symbolic Names Symbolic names are easier to remember remain the same even if the numeric address changes must be unique for a host on the Internet Format: hostname.domain_name e.g. students.up.edu where: domain_name = organization_name.top-level_domain organization_name is assigned by the Network Information Center e.g. ulv.edu Attaching the name of a host to a domain name with a period between them yields the fully qualified domain name (FQDN) for the host e.g. egr.up.edu – egr is a host name at the University of Portland

Jozef Goetz, A portion of the Internet domain name hierarchy

Jozef Goetz, Top-Level Internet Domains

Jozef Goetz,

Jozef Goetz, The Domain Name System Domain Name System (DNS) service translates symbolic names to equivalent IP addresses DNS implements a distributed database of name-to-address mappings A set of dedicated hosts run name servers that take requests from the application software and work together to map domain names to the corresponding IP addresses every organization runs at least 1 domain name server app uses gethostbyname() to get its IP address

Jozef Goetz, Inverse domain The servers that handle the inverse domain are also hierarchical. This means the netid part of the address should be at a higher level than the subnetid part, and the subnetid part higher than the hosted part. In this way, a server serving the whole site is at a higher level than the servers serving each subnet. To follow the convention of reading the domain labels from the bottom to the top, an IP address such as (a class 13: address with netid ) is read as in-addr. area. This configuration makes the domain look inverted when compared to a generic or country domain.

Jozef Goetz, DNS lookup utility: host [jgoetz jgoetz]$ host ulv.edu ulv.edu has address ulv.edu mail is handled (pri=5) by mxg1.ulv.edu ulv.edu mail is handled (pri=5) by mxg2.ulv.edu [jgoetz jgoetz]$ host IN-ADDR.ARPA domain name pointer cs253u]$ host ecs.fullerton.edu ecs.fullerton.edu has address cs253u]$ host in-addr.arpa domain name pointer ecs.fullerton.edu. cs253u]$

Jozef Goetz, The Domain Name System #DNS service is to use a static host file /etc/hosts #a static hosts file contains the domain names and their IP addresses configured by the system admin $ cat /etc/hosts [jgoetz jgoetz]$ cat /etc/hosts localhost raq4.ulv.edu # Cobalt automated entry for eth loki.ulv.edu loki #Veritas Backup Server #to view IP address and other info about host’s interface to the network $ /sbin/ifconfig –a # faculty.ulv.edu has [jgoetz jgoetz]$ /sbin/ifconfig -a eth0 Link encap:Ethernet HWaddr 00:10:E0:05:A8:F4 inet addr: Bcast: Mask: UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets: errors:0 dropped:0 overruns:0 frame:0 TX packets: errors:3 dropped:0 overruns:0 carrier:3 collisions:0 txqueuelen:100 Interrupt:5 Base address:0x8000 eth1 Link encap:Ethernet HWaddr 00:10:E0:05:A8:F3 BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:100 Interrupt:9 Base address:0x8100 lo Link encap:Local Loopback inet addr: Mask: UP LOOPBACK RUNNING MTU:3924 Metric:1 RX packets: errors:0 dropped:0 overruns:0 frame:0 TX packets: errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0$

Jozef Goetz, The Domain Name System cs253u]$ cat /etc/hosts # Do not remove the following line, or various programs # that require network functionality will fail localhost.localdomain localhost shell ldap.int.ecs.fullerton.edu ldap ecsmysql.ecs.fullerton.edu ecsmysql mail.ecs.fullerton.edu mail lupus.ecs.fullerton.edu lupus lupus2.ecs.fullerton.edu lupus2

Jozef Goetz, The Domain Name System #lookup for the IP address of a host name: cs253u]$ nslookup ecs.fullerton.edu Server: # name server Address: #53 Name: ecs.fullerton.edu Address: [jgoetz jgoetz]$ nslookup ulv.edu Server: ns.ulv.edu Address: Name: ulv.edu Address: ~]$ nslookup faculty.ulv.edu Server: ns.ulv.edu # this a name server Address: Name: faculty.ulv.edu Address: #nslookup uses file /etc/resolv.conf to find the host that runs the name server and passes the request over it. ~]$ host IN-ADDR.ARPA domain name pointer FACULTY.ULV.EDU

Jozef Goetz, The Domain Name System nslookup uses file /etc/resolv.conf to find the host that runs the name server and passes the request over it. cs253u]$ cat /etc/resolv.conf nameserver nameserver DNS lookup utility: dig interacts with name servers specified in /etc/resolv.conf and display their responses – gives more info than nslookup

Jozef Goetz, The Domain Name System ~]$ dig faculty.ulv.edu ; > DiG 8.3 > faculty.ulv.edu ;; res options: init recurs defnam dnsrch ;; got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 2 ;; QUERY SECTION: ;; faculty.ulv.edu, type = A, class = IN ;; ANSWER SECTION: faculty.ulv.edu. 1D IN A ;; AUTHORITY SECTION: ulv.edu. 1D IN NS ns.ulv.edu. ulv.edu. 1D IN NS ns2.ulv.edu. ;; ADDITIONAL SECTION: ns.ulv.edu. 1D IN A ns2.ulv.edu. 1D IN A ;; Total query time: 25 msec ;; FROM: raq4.ulv.edu to SERVER: default ;; WHEN: Wed Nov 16 22:25: ;; MSG SIZE sent: 33 rcvd: 116 [jgoetz jgoetz]$ dig ulv.edu ; > DiG 8.3 > ulv.edu ;; res options: init recurs defnam dnsrch ;; got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 2 ;; QUERY SECTION: ;; ulv.edu, type = A, class = IN ;; ANSWER SECTION: ulv.edu. 12H IN A ;; AUTHORITY SECTION: ulv.edu. 12H IN NS ns2.ulv.edu. ulv.edu. 12H IN NS ns.ulv.edu. ;; ADDITIONAL SECTION: ns.ulv.edu. 12H IN A ns2.ulv.edu. 12H IN A ;; Total query time: 11 msec ;; FROM: raq4.ulv.edu to SERVER: default ;; WHEN: Thu Nov 15 16:21: ;; MSG SIZE sent: 25 rcvd: 108

Jozef Goetz, The Domain Name System [jgoetz jgoetz]$ dig ulv.edu ; > DiG 8.3 > ulv.edu ;; res options: init recurs defnam dnsrch ;; got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 2 ;; QUERY SECTION: ;; ulv.edu, type = A, class = IN ;; ANSWER SECTION: ulv.edu. 12H IN A ;; AUTHORITY SECTION: ulv.edu. 12H IN NS ns2.ulv.edu. ulv.edu. 12H IN NS ns.ulv.edu. ;; ADDITIONAL SECTION: ns.ulv.edu. 12H IN A ns2.ulv.edu. 12H IN A ;; Total query time: 11 msec ;; FROM: raq4.ulv.edu to SERVER: default ;; WHEN: Thu Nov 15 16:21: ;; MSG SIZE sent: 25 rcvd: 108 dig ecs.fullerton.edu ; > DiG > ecs.fullerton.edu ;; global options: printcmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 0 ;; QUESTION SECTION: ;ecs.fullerton.edu. IN A ;; ANSWER SECTION: ecs.fullerton.edu IN A ;; AUTHORITY SECTION: ecs.fullerton.edu IN NS ecs.fullerton.edu. ;; Query time: 22 msec ;; SERVER: #53( ) ;; WHEN: Fri Mar 14 23:54: ;; MSG SIZE rcvd: 65

Jozef Goetz, Well-known Internet Services

Jozef Goetz, The Client-Server Software Model Internet services are implemented by using a paradigm in which the software for a service is partitioned into 2 parts The part that runs on the host on which the user running the application is logged on to is called the client software The part that’s usually starts running when a host boots is called the server software Connection-oriented client server models: client sends a connection request to the server and the server either rejects or accepts the request. If server accepts the request, the client and server are said to be connected through a virtual connection

Jozef Goetz, The Client-Server Software Model

Jozef Goetz, Displaying the Names. uname [OPTION]... DESCRIPTION Print certain system information. With no OPTION, same as -s. -a, --all print all information -m, --machine print the machine (hardware) type -n, --nodename print the machine's network node hostname -r, --release print the operating system release -s, --sysname print the operating system name -p, --processor print the host processor type -v print the operating system version --help display this help and exit --version output version information and exit [jgoetz jgoetz]$ uname Linux [jgoetz jgoetz]$ uname -n raq4.ulv.edu [jgoetz jgoetz]$ uname -a [jgoetz jgoetzLinux raq4.ulv.edu C37_V #1 Sat Apr 12 15:06:43 PDT 2003 i686 unknown

Jozef Goetz, Displaying the Host Name $ uname -n yamsrv1.ece.gatech.edu $ uname -a SunOS yamsrv1.ece.gatech.edu 5.8 Generic_ sun4u sparc SUNW,Ultra-250 cs253u]$ whatis hostname hostname (1) - show or set the system's host name $ hostname – name of the host you are logged on to yamsrv1.ece.gatech.edu [jgoetz jgoetz]$ hostname raq4.ulv.edu -a, --all print all information -m, --machine print the machine (hardware) type -n, --nodename print the machine's network node hostname --help

Jozef Goetz, cpu info. cs253u]$ less /proc/cpuinfo processor : 1 vendor_id : AuthenticAMD cpu family : 15 model : 35 model name : Dual Core AMD Opteron(tm) Processor 175 stepping : 2 cpu MHz : cache size : 1024 KB fdiv_bug : no hlt_bug : no f00f_bug : no coma_bug : no fpu : yes fpu_exception : yes cpuid level : 1 flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext lm 3dnowext 3dnow lahf_ lm pni /proc/cpuinfo (END)

Jozef Goetz, Remote Login. The telnet protocol is designed to allow you to connect to a remote computer over a network telnet [options] [host[port]] Purpose:To connect to a remote system ‘host’ via a network; the ‘host’ can be specified by its name or IP address in dotted decimal notation Commonly used options/features: -a Attempt automatic login -l Specify a user for login usage: telnet [-l user] [-a] host-name [port] e.g. titan/bin > telnet -l jgoetz -a faculty.ulv.edu Trying Connected to FACULTY.ULV.EDU ( ). Escape character is '^]'. Password: Last login: Wed Nov 29 13:00:01 from cpe … telnet help //or telnet --help // to get available cmds

Jozef Goetz, Remote Login (contd.) [jgoetz jgoetz]$ telnet -? telnet: invalid option -- ? Usage: telnet [-8] [-E] [-L] [-S tos] [-a] [-c] [-d] [-e char] [-l user][-n tracefile] [-b hostalias ][-r] [host-name [port]] Ctrl + D close the session

Jozef Goetz, Remote Login (contd.) # reverts to the telnet client – place in the foreground

Jozef Goetz, Using Telnet to Invoke Other Well-known Services invokes a daytime service running at port 13

Jozef Goetz, Remote Login (contd.) [ cs253u]$ telnet -l cs253u -a ecs.fullerton.edu Trying Connected to ecs.fullerton.edu ( ). Escape character is '^]'. Password: Linux CentOS * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *** Welcome To Titan *** *** California State University at Fullerton *** *** Department of Computer Science *** ================================================================== This system follows rules and policy set down by the Computer Science Department. By using this system you expressly consent to all rules and policies which govern this system. Visit for tutorials, downloads and additional information about the system. ================================================================== You have mail. $ telnet upsun29 Trying Connected to upsun29.egr.up.edu. Escape character is ‘^]’. UNIX(r) System V Release 4.0 (upsun29.egr.up.edu) login: sarwar Password: ********** Last login: Sat Dec 27 05:05:37 from up You have mail. DISPLAY = (‘) TERM = (vt100) $

Jozef Goetz, File Transfer ftp [options] [host] Purpose: To transfer files from or to a remote ‘host’ Commonly used options/features -d Enable debugging -i Disable prompting during transfers of multiple files -v Show all remote responses

Jozef Goetz, File Transfer titan/jozefg > ftp -v faculty.ulv.edu // -v Show all remote responses Connected to faculty.ulv.edu. 220 ProFTPD Server (ProFTPD) [ ] 500 AUTH not understood KERBEROS_V4 rejected as an authentication type Name (faculty.ulv.edu:jozefg): jgoetz 331 Password required for jgoetz. Password: 230 User jgoetz logged in. Remote system type is UNIX. Using binary mode to transfer files. ftp> ls -l 200 PORT command successful 150 Opening ASCII mode data connection for file list -rw-r--r-- 1 jgoetz site Nov 28 21:01 Assig.doc -rwxrwxrwx 1 jgoetz site7 13 Oct 31 07:22 m drwxrwsr-x 4 jgoetz site Jun web 226 Transfer complete. ftp>

Jozef Goetz, File Transfer

Jozef Goetz,

Jozef Goetz, Testing a Network Connection ping [options] hostname Purpose:Send an IP datagram to ‘hostname’ to test whether it is on the network (or Internet); if the host is alive it simply echoes the received datagram Output:Message(s) indicating whether the machine is alive Commonly used options/features: -c count Send and receive ‘count’ (e.g. 3) packets -f Send 100 packets per second or as many as can be handled by the network; only the superuser can use this option -s packetsize Send ‘packetsize’ packets; the default is 56 bytes (plus an 8 byte header)

Jozef Goetz, Testing a Network Connection ping -c count Send and receive ‘count’ packets ping -s packetsizeSend ‘packetsize’ packets; the default is 56 bytes (plus an 8 byte header); Test yahoo.com

Jozef Goetz, Copyright © 2005 Pearson Addison- Wesley. All rights reserved. Utility Commands Examining System Setups whereis, whoami $ whoami bobk $ whereis mkdir mkdir: /usr/bin/mkdir $ Printing and General Utility Commands lpr, cal $ lpr -Pprintname file_name $ lpr –Pcs200 file_name // print your file in CS200 at the printer designated // as cs200 - you can find this format by entering // $help => look for “printing” $ cal // display calendar $ cal Communication Commands $ who // check the user name to whom you want to talk $ mesg [y|n] // permit execution write or talk $ write username $ biff [y|n] // notification on/off

Jozef Goetz, Copyright © 2005 Pearson Addison- Wesley. All rights reserved. Utility Commands (Contd) 

Jozef Goetz, Displaying Users on a Network $ rwho | more - remote who displays info about the user currently using machines on your network: log name, computer:terminal, date and time the user logged in Bobkupibm7:ttyC4 Jul 26 12:03 Dfrakesupibm47:ttyp2 Jul 26 11:49 Lulayupsun17:pts/0 Jul 26 10:17 Osterupsun17:pts/2 Jul 26 12:28 Sarwarupibm7:ttyp2 Jul 26 11:15 $ rwho -a | more Bobkupibm7:ttyC4 Jul 26 12:03 dfrakes upibm47:ttyp2 Jul 26 11:49 kent upibm48:ttyp0 Jul 26 03:41 8:49 kittyt upibm9:ttyp0 Jul 26 07:36 1:28 kuhn upsun29:console Jul 16 13:11 99:59 lulay upsun17:pts/0 Jul 26 10:17 oster upsun17:pts/2 Jul 26 12:28 pioster upsun20:pts/0 Jul 26 09:53 2:41 sarwar upibm7:ttyp2 Jul 26 11:15 sarwar upsun29:pts/0 Jul 26 11:24 1:00 $

Jozef Goetz, Displaying Users on a Network. rusers [options] [host_list] Purpose:Display the login names of the remote users logged on to all the machines on our local network Output:Information about the users logged on to the hosts on your local network in one line per machine format Commonly used options/features: -a Display all host names even if no user is using it -l Display the user information in a long format similar to that displayed by the who command

Jozef Goetz, Displaying Users on a Network for particular machine

Jozef Goetz, Displaying the Status of Hosts on a Network ruptime [options] – remote uptime Purpose:Show status of all connected machines on the local area network Output:Status of machines including machine name, up/down status, time a machine has been up (or down) for-called machine uptime, and the number of users logged on to the machine Commonly used options/features after sorting : -l Display output after sorting it with load average -t Display output after sorting it by machine uptime -u Display output after sorting it by the number ofusers

Jozef Goetz, Displaying the Status of Hosts on a Network Commonly used options/features after sorting : -l Display output after sorting it with load average -t Display output after sorting it by machine uptime -u Display output after sorting it by the number ofusers

Jozef Goetz, Displaying Information About Users finger [options] [user_list] Purpose:Display information about the users in the ‘user_list’; without a ‘user_list’, the command displays a short status report about all the users currently logged on to the specified hosts Output:User info extracted from the ~/.project and ~/.plan files Commonly used options/features: -m Match ‘user_list’ to login names only -s Display output in a short format cs253u]$ finger cs253u2 Login: cs253u2 Name: User Directory: /home/titan0/class/cs253u/cs253u2 Shell: /bin/bash Never logged in. No mail. No Plan.

Jozef Goetz, Displaying Information About Users ~]$ finger -s Jozef Login Name Tty Idle Login Time Office Office Phone jgoetz Jozef Goetz pts/1 Nov 30 21:05 ( ) ~]$ ~]$ finger -m jgoetz Login: jgoetz Name: Jozef Goetz Directory: /home/sites/site7/users/jgoetz Shell: /bin/bash On since Wed Nov 30 21:05 (PST) on pts/1 from No mail. No Plan. -m Match ‘user_list’ to login names only -sDisplay output in a short format

Jozef Goetz, Displaying Information About Users -m Match ‘user_list’ to login names only -sDisplay output in a short format

Jozef Goetz, Displaying Information About Users // if the finger server is running [jgoetz jgoetz]$ finger [ulv.edu] finger: connect: No route to host [jgoetz jgoetz]$

Jozef Goetz, The rlogin Command The rlogin command allows you to log on to a host on your local network (or remote) rlogin [options] hosts Purpose:To connect to a remote LINUX or UNIX ‘host’ via a network ; the ‘host’ can be specified by its name or IP address in the dotted decimal notation Commonly used options/features: -ec Set the escape character to ‘c’( the default is ‘~’) -l user User ‘user’ as the login name on the remote host slogin [options] hosts - secure version uses strong cryptography for transmitting data e.g. [jgoetz jgoetz]$ rlogin -l jozefg ecs.fullerton.edu ecs.fullerton.edu: Connection refused // it is not a local network

Jozef Goetz, The rlogin Command $ rlogin upsun -l perform Password: Last login: Mon Dec 18 12:08:12 from upsun21.up.edu SunOS Release (UPSUN_SERVER) #5: Mon Nov 14 17:31:44 PST 1994 DISPLAY 5 (upx46:0.0) TERM 5 (vt100) $ whoami perform $ hostname upsun.egr.up.edu $ -ec Set the escape character to ‘c’( the default is ‘~’) -l userUser ‘user’ as the login name on the remote host

Jozef Goetz, Remote Command Execution rsh – remote shell rsh [options] host [command] Purpose: To execute a command on a remote machine, ‘host’, on the same network; the rlogin command is executed if no ‘command’ is specified Commonly used options/features: -l user Use ‘user’ as the login name on the remote host ssh [options] host [command] -secure version uses strong cryptography for transmitting data

Jozef Goetz, Figure 14.8 The semantics of the rsh upsun29 ps command The same network

Jozef Goetz, Figure 14.9 The semantics of the rsh upsun29 sort students > sorted_students command students and sorted_students are files

Jozef Goetz, Remote Command Execution

Jozef Goetz, Remote Command Execution input from local file students and store the sorted result in a sorted_students file on the remote machine the sort cmd takes input from the students file on the local machine, (upibm7) and the output is sent to the sorted_students file on the local machine When used without arguments, the rsh reverts to the rlogin command. it is executed if no ‘arguments’ is specified //to log on a different network on the Internet

Jozef Goetz, Remote Copy rcp[options] [host:]sfile [host:]dfile rcp[options] [host:]sfile [host:]dir Purpose: To copy ‘sfile’ to ‘dfile’ source file – sfile destination file - dfile Commonly used options/features -p Attempt to preserve file modify and access times; without this option the command uses the current value of unmask to create file permissions -r Recursively copy files at ‘sfiles’ to ‘dir’

Jozef Goetz, Remote Copy (contd.) $ rcp ~/myweb/*.html upsun29:webmirror $ rcp ~/unixbook/Chapter[1-9].doc upsun29:unixbook.backup $ rcp upsun29:ece446/projects/*.[c,C] ~/swprojects.backup $ rcp -rp www1:* www2: $ Secure version of the rcp command $ scp prog4.c upsun29:~/courses/cs213/programs/ $ scp -r upsun21.egr.up.edu:courses. $ scp -rp www1:* www2: $ -p Attempt to preserve file modify and access times; -r Recursively copy files at ‘sfiles’ to ‘dir’

Jozef Goetz, Interactive Chat talk user [tty] Purpose:to initiate interactive chat with ‘use’ who is logged in on a ‘tty’ terminal $ talk bob [Waiting for your party to respond] Message from at 13:36... talk: connection requested by talk: respond with: talk $ talk

Jozef Goetz, Tracing the Route from One Site to Another Site traceroute #some administrators disable this cmd for security

Jozef Goetz, Important Internet Organizations

Jozef Goetz, Web Resources

Jozef Goetz, Web Resources

Jozef Goetz, Request For Comments (RFCs) – omit it The TCP/IP standards are described in a series of documents, known as the Request for Comments RFCs are first published as the Internet Drafts and are made available to all Internet users for reviewer and feedback by placing them in known RFC repositories After the review process is complete, a draft can become a standard Some RFCs are for information only others are experimental