scis.regis.edu ● CS 468: Advanced UNIX Class 7 Dr. Jesús Borrego Regis University 1

Topics IA Lab visit was scheduled for last week; rescheduled for next week Review of Homework 5 Networking Homework 6 Review for final Q&A 2

Networking Computers connecting to other computers Computers connecting to the Internet Network Topologies Network Devices Internetworking Communicating with Users Data distribution NFS 3

Communication model 4 Communications Infrastructure Source Transmitter Transmission System Receiver Destination

OSI Model 5 Physical Data Link Network Transport Session Presentation Application

Internet Protocol Stack 6 Transport Physical Data Link Control Network/ Internet Transport Application

OSI vs. IP 7 Physical Data Link Network Transport Session Presentation Application Physical Data Link Control Network/ Internet Transport Application

Ethernet Mbps 1 Gbps server Ethernet switch institutional router to institution’s ISP  typically used in companies, universities, etc ▫10 Mbps, 100Mbps, 1Gbps, 10Gbps Ethernet ▫today, end systems typically connect into Ethernet switch

Bridges Connects separate networks ▫One Ethernet network to another one ▫“Bridges” two network segments together ▫Makes it appear as if the two segments were a single one Wire length is limited due to degradation of signal Bridges allow extension of physical limitation of wire 9

Routers Bridges cannot accommodate large networks Routers connect two or more networks ▫“Routes” incoming messages to appropriate network Can be used to connect a LAN to an ISP (Internet Service Provider) Can be used to link the different networks in the global Internet 10

Gateway Used to connect remote LANs to a WAN (Wide Area Network) 11

Topologies Typical LAN topologies include: Bus ▫Single link for all computers Ring (Token) ▫Each computer connected to at least 2 other computers Star ▫Central server 12

Internetworking – Packet Switching 13  sequence of A & B packets has no fixed timing pattern  Time Division Multiplexing (TDM) A B C 100 Mb/s Ethernet 1.5 Mb/s D E statistical multiplexing queue of packets waiting for output link

Internet Address IPv4 – 4 Octets Class A: 0*.*.*.* (two reserved, all 0’s and all 1’s) Class B: 10*.*.*.* Class C: 110*.*.*.* Class D: 111*.*.*.* Class E: 1111*.*.*.* Many subnet calculators available online 14

Ports and common services 15

Users in your system users – local host users rusers - users on local network who – more info than users rwho – more info than rusers w – more information than who whois – information about major internet sites hostname – displays local host name finger – lists information about a user 16

Finger utility 17

User communication on a network write – send individual lines to user talk – interactive split screen two-way chat wall – send messages to all users on local host mail – send messages mesg – disables incoming messages to your terminal 18

File transfer on network Rcp (remote copy) – copy files from one host to another uucp (unix-to-unix copy) – like rcp, copies files between two hosts ftp (file transfer protocol/program) – copy files between local host and other hosts Commands for ftp: UPU page

Distributed access commands rlogin – provides login to remote servers rsh – execute shell commands on remote Unix hosts telnet – executes commands on remote telnet hosts 20

Network File System (NFS) Public domain specification developed by Sun Microsystems Allows you to mount several local file systems into a single network file hierarchy Provides remote mount capability Uses RPC to mount a file system on remote machine 21

Internet control ICANN – Internet Corporation for Assigned Names and Numbers – allocates names and domains ISOC – Internet Society – represents Internet users, technical advisory society IGF – Internet Governance Forum, global forum established by the United Nations in

Network Standards RFC: Request for Comments RFC 114/959: A File Transfer Protocol RFC 791: Internet Protocol RFC 793: Transmission Control Protocol RFC 1945: Hypertext Transfer Protocol HTTP 1.0 RFC 2251: Lightweight Directory Access Protocol RFC 2460: Internet Protocol v6 (IPv6) RFC 4251: Secure Shell (SSH) Protocol Architecture 24

Internet Protocols 26

Internet Protocols 27 BGP - Border Gateway Protocol FTP - File Transfer Protocol HTTP - Hypertext Transfer Protocol ICMP - Internet Control Message Protocol IGMP - Internet Group Management Protocol IP - Internet Protocol MIME - Multipurpose Internet Mail Extension Source: Stallings, W. (2007). Data and computer communications (8th ed.). Upper Saddle River, NJ: Pearson Prentice Hall.

Internet Protocols (Cont’d) 28 OSPF – Open Shortest Path First RSVP – Resource ReSerVation Protocol SMTP – Simple Mail Transfer Protocol SNMP – Simple Network Management Protocol TCP – Transmission Control Protocol UDP – User Datagram Protocol Source: Stallings, W. (2007). Data and computer communications (8th ed.). Upper Saddle River, NJ: Pearson Prentice Hall.

Sample Flow 31 Server Application Presentation Session Transport Network Data Link Physical Data Server Application Presentation Session Transport Network Data Link Physical Data

IPv4 32

IPv6 33

Internet Addressing Media Access Control (MAC): used by hardware IPv4 and IPv6 used by software to determine source, destination, and component location (NIC, not computers) Hostnames used by people Data link layer maps IPs to hardware Hostnames can map names to IPs 34

Sample subnet calculator 35 Source:

CIDR Classless Inter-Domain Routing Netmasks that do not end in a byte boundary Each byte has 8 bits To subnet with 26 bits – not a byte boundary (8, 16, 24), we use the convention /26 37

26 bits6 bits

CIDR Calculator 39 Source:

NAT Private addresses can be used internally by an organization NAT captures internal addresses and prevents them from exiting the corporate environment NAT maintains a table of internal versus external addresses to ensure that no internal addresses escape to the global Internet 42

Routing The process of determining the output path for an incoming packet Routing tables are maintained in the kernel and also in routers throughout the Internet If the server does not know where to send it next, it uses the Address Resolution Protocol to determine next action 44

Routing value in arriving packet’s header routing algorithm local forwarding table header value output link

ARP ARP discovers the hardware address associated with an IP address If the destination address is not in the same network, ARP determines the next hop router If address is not known, it send a broadcast message “Does anybody know where X is?” Response is received and then the protocol uses the response 46

DHCP Dynamic Host Configuration Protocol (RFC 2131) When a host connects to a network, it obtains a ‘lease’ on an IP address, gateways, DNS name servers, Syslog hosts, and others. If the lease is not renewed, it expires 47

DHCP interaction 48 DHCP server: arriving client time DHCP discover src : , 68 dest.: ,67 yiaddr: transaction ID: 654 DHCP offer src: , 67 dest: , 68 yiaddrr: transaction ID: 654 Lifetime: 3600 secs DHCP request src: , 68 dest:: , 67 yiaddrr: transaction ID: 655 Lifetime: 3600 secs DHCP ACK src: , 67 dest: , 68 yiaddrr: transaction ID: 655 Lifetime: 3600 secs

Security Issues Default IP forwarding on a server should be disabled to prevent the server to act as a router ICMP redirect (you should not send packet to me, send to XYZ) can compromise system Source routing can slip through firewalls ▫Do not want to accept or forward source- routed packets 49

Security Issues (Cont’d) IP spoofing means changing source or destination in packet header ▫Receiver may believe source and reply to a malicious server (man-in-the-middle attack) Host-based firewalls are preferred to client- based firewalls VPN – allow remote uses to create ‘tunnels’ to the private network ▫Requires encryption 50

Virtual Private Network (VPN) IP spoofing means changing source or destination in packet header ▫Receiver may believe source and reply to a malicious server (man-in-the-middle attack) Host-based firewalls are preferred to client- based firewalls VPN – allow remote uses to create ‘tunnels’ to the private network ▫Requires encryption 51

52 VPN

Routing Routing has different meanings: ▫Actual forwarding packets ▫Management of routing tables Routing consists of determining the ‘next hop’ in the route towards the destination 63

Routing Daemons Routing daemons collect information from three sources: ▫Configuration files ▫Existing routing tables ▫Routing daemons on other systems Daemons collect this information to determine optimal route and new routes are added to routing tables 65

Homework 6 (last) 1.What is the difference between a bridge, a router, and a gateway? 2.Describe 3 Internet Protocols and provide examples of where they can be used. 3.What are the differences between ftp and rcp? Which one is better and why? 4.Explain how ICMP redirection can cause vulnerabilities in a network. 5.Using an IP subnet calculator of your choice, answer the questions in E14.3 found in the USAH book. Capture the calculator screen. 68

Review for Final Same format as Midterm ▫2 hour, take home ▫8 questions ▫ to by midnight ▫All material from week 4-7 Week 8: 2 hour class, 2 hour take home final 69

Questions? 70