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CTC 228 – Computer Networks Fall 2015 Instructor: Robert Spengler.

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1 CTC 228 – Computer Networks Fall 2015 Instructor: Robert Spengler

2 Transport Layer Transmission Control Protocol Reliable and connection-oriented User Datagram Protocol Unreliable and connectionless Both work with segments, use source and destination ports, and use checksums

3 Chap 9: More on IP Address Can be STATIC (always the same) or DYNAMIC (changed each time it connects to the network) Frequently assigned by Dynamic Host Configuration Protocol (DHCP)

4 Nmap, my favorite network tool Stands for “Network Mapper” Scans TCP/UDP ports on computers Can determine OS, versions, vulnerabilities, etc. By default nmap scans 1000 most common TCP ports

5 How nmap scans

6 TCP and UDP port assignments 0 – 1023: Well-known ports Reserved for specific uses 1024 – 49151 : Registered ports Registered for specific purposes 49152 – 65535: Ephemeral ports Dynamically allocated

7 Common TCP and UDP Ports 22 (TCP)– SSH 23 (TCP)– Telnet 53 (UDP) – DNS 80 (TCP) – HTTP 443 (TCP) – HTTPS

8 OSI Model Picture Credit: blog.butchevans.com

9 Picture Credit: ieee.org

10 Chapter 1: IP and MAC address IP address is a logical address – IPv4 uses 32-bit addresses – IPv6 uses 128-bit addresses – Use “ipconfig” on Windows to see info – Use “ping” on Windows to test connectivity MAC address is a layer 2 address – MAC address is a 48-bit address

11 Chap 7: In Depth MAC address

12 Chap 1: WAN, LAN, PAN Wide Area Network – connect across broad geographic locations Local Area Network – connect across one local area Personal Area Network – connect immediately surrounding your person

13 Chap 1: Encapsulation

14 Chap 2: A Hub

15 Chap 2: A Switch

16 Chap 7: What could go wrong here?

17 Chap 7: Spanning Tree Protocol STP allows switches to be redundantly linked Allows for reliability in networks STP selectively disables some ports To prevent loops that could cause broadcast storms

18 Chap 2: Tables and Gateways Switches do their magic with MAC tables Routers do their magic with Routing tables These entries can be STATIC or DYNAMIC  Special route: Default Route

19 Chap 3: Unshielded Twisted Pair

20 Chap 3: Ethernet Uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Uses Media Access Control (MAC) addresses  12 Hexadecimal digits One Ethernet protocol data unit is called a frame  Contains source and destination MAC addresses and a error-detecting checksum

21 Chap 3: Ethernet Frame

22 Chap 3: About Collisions and Errors If two devices in the same collision domain send frames at the same time, a collision might occur.  Unlikely with switches but common with hubs. Frames could get mangled on the wire, but since Ethernet is best effort, there is no acknowledgment or verification from receiver.  Errors are detected with a Frame Check Sequence (FCS) added to the end of a frame.

23 Chap 5: Transport Layer Transmission Control Protocol Reliable and connection-oriented User Datagram Protocol Unreliable and connectionless Both work with segments, use source and destination ports, and use checksums

24 Chap 5: TCP and UDP

25 Chap 5: IPv4 Packet

26 Step One: Change the login password

27 Use WPA2 with good password

28 Wifi Channels

29 Wifi Analyzer for Android

30 ARP Find out the layer 2 address associated with a layer 3 address. Broadcast at layer 2 Unicast at layer 3

31 A router automatically knows about directly connected networks

32 Chap 7: RIP/OSPF summary Routing Information Protocol DISTANCE VECTOR Metric is HOP COUNT Periodically sends full routing table Simple, well-supported, but can be inefficient Open Shortest Path First LINK STATE Metric is cost (based on bandwidth) Only sends updates when a change occurs More complex but can be more efficient


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