CTC 228 – Computer Networks Fall 2015 Instructor: Robert Spengler

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

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)

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

How nmap scans

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

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

OSI Model Picture Credit: blog.butchevans.com

Picture Credit: ieee.org

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

Chap 7: In Depth MAC address

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

Chap 1: Encapsulation

Chap 2: A Hub

Chap 2: A Switch

Chap 7: What could go wrong here?

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

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

Chap 3: Unshielded Twisted Pair

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

Chap 3: Ethernet Frame

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.

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

Chap 5: TCP and UDP

Chap 5: IPv4 Packet

Step One: Change the login password

Use WPA2 with good password

Wifi Channels

Wifi Analyzer for Android

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

A router automatically knows about directly connected networks

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