Transcript File
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 – 49151 : Registered ports Registered for specific purposes 49152 – 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