| Network Devices | ISO OSI Model | Dialup Connections | Port Assignments | IEEE 802 Standards | RAID | Troubleshooting Utilities | Troubleshooting Tools |
| MAU Multistation access unit. | Acts as a hub in Token ring networks. |
| Repeater | Used to extend a segment beyond the limitation of the maximum allowed cable length and boost the signal between two cable segments. Repeaters can connect segments with different physical media such as UTP and Coaxial cable. Repeaters can't connect different network network architecture such as Ethernet and token ring. |
| Bridge | Used to segment a network and reduce network traffic by examining the source and destination hardware address of the packet. Only Translation bridges can connect dissimilar network architectures like Ethernet and token ring. |
| Router | Used to route packets to remote networks by examining the packet's network source and destination address. Routers reduce broadcast storms because they don't route broadcast packets. Routers can connect dissimilar network architectures. The destination address of the packet must match an entry in the routing table of the router; otherwise, the packet is discarded. |
| Brouter | A combination of Router and a Bridge. Used on networks that have both routable and non-routable protocols. |
| Gateway | Used to connect networks with different protocols like TCP/IP network and IPX/SPX networks. |
| Proxy Server | Used to isolate internal network computers from the internet. When users on the network want to access the Internet , they first access the Proxy server and the proxy server accesses the internet and retrieves the requested web page or document. The user then gets a copy of that page from the proxy server. Only IP address of the proxy server goes out to the internet. Proxy server will also cache frequently used sites to speed up future access. Can also be configured to restrict access to certain sites. |
| Firewall | Used to prevent unauthorized access from the external network such as internet to your local network. Microsoft Proxy server has the ability to act as a firewall. |
| OSI layer | What the layer is responsible for | Devices | Protocol |
| Physical | The physical layer of a network, including the processes that convert bits into signals for sending and signals to bits for receiving. | Hubs, Repeaters, Amplifiers, Transceivers, | None |
| Datalink | Data is formated into packets. Provides error checking, correction, and the avoidance of transmission conflicts. If CRC fails at receiving computer, this layer will request retransmission. Mac addresses are also resolved. | Bridges, Switches. | |
| Network | Handles addressing of data for delivery and converting network addresses into physical addresses. Routes messages. | Routers | IP, IPX, RIP |
| Transport | Network messages are chopped into smaller pieces for transmission and reassembled at their destination. It supports delivery, error detection and recovery. | Gateways | TCP, UDP. |
| Session | Responsible for opening, using and closing the session. Manages simple, half, and full duplex dialogues between computers. | Gateways Network file system, | SQL, RPC. |
| Presentation | Translating data into understandable format for transmission. Data compression and encryption takes place at this layer. | Gateways | SNMP, FTP, TELNET, WWW, HTTP. |
| Application | This layer interfaces with applications that want to gain access to the network. | Gateways |
| Serial Line Internet Protocol (SLIP) | Supports only TCP/IP protocol. Does not support compression or encryption. Provides no mechanism for error checking. |
| Point -to- Point Protocol (PPP) | Supports IPX/SPX, TCP/IP , NetBEUI, AppleTalk. Supports compression and error checking. Functions at physical and Datalink layer and virtually turns a modem into a NIC card. |
| Point -to- Point Tunneling Protocol (PPTP) | Allows establishing a secure encrypted communication over TCP/IP network. PPTP is used to establish virtual private network over the internet. |
| Port Number | Assignment |
| 20 | FTP Data Transfer |
| 25 | SMTP (Simple Mail Transfer Protocol) |
| 53 | DNS (Domain Name System) |
| 80 | HTTP (Hyper Text Transfer Protocol) |
| 110 | POP3 (Post Office Protocol) |
| 802.1 | Internetworking |
| 802.2 | Logical link control |
| 802.3 | Ethernet (CSMA/CD) |
| 802.4 | Token bus LAN |
| 802.5 | Token Ring BUS |
| 802.12 | Demand Priority. Like 100VG-Any LAN |
| 0 | Disk Striping without parity. Minimum 2 disks. No fault tolerance. Improves read/write speed. |
| 1 | Disk Mirroring and Disk Duplexing Minimum 2 disks. For disk duplexing minimum 2 disks and 2 controllers. GOOD FAULT TOLERANCE. Can be more than 2 disks. |
| 2 | Disk Striping with Error correction code |
| 3 | Disk striping with error correction code stored as parity |
| 4 | Disk striping with large blocks allocation. |
| 5 | Disk Striping with Parity Minimum 3 maximum 32 disks. Fault tolerant, less expensive than disk mirroring. If more than one disk fails, data can't be recovered. |
| WINIPCFG | To see TCP/IP configuration of your computer. Will display your IP address, subnet mask, default gateway, hardware MAC address. Used from command prompt on windows 95/98. Very useful if your computer is obtaining It's IP address from DHCP server and you need to find out what IP address has been assigned to you. |
| IPCONFIG | Same function as WINIPCFG, used on NT computers Only used on NT machines. For more detailed information use with a switch IPCONFIG /ALL |
| NETSTAT | Will display your current TCP/IP session including addresses of hosts connected to your computer and port numbers. Can be used when you want to find out who's communicating with your computer. Looking at port number will reveal what service being used. Can be useful if you suspect that someone is connected to your computer without authorization. |
| TRACERT | Will display a report that lists all routers and networks that the packet must travel to get to it's destination and the time in milliseconds that packet takes to travel between routers. Very useful when trying to find a bottleneck in your network. |
| PING | Used to verify connection between your computer and remote host. You can ping a host using it's IP address or it's host name. This is the first utility you should use when you have connection problem. If you can ping a host by IP address but can't by it's name then you have a problem with name resolution. |
| ARP | Will display hardware addresses of local hosts on the network. Entries will remain in ARP cache for 10 minutes on windows NT Can use this command if you suspect invalid ARP entries in ARP cache. |
| Digital Voltmeter | Simple inexpensive tool. Can be used to determine if the cable is faulty. Can be used to test power supply voltage. |
| TDR | time domain reflectometer Sends signals on to the cable and listens for the echo to come back. Can be used to determine the distance to the break in the cable. Special TDR can be used to find a break in fiber optic cable. Advance cable tester Has functions of Digital voltmeter, TDR plus can analyze network traffic, find excessive collisions. |
| Protocol Analyzer | Most advanced and expensive tool. Can look inside packets. Can be used to find faulty NIC cards, faulty routers and bridges. |
| Loopback Adapter | External loopback adapter can be used to test NIC card without connecting the card to the network. Software loopback adapter can be used when you need to install and set up network protocols in computer that does not have a NIC card. When installing windows NT an a computer without a NIC card, you must PICK "Loopback adapter" from the list of NIC cards or you will not be able to install protocols. |
| Terminator | Can be used to help find a break in the cable. |
More info: www.cert21.com