ARP (Address Resolution Protocol)

Address Resolution Protocol resolves network (IP) addresses to hardware (MAC) addresses. ARP uses the address resolution cache table on every NIC. This table maps IP addresses to MAC addresses on the network. Whenever a node needs to send a packet, it checks the address resolution cache table to see if the MAC address information for the destination is there. If so, that destination address will be used. If not, an ARP request is issued

Go to a DOS prompt and type in ARP /? . You’ll get a list of ARP switches and examples. Type in a switch; use –a or –g. Both of these switches do the same thing: dsplay current ARP entries.

Click here for a more in depth article on ARP
Address Resolution Protocol Spoofing and Man-in-the-Middle Attacks
Click here to read about RARP (Reverse Address Resolution Protocol)

NTP (Network Time Protocol)

NTP sets computer clocks to a standard time source, usually a nuclear clock. This is what keeps all computers on a network set to the same time, which is important for transactions that need time and date stamping. Being out of synch would cause confusion between the server and clients. Without synchronization, transactions can appear to have occurred in the future, which is enough to cause the server to crash.

Click here for a more indepth treatment of NTP.

Here are other TCP/IP protocol resources available on the web:

RadCom Academy’s TCP/IP Protocol Directory
Introduction to the Internet Protocols
Daryl’s TCP/IP Primer
TCP/IP FAQ
TCP/IP Tutorial

2.6 Define the function of TCP/UDP ports. Identify well-known ports.

Both TCP and UDP must use port numbers to communicate with the upper layers. Port numbers keep track of data communication as it streaks across a network. Some of the better known port numbers are:

For a full listing of port numbers, click here.