Glossary of Terms Modified from http://www.kerio.com/manual/wrp/en/418.htm ARP Address Resolution Protocol associates an IP address to a hardware address called a Media Access Control (MAC) address. BOOTP The Bootstrap Protocol is a variant of DHCP. Clients must be enabled to use this protocol. DHCP Dynamic Host Configuration Protocol is a protocol for organizing and simplifying the administration of IP configuration for computers in a network. A DHCP server such as Linux maintains the settings that are issued to each client within the network that is configured as a DHCP client. These settings define, among other things, where the client must send requests for Domain Name resolution and to whom the client should send all IP traffic that it does not know how to route. DNS Domain Name System is a naming scheme for IP addressing. For example http://www.lugod.org is a domain name and has an associated IP address. A DNS server matches domain names to an IP address. We use the domain name system because it is easier to remember a domain name than a string of numbers. Firewall A filtering module located on a gateway machine that examines all incoming and outgoing traffic to determine if it may be routed to its destination. FTP and SFTP File Transfer Protocol is an application protocol used to transfer, update, delete, move, rename or copy data across the internet. SFTP is the OpenSSH version of FTP. Gateway The point of entrance from one network to another. A gateway is responsible for the proper distribution of data coming in and going out of a local area network. IP address IPv4 An IP address is a unique 32-bit number, which identifies a computer in an IP network. LAN A Local Area Network (LAN) is a group of interconnected computers with the ability to share resources. MAC address Media Access Control address is more specific than an IP address and cannot be changed because it is specific to each network hardware device. NAT NAT - Network Address Translation - also called IP masquerade, is a process of translating the source header of IP packets so they will be routable across wide area networks. Network interface A network interface is any device that connects a computer with other computers by means of a communication medium. A network interface may be an Ethernet card, modem, ISDN card, etc. The computer sends and receives data by means of a network interface. Network Mask Network mask is used to group IP addresses together. There is a group of addresses assigned to each network segment. For example, the mask 255.255.255.0 groups together 254 IP addresses. If we have, as another example, a sub-network 192.168.16.64 with mask 255.255.255.224, the addresses we may assign to computers on the sub-network are 192.168.16.65 to 192.168.16.94, with a broadcast address of 192.168.16.95. Packet A packet is a basic communication data unit used when transmitting information from one computer to another. The maximum length of a packet depends on the communication medium. As an example, in Ethernet networks the maximum length is1500 bytes. A data packet can be divided into two parts: the header part and the data part. The header contains information needed for communication between nodes; the data is the body of the packet that is ultimately received by the application. POP3 The (Post Office Protocol) POP3 protocol is a TCP protocol using port 110. It is used to gather email. Linux cam function as both a POP3 server and client. Port A port is a 16-bit number (the allowed range being 1 through 65535) used by the TCP and UDP protocols at the transport layer. Ports are used to address applications (services) that run on a computer. If there was only a single network application running on the computer, there would be no need for port numbers and the IP address only would suffice for addressing services. However, several applications may run at once on a particular computer and we need to differentiate among them. This is what port numbers are used for. Thus, a port number may be seen as an address of an application within the computer. Port Mapping Port mapping (or Port Address Translation - PAT) is the process where packets arriving to a particular IP address/port can be translated and thus redirected to a different IP/port. This functionality is a way to create a persistent passage through NAT. Port Mapping is only necessary for incoming connections, not returning traffic. Protocol Defines rules for the transmission of data. Proxy Proxy is another method of sharing of Internet access. Proxy operates with the data on a higher protocol level so that Internet sharing with Proxy servers was never reliable and also required a special application gateway for each networking protocol. SMTP The Simple Mail Transfer Protocol (SMTP) protocol is a TCP protocol that uses port 25. All email is sent using SMTP. SMTP servers inspect the email header and may generate more pieces of the same email if there are multiple recipients. The destination address is analyzed and either delivered to a local mail box or forwarded to another SMTP server. When the email reaches the SMTP server occupying the domain for which the email was intended, the email is stripped of specific header information and delivered to a local user account, whereupon the user must initiate a connection to the server to access the email via POP3, IMAP, or HTTP. TCP/IP TCP/IP is a sum of networking protocols used for communication across wide area networks such as the Internet. UDP (User Datagram Protocol) Uses a special type of packet called a datagram. Datagrams do not require a response; they are one way only (connectionless). Datagrams are usually used for streaming media because an occasional packet loss will not affect the final product of the transmission. VPN Virtual Private Networking allows local area networks to communicate across wide area networks, typically over an encrypted channel.