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Appendix D. Definitions of terms
Relay
When the local network is connected to the Internet through a firewall, all types of services are usually
blocked. It is as if the network is not connected to the Internet. Relays can then be set up to allow certain
services, such as the WWW, to pass through under controlled circumstances. Think of it as a giant stone wall
with a gate and a specialized gate keeper. The gate keeper only lets certain visitors pass. To allow others to
pass through, you set up another gate with another specialized gate keeper.
RFC
An RFC (Request For Comments) is a document which standardizes some aspect of the Internet traffic. RFC:s
are available at http://www.rfc-editor.org/rfcsearch.html.
RIP
RIP is a protocol that manages dynamic routing. Dynamic routing means that the path for traffic can be
changed. RIP selects the path that goes through the least number of routers, but does not consider the
bandwidth or load on the network. RIP is only used in local networks. Fixed paths for traffic are called static
routing.
Router
A router is a machine that is used to connect several smaller and larger networks. Often, a router is used to
connect a local network to the Internet. This router only lets traffic to the Internet out; all other traffic remains
on the local network. A router can also be called a gateway.
Routing
A routing is a path for the traffic between different computers.
Server
A server can be a program that performs a service on a network or a computer that runs one or more server
programs. One example is a computer that stores files centrally, which makes it a kind of server, usually called
a file server. The program that manages traffic so that people from the outside can access an organization’s
web pages is a server program.
SIP
SIP, Session Initiation Protocol, is a protocol for creating, maintaining and terminating various media stream
sessions over an IP network. SIP is used to negotiate which media streams the parts can send and receive, and
which parts should be involved in the exchange. When this is established, the media streams are sent according
to their own protocols (e.g. HTTP). A thorough description of SIP can be found in RFC 2543.
SLIP
SLIP stands for Serial Line IP. This is usually used to send IP packets over modem connections. See IP.
SLIRP
SLIRP is a program that sends IP packets over serial connections, such a modem connections. SLIRP is run as
a user program. SLIRP does not need its own IP address; it uses the server’s IP address. The program works
with both SLIP and PPP clients. See IP.
SMTP
Simple Mail Transfer Protocol, a protocol for sending e-mail between e-mail servers. SMTP uses port 25.
SNMP
A protocol used for network monitoring. SNMP uses ports 161 and 162.
Sockets
When two computers connect to each other, they use their IP addresses and port numbers. The combination of
an IP address and a port number is called a socket. See IP addresses and Ports.
SSH, Secure SHell
SSH is a system for secure, encrypted connections between two computers over a network. SSH uses one open
and one secret key. In contrast to Kerberos, SSH does not use a central server for security. SSH uses port 22.
SSL
SSL stands for Secure Sockets Layer. The SSL protocol handles establishing of encrypted computer
connections. Usually HTTP and WWW traffic is sent on SSL. HTTP on SSL is called HTTPS.
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