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Glossary
reply packets of connections to other networks or hosts). In contrast to Masquerading, SNAT is a static address
conversion, and the rewritten source address does not need to be one of the firewall's IP addresses. To create
simple connections from private networks to the Internet, you should use the Masquerading function instead of
SNAT.
The use of private IP addresses in combination with Network Address Translation (NAT) in the form of
Masquerading, Source NAT (SNAT), and Destination NAT (DNAT) allows a whole network to hide behind one
or a few IP addresses preventing the identification of your network topology from the outside. With these
mechanisms, Internet connectivity remains available, while it is no longer possible to identify individual
machines from the outside. Using DNAT makes it possible to place servers within the protected network and
still make them available for a certain service.
– A proxy protocol that allows the user to establish a point-to-point connection between the own
SOCKS
network and an external computer via the Internet. Socks, also called Firewall Transversal Protocol, currently
exist at version 5.
– A method of security that requires a firewall to control and track the flow of
Stateful Inspection
communication it receives and sends, and to make TCP/IP-based services decisions (e.g., if it should accept,
reject, authenticate, encrypt and/or log communication attempts). To provide the highest security level possible,
these decisions must be based on the Application State and/or the Communication State (as opposed to
making decisions based on isolated packets). With stateful inspection, a firewall is able to obtain, store,
retrieve, and manipulate information it receives from all communication layers as well as from other
applications. Stateful inspection tracks a transaction and verifies that the destination of an inbound packet
matches the source of a previous outbound request. Other firewall technologies (e.g., packet filters or
application layer gateways) alone may not provide the same level of security as with stateful inspection.
– A directive in a node that tells it to use a certain router or gateway to reach a given IP subnet.
Static Route
The simplest and most common example is the default router/gateway entry entered onto any IP-connected
node (i.e., a static route telling the node to go to the Internet router for all subnets outside of the local subnet).
– The subnet mask or the net mask indicates into which groups the addresses are divided.
Subnet Mask
Based on this arrangement, individual computers are assigned to a network.
– A service run mostly on Unix and Linux systems (but is also available for most other OSes) to track
Syslog
events that occur on the system. Other devices on the network may also be configured to use a given node's
syslog server to keep a central log of what each device is doing. Analysis can often be performed on these logs
using available software to create reports detailing various aspects of the system and/or the network.
TCP (Transmission Control Protocol)
– A widely used connection-oriented, reliable (but insecure)
communications protocol which is the standard transport protocol used on the Internet. TCP is defined in IETF
RFC 793.
– The Internet standard protocol for remote terminal connection service. It is defined in IETF RFC 854
Telnet
and extended with options by many other RFCs.
TLS (Transport Layer Security)
– An open security standard that is similar to SSL3. (Note that some web
sites may not support the TLS protocol.)
– A program available on many systems that traces the path a packet takes to a destination. It is
Trace Route
mostly used to debug routing problems between hosts. A Trace Route protocol is defined in IETF RFC 1393.
– A subnetwork of hosts and routers that can trust each other not to engage in active or
Trusted Subnetwork
passive attacks. It is also assumed that the underlying communications channel such as a LAN is not being
attacked by any other means.
– Transmitting data that is structured in one protocol within the protocol or format of a different
Tunneling
protocol.
– An datagram-oriented unreliable communications protocol widely used on
UDP (User Datagram Protocol)
the Internet. It is a layer over the IP protocol. UDP is defined in IETF RFC 768.
– A UNC path (e.g., \\server) is used to help establish a link to a
UNC (Universal Naming Convention) path
network drive.
URL (Universal Resource Locator)
– URLs are used to describe the location of web pages, and are also
used in many other contexts. An example of an URL is http://www.ssh.com/ipsec/index.html. URLs are defined
in IETF RFCs 1738 and 1808.
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