Kerio Tech Firewall6, Administrator'S Manual

Page: 397 / 404

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Routing table
The information used by routers when making packet forwarding decisions (so called
routes). Packets are routed according to the packet’s destination IP address. On Windows ,
routing table can be printed by the route print command, while on Unix systems ( Linux ,
Mac OS X , etc.) by the
route
command.
Script
A code that is run on the Web page by a client (Web browser). Scripts are used for
generating of dynamic elements on Web pages. However, they can be misused for ads,
exploiting of user information, etc. Modern Web browsers usually support several script
languages, such as JavaScript and Visual Basic Script (VBScript) .
SMTP
Simple Mail Transfer Protocol is used for sending email between mail servers. The SMTP
envelope identifies the sender/recipient of an email.
Spam
Undesirable email message, usually containing advertisments.
Spoofing
Spoofing means using false IP addresses in packets. This method is used by attackers to
make recipients assume that the packet is coming from a trustworthy IP address.
SSL
SSL is a protocol used to secure and encrypt network communication. SSL was origi-
nally designed in order to guarantee secure transfer of Web pages over HTTP protocol.
Nowadays, it is used by almost all standard Internet protocols (SMTP, POP3, IMAP, LDAP,
etc.).
At the beginning of communication, an encryption key is requested and transferred using
asymmetrical encryption. This key is then used to encrypt (symmetrically) the data.
Subnet mask
Subnet mask divides an IP address in two parts: network mask and an address of a host
in the network. Mask have the same form as IP addresses (i.e. 255.255.255.0 ), however,
its value is needed to be understood as a 32-bit number with certain number of ones on
the left end and zeros as the rest. The mask cannot have an arbitrary value. Number one
in a subnet mask represents a bit of the network address and zero stands for a host’s
address bit. All hosts within a particular subnet must have identical subnet mask and
network part of IP address.
TCP
Transmission Control Protocol is a transmission protocol which ensures reliable and se-
quentional data delivery. It establishes so called virtual connections and provides tools
for error correction and data stream control. It is used by most of applications protocols
which require reliable transmission of all data, such as HTTP , FTP , SMTP , IMAP , etc.
TCP protocol uses the following special control information — so called flags :
• SYN (Synchronize) — connection initiation (first packet in each connection)
• ACK (Acknowledgement) — acknowledgement of received data