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Spam
Undesirable email message, usually containing advertisments.
Spoofing
Spoofing means using false IP addresses in packets. This method is used by at-
tackers 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
originally designed by Netscape in order to ensure secure transfer of Web pages
over HTTP protocol. Nowadays, it is used by most 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 ad-
dress 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 net-
work 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
sequentional 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
• RST (Reset) — request on termination of a current connection and on initiation
of a new one
• URG (Urgent) — urgent packet
• PSH (Push) — request on immediate transmission of the data to upper TCP/IP
layers
• FIN (Finalize) — connection finalization