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DoS
A denial-of-service attack (DoS attack) or distributed denial-of-service attack (DDoS attack) is an attempt to make
a machine or network resource unavailable to its intended users. Perpetrators of DoS attacks typically target sites or
services hosted on high-profile web servers such as banks, credit card payment gateways, and even root name
servers. One common method of attack involves saturating the target machine with external communications
requests, such that it cannot respond to legitimate traffic, or responds so slowly as to be rendered effectively
unavailable.
IGMP
The Internet Group Management Protocol (IGMP) is a communications protocol used by hosts and adjacent routers
on IP networks to establish multicast group memberships. IGMP can be used for online streaming video and
gaming, and allows more efficient use of resources when supporting these types of applications.
IP
The Internet Protocol (IP) is the principal communications protocol used for relaying datagrams (also known as
network packets) across an internetwork using the Internet Protocol Suite. Responsible for routing packets across
network boundaries, it is the primary protocol that establishes the Internet. The Internet Protocol only provides best
effort delivery and its service is characterized as unreliable. Each network device attached to LAN or WAN is
assigned with an IP address. This IP address is used for unique identifier of a network device on the network.
Today, the dominant Internet protocol is IPv4; IPv4 uses 32-bit addresses, which indicates 4 billion, or 4.3×109,
available addresses. Thus IPv6 is brought into use for addressing rapid exhaustion of IP addresses. The IPv6 uses
128-bit addresses, which indicates 340 undecillion, or 3.4×1038 available addresses Yet, IPv4 is still the dominant
protocol of the Internet. Its successor of IPv6 is increasing in use though slow.
MAC Table
An Ethernet device uses a MAC address table for forwarding frames. When forwarding a frame, the device first
looks up the MAC address of the frame in the MAC address table for a match. A switch maintains a MAC address
table for frame forwarding. Each entry in this table maps the MAC address to associated interface. It tells the
switch from which port a MAC address (or host) can be reached. A MAC address table consists of two types of
entries: static and dynamic. Static entries are manually configured by administrators and never age out.
A frame also carries a source MAC address which indicates the sender. The device can automatically populate its
MAC address table by obtaining the source MAC addresses (known as ―MAC address learning‖) of incoming
frames on each port. If a dynamic entry has not updated when the aging timer expires, the device deletes the entry.
PING
Ping is a computer network administration utility used to test the reachability of a host on an Internet Protocol (IP)
network and to measure the round-trip time for messages sent from the originating host to a destination computer.
Ping operates by sending Internet Control Message Protocol (ICMP) echo request packets to the target host and
waiting for an ICMP response. In the process it measures the time from transmission to reception (round-trip time)
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