INTRODUCTION TO NETWORK DEVICES I
Layer 1 devices
Analog modem: it takes the digital signal coming from a digital node and
convert it to an analog signal (modulating the signal) to be placed on the wire. In
return, it accepts the analog signal from the wire and convert it to a digital signal
(demodulating the signal) that the node can understand.
Hub: functions as a repeater (doesn’t care when signal come from or where it
goes). It takes the electrical signal that arrives on a port and replicates that
signal out all of the other ports. It make have a few or many ports.
Layer 2 devices
Switch: utilize an application-specific integrated circuit (ASIC) chip, this chip
allows the switch to know when a device is on the network and which port it is
connected to via that device´s layer 2 MAC address. It make have just a few or
many ports. A switch will only communicate with the local network devices.
Wireles access point (WAP): a specific type of network bridge that connects
wireless network segments with wired network segments. The most common
type WAP bridges 801.11 wriless network segments with 802.3 Ethernet
network segments. A WAP will only communicayes with local network devices.
Layer 3 devices
Multilayer switch (MLS): Provides normal Layer 2 network switching services
but also Layer 3 or higher. The most commong is a Layer 3 switch. It utilizes an
ASIC chip for switching and this chip is also programmed to handle routing
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functions. This allow the device to communicate and pass data to non-local
network devices. It may have a few or many ports.
Router: Is the most common network device for connecting different network
together. The routers uses software programming for decision making as
compared to the switch´s use of an ASIC chip. This programs make it possible
to keep track of different networks and what it considers to be the best possible
route to reach those networks. A router can communicate with both local and
non-local network devices.
INTRODUCTION TO NETWORK DEVICES I (SECURITY DEVICES)
Firewall: A firewall can be placed on routers or hosts (software based) or can
be its own device. It functions at layers 2,3,4 and 7 of the OSI model. It blocks
packets from entering or leaving the network.
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Via stateless inspection: the firewall will examine every packet against
a set of rules. Once the packet matches a rule, the rule is enforced, and
the specified action is taken.
Via stateful inspection: the firewall will only examine the state of the
connection between networks (specially when a connection is made from
an internal network to an external network), the firewall will not examine
any packets returning from the external connection (as a general rule,
external connections are not allowed to be initiated with the internal
network). It is the first line of defense in protecting the internal network
from outside threats.
Instrusion detection sysrem (IDS): is a passive system designed to identify
when a network breach or an attack against the network. Is is designed to
inform a network administrator when a breach or an attack has occurred. It
cannot prevent or stop a breach or an attack. It receveis a copy of all traffic and
evaluates it against a set of standards.
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Signature based: evaluates network traffic for known malware or attack
signatures.
Anomaly based: evaluates network traffic for suspicious changes.
Policy based: evaluates network traffic against a specific declared
security policy.
It may be deployed at the host level (HIDS, Host-based intrusion detection
system).
Intrusion prevention system (IPS): is an active system designed to stop a
breach or attack from succeeding in damaging the network. Will informa a
network administrator. All the traffic on the network flows through the IPS. All
traffic is evaluated against a set of of standards. The best placement is between
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a router (with a firewall) and the destination network segment. It is programmed
to make an active response to the situation (Block the ofending IP address,
terminate the network session, redirect the attack, etc).
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