Chapter 10: Networks and Telecommunications

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Fundamentals of Information
Systems Security
Lesson 10
Networks and Telecommunications

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Learning Objective(s)
 Describe networking principles and
security mechanisms.

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Key Concepts
 The OSI Reference Model and its security lapses
 Physical and logical network topologies
 TCP/IP and how it works
 Network security risks and defense tools
 Wireless networks and security controls

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The Open Systems Interconnection
(OSI) Reference Model

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The Main Types of Networks
• Connect systems over a
large geographic area
Wide Area
Networks
• Provide network connectivity
for computers located in the
same geographic area
Local Area
Networks

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Wide Area Networks
 The Internet is an open
network
 Can’t guarantee
privacy
 Consider the security
issues surrounding the
use of an open network
 Develop your own
private WAN

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WAN Connectivity Options
Cable
modem
Digital
subscriber
line (DSL)
Fiber optics
Satellite Dial-up
Cellular 3G
and 4G
networks

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Router Placement

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Local Area Networks (LANs)
 Systems on the same LAN do not
protect themselves from each
other
 Good security is important

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Ethernet Networks
 The Ethernet standard:
• Defines the way that computers communicate on the
network
• Governs both the Physical and Data Link layers
• Defines how computers use MAC addresses to
communicate with each other on the network
 Ethernet has become the most common LAN
technology in use

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LAN Devices: Hubs and Switches
Connect computers on a LAN
Hubs
• Contain a number of plugs (or ports) where you can connect
Ethernet cables for different network systems
• When they hub receive packets, they automatically retransmit
those packets to all the other ports
Switches
• Perform intelligent filtering
• “Know” the MAC address of the system connected to each
port
• When they receive a packet on the network, they look at the
destination MAC address and send the packet only to the port
where the destination system resides

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Virtual LANs (VLANs)
Any broadcast domain that is isolated from
other domains
A collection of logically related network
devices that are viewed as a partitioned
network segment
Used to isolate logical groups of devices to
reduce network traffic and increase security

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TCP/IP and How It Works
A suite of protocols that operate at both the
Network and Transport layers of the OSI
Reference Model
Governs all activity across the Internet and
through most corporate and home networks
Developed by the DoD to provide a highly
reliable and fault-tolerant network
infrastructure (security was not a focus)

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TCP/IP Protocol Suite

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IP Addressing
 IPv4 addresses
• Four-byte (32-bit) addresses that uniquely identify
every device on the network
• Still the most common
 IPv6 addresses
• Are 128 bits long
• Provide more unique device addresses
• Are more secure

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IP Addressing (cont.)
 Dynamic Host Configuration Protocol (DHCP)
• Is used within a network to simplify the
configuration of each user’s computer

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Common Ports
 Network port a number that tells a receiving device where to
send messages it receives
Port Service/Use
20 FTP data transfer
21 FTP control
22 Secure Shell (SSH)
25 Simple Mail Transfer Protocol (SMTP)
53 Domain Name System (DNS)
80 Hypertext Transport Protocol (HTTP)
110 Post Office Protocol v3 (POP3)
139 NetBIOS Session Service
143 Internet Message Access Protocol (IMAP)
443 HTTP over Secure Sockets Layer (SSL)

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Common Protocols
Protocol Common Port(s)
DNS (Domain Name Service) 53
FTP (File Transfer Protocol) 20 (data), 21 (control)
FTPS (FTP over TLS/SSL) 989 (data), 990 (control)
HTTP (Hypertext Transport
Protocol)
80
HTTPS (Hypertext Transport
Protocol over TLS/SSL)
443
iSCSI (Internet Small
Computer System Interface)
860, 3260 (target)

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Common Protocols cont.
Protocol Common Port(s)
NetBIOS (Network Basic
Input/Output System)
137 (Name Service), 138
(Datagram service), 139
(Session service)
SCP (Secure Copy – part of
SSH)
22
SFTP (Secure File Transfer
Protocol – part of SSH)
22
SNMP (Simple Network
Management Protocol)
161
SSH (Secure Shell) 22
Telnet 23
TFTP (Trivial File Transfer
Protocol)
69

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Internet Control Message Protocol
(ICMP)
A management and control protocol for IP
Delivers messages between hosts about
the health of the network
ICMP tools:
• Ping sends a single packet to a target IP
address (ICMP echo request)
• Traceroute uses ICMP echo request packets
to identify the path that packets travel through
a network

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Network Security Risks
 Reconnaissance
• The act of gathering information about a network
for use in a future attack
 Eavesdropping
• When an attacker an attacker taps the data cable
to see all data passing through it
 Denial of service (DoS)
• Flooding a network with traffic and shutting down
a single point of failure

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Network Security Risks (cont.)
 Distributed DoS (DDoS)
• Uses multiple compromised systems to flood the
network from many different directions
 Telephony denial of service (TDoS)
• Attempts to prevent telephone calls from being
successfully initiated or received by some person
or organization

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Basic Network Security Defense
Tools
Firewalls
Virtual private networks and remote access
Network access control (NAC)

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Firewalls
 A firewall controls the flow of traffic by preventing
unauthorized network traffic from entering or leaving a
particular portion of the network

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Firewall Security Features
Flood guard
• Rules can limit traffic bandwidth from hosts, reducing the
ability for any one host to flood a network
Loop protection
• Firewalls can look at message addresses to determine
whether a message is being sent around an unending loop
(for example, from another form of flooding)
Network separation
• Filtering rules enforce divisions between networks, keeping
traffic from moving from one network to another

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Firewall Types
Packet
filtering
Stateful
inspection
Application
proxy

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Firewall-Deployment Techniques
Border firewalls
Screened subnet (or DMZ) firewalls
Multilayered firewalls

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Border Firewall
Separates the protected network from the Internet

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Screened Subnet

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Unified Threat Management (UTM)
URL filter
• Filters web traffic by examining the URL as opposed to
the IP address
Content inspection
• The device looks at some or all network packet content
to determine if the packet should be allowed to pass
Malware inspection
• A specialized form of content inspection, the device
looks at packet content for signs of malware

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Virtual Private Networks and Remote
Access

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Major VPN Technologies
• Point-to-Point Tunneling
Protocol (PPTP)
• Secure Sockets Layer
(SSL) and Transport Layer
Security (TLS)
• Internet Protocol Security
(IPSec)
The three
major VPN
technologies
in use today:

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Network Access Control
Enable you to add more security
requirements before allowing a device to
connect to your network
Perform authentication and posture
checking
IEEE 802.1x standard

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Wireless Networks
Wireless access points (WAPs)
• The connection between a wired and
wireless network
Fences don’t stop wireless signals
Anyone within radio range of wireless
network can capture all data sent on that
network if not encrypted

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Wireless Network Security Controls
VPN over Wireless
Wireless encryption
• WEP (insecure and flawed)
• Counter Mode Cipher Block Chaining
Message Authentication Code Protocol
• Wi-Fi Protected Access (WPA)
SSID broadcast
MAC address filtering

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Additional Wireless Security
Techniques: Hardware
Antenna types
Antenna placement
Power-level controls
Captive portals
Site surveys

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Summary
 The OSI Reference Model and its security
lapses
 Physical and logical network topologies
 TCP/IP and how it works
 Network security risks and defense tools
 Wireless networks and security controls