Chapter 5: Securing the Network Infrastructure

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Chapter 5 Securing the Network Infrastructure

• Security Guide to Network Security Fundamentals
• Second Edition

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Objectives

• Work with the network cable plant
• Secure removable media
• Harden network devices
• Design network topologies

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Network Cable Plant

• Cable plant physical infrastructure of a network
  (wire, connectors, and cables) used to carry data
  communication signals between equipment
• Three types of transmission media
• Coaxial cables
• Twisted-pair cables
• Fiber-optic cables

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Coaxial Cables

• Coaxial cable was main type of copper cabling
  used in computer networks for many years
• Has a single copper wire at its center surrounded
  by insulation and shielding
• Called coaxial because it houses two (co) axes
  or shafts?the copper wire and the shielding
• There were two types of coax Ethernet
  installations Thicknet and Thinnet

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Thicknet and Thinnet

• Thicknet, also known as 10Base5 was the first
  coax Ethernet installation.
• The 10 stands for 10Mbps, the Base is for
  baseband signaling and the 5 is 500m signal
  propagation or max. cable run
• Thicknet used vampire taps to add transceivers.
• Thinnet, also known as 10Base2 was the second
  coax Ethernet Installation.
• The 2 in 10Base2 stands for the 185m max. cable
  run rounded up to 2

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Coaxial Cables (continued)

• Thin coaxial cable looks similar to the cable
  that carries a cable TV signal
• A braided copper mesh channel surrounds the
  insulation and everything is covered by an outer
  shield of insulation for the cable itself
• The copper mesh protects the core from
  interference
• BNC connectors connectors used on the ends of a
  thin coaxial cable http//en.wikipedia.org/wiki/BN
  C_connector

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Coaxial Cables (continued)
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Twisted-Pair Cables

• Standard for copper cabling used in computer
  networks today, replacing thin coaxial cable
• Composed of two insulated copper wires twisted
  around each other and bundled together with other
  pairs in a jacket

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Twisted-Pair Cables (continued)

• Shielded twisted-pair (STP) cables have a foil
  shielding on the inside of the jacket to reduce
  interference
• Unshielded twisted-pair (UTP) cables do not have
  any shielding
• Twisted-pair cables have RJ-45 connectors

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Fiber-Optic Cables

• Coaxial and twisted-pair cables have copper wire
  at the center that conducts an electrical signal
• Fiber-optic cable uses a very thin cylinder of
  glass (core) at its center instead of copper that
  transmit light impulses
• A glass tube (cladding) surrounds the core
• The core and cladding are protected by a jacket
• http//en.wikipedia.org/wiki/Fiber_optic
• http//www.jimhayes.com/lennielw/fiber.html

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Fiber-Optic Cables (continued)

• Classified by the diameter of the core and the
  diameter of the cladding
• Diameters are measured in microns, each is about
  1/25,000 of an inch or one-millionth of a meter
  (125 microns)
• Two types
• Single-mode used when data must be transmitted
  over long distances and has a core of about 9
  microns and uses lasers as its light source
• Multimode supports many simultaneous light
  transmissions, generated by light-emitting diodes
  with a core of 62.5 microns

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Securing the Cable Plant

• Securing cabling outside the protected network is
  not the primary security issue for most
  organizations
• Focus is on protecting access to the cable plant
  in the internal network
• An attacker who can access the internal network
  directly through the cable plant has effectively
  bypassed the network security perimeter and can
  launch his attacks at will

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Securing the Cable Plant

• The attacker can capture packets as they travel
  through the network by sniffing
• The hardware or software that performs such
  functions is called a sniffer
• Physical security
• First line of defense
• Protects the equipment and infrastructure itself
• Has one primary goal to prevent unauthorized
  users from reaching the equipment or cable plant
  in order to use, steal, or vandalize it

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Securing Removable Media

• Securing critical information stored on a file
  server can be achieved through strong passwords,
  network security devices, antivirus software, and
  door locks
• An employee copying data to a floppy disk or CD
  and carrying it home poses two risks
• Storage media could be lost or stolen,
  compromising the information
• A worm or virus could be introduced to the media,
  potentially damaging the stored information and
  infecting the network

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Magnetic Media

• Record information by changing the magnetic
  direction of particles on a platter
• Floppy disks were some of the first magnetic
  media developed
• The capacity of todays 3 1/2-inch disks are 14
  MB
• Hard drives contain several platters stacked in a
  closed unit, each platter having its own head or
  apparatus to read and write information
• Magnetic tape drives record information in a
  serial fashion

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Optical Media

• Optical media use a principle for recording
  information different from magnetic media
• A high-intensity laser burns a tiny pit into the
  surface of an optical disc to record a one, but
  does nothing to record a zero
• Capacity of optical discs varies by type
• A Compact Disc-Recordable (CD-R) disc can record
  up to 650 MB of data
• A DVD can record from 4GB to 16GB
• Data cannot be changed once recorded

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Electronic Media

• Electronic media use flash memory for storage
• Flash memory is a solid state storage
  device?everything is electronic, with no moving
  or mechanical parts
• SmartMedia cards range in capacity from 2 MB to
  128 MB
• The card itself is only 45 mm long, 37 mm wide,
  and less than 1 mm thick

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Electronic Media (continued)

• CompactFlash card
• Consists of a small circuit board with flash
  memory chips and a dedicated controller chip
  encased in a shell
• Come in 33 mm and 55 mm thicknesses and store
  between 8MB and 192 MB of data
• USB memory stick is becoming very popular
• Can hold between 8 MB and 1 GB of memory
• USB hard drives range from 5GB to 40GB and above.

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Keeping Removable Media Secure

• Protecting removable media involves making sure
  that antivirus and other security software are
  installed on all systems that may receive a
  removable media device, including employee home
  computers

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Hardening Network Devices

• Each device that is connected to a network is a
  potential target of an attack and must be
  properly protected
• Network devices to be hardened categorized as
• Standard network devices
• Communication devices
• Network security devices

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Hardening Standard Network Devices

• A standard network device is a typical piece of
  equipment that is found on almost every network,
  such as a workstation, server, switch, or router
• This equipment has basic security features that
  you can use to harden the devices

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Workstations and Servers

• Workstation personal computer attached to a
  network (also called a client)
• Connected to a LAN and shares resources with
  other workstations and network equipment
• Can be used independently of the network and can
  have their own applications installed
• Server computer on a network dedicated to
  managing and controlling network services.
• Examples are file servers, print servers and
  Domain Controllers.

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Switches and Routers

• Switch
• Most commonly used in Ethernet LANs
• Receives a packet from one network device and
  sends it to the destination device only
• Limits the collision domain (part of network on
  which multiple devices may attempt to send
  packets simultaneously)
• A switch is used within a single network
• Routers connect two or more single networks to
  form a larger network

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Switches and Routers

• Switches and routers must also be protected
  against attacks
• Switches and routers can be managed using the
  Simple Network Management Protocol (SNMP), part
  of the TCP/IP protocol suite
• Software agents are loaded onto each network
  device to be managed

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Switches and Routers - SNMP

• Each agent monitors network traffic and stores
  that information in its management information
  base (MIB)
• A computer with SNMP management software (SNMP
  management station) communicates with software
  agents on each network device and collects the
  data stored in the MIBs

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Remote Access Servers

• Set of technologies that allows a remote user to
  connect to a network through the Internet or a
  wide area network (WAN)
• Users run remote access client software and
  initiate a connection to a Remote Access Server
  (RAS), which authenticates users and passes
  service requests to the network

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Remote Access Servers
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Remote Access Servers

• Remote access clients can run almost all
  network-based applications without modification
• Possible because remote access technology
  supports both drive letters and universal naming
  convention (UNC) names

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VPNs

• VPN stands for Virtual Private Network
• VPNs come in two flavors
• Site-to-site (also called LAN-to-LAN)
• Remote acess
• Site-to-site VPNs securely connect two or more
  distant locations over the public Internet.
• IPSec and IKE are the two protocols that provide
  authentication, encryption and integrity
  checking.
• Remote access VPNs allow mobile users the ability
  to securely connect from home or on the road to
  the business network.
• Remote access VPNs also use IPSec and IKE but can
  also use SSL connections via their web browser.

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Hardening Network Security Devices

• The final category of network devices includes
  those designed and used strictly to protect the
  network
• Include
• Firewalls
• Intrusion-detection systems
• Network monitoring and diagnostic devices

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Firewalls

• Typically used to filter packets
• Designed to prevent malicious packets from
  entering the network or its computers (sometimes
  called a packet filter)
• Typically located outside the network security
  perimeter as first line of defense
• Can be software or hardware configurations

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Firewalls (continued)

• Software firewall runs as a program on a local
  computer (sometimes known as a personal firewall)
• Enterprise firewalls are software firewalls
  designed to run on a dedicated device and protect
  a network instead of only one computer
• One disadvantage is that it is only as strong as
  the operating system of the computer

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Firewalls (continued)

• Filter packets in one of two ways
• Stateless packet filtering permits or denies
  each packet based strictly on the rule base
• Stateful packet filtering records state of a
  connection between an internal computer and an
  external server makes decisions based on
  connection and rule base
• Can perform content filtering to block access to
  undesirable Web sites

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Firewalls (continued)

• An application layer firewall can defend against
  worms better than other kinds of firewalls
• Reassembles and analyzes packet streams instead
  of examining individual packets

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Intrusion-Detection Systems (IDS)

• Devices that establish and maintain network
  security
• Active IDS (or reactive IDS) performs a specific
  function when it senses an attack, such as
  dropping packets or tracing the attack back to a
  source
• Installed on the server or, in some instances, on
  all computers on the network
• Passive IDS sends information about what
  happened, but does not take action

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Intrusion-Detection Systems (IDS)

• Host-based IDS monitors critical operating system
  files and computers processor activity and
  memory scans event logs for signs of suspicious
  activity
• Network-based IDS monitors all network traffic
  instead of only the activity on a computer
• Typically located just behind the firewall
• Other IDS systems are based on behavior
• Watch network activity and report abnormal
  behavior
• May result in false alarms (false positives)
• http//www.sans.org/resources/idfaq/
• http//www.securityfocus.com/infocus/1670

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Network Monitoring and Diagnostic Devices

• SNMP enables network administrators to
• Monitor network performance
• Find and solve network problems
• Plan for network growth
• Managed device
• Network device that contains an SNMP agent
• Collects and stores management information and
  makes it available to SNMP

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Designing Network Topologies

• Topology physical layout of the network devices,
  how they are interconnected, and how they
  communicate
• Essential to establishing its security
• Although network topologies can be modified for
  security reasons, the network still must reflect
  the needs of the organization and users

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Security Zones

• One of the keys to mapping the topology of a
  network is to separate secure users from
  outsiders through
• Demilitarized Zones (DMZs)
• Intranets
• Extranets

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Demilitarized Zones (DMZs)

• Separate networks that sit outside the secure
  network perimeter
• Outside users can access the DMZ, but cannot
  enter the secure network
• The types of servers that should be located in
  the DMZ include
• Web servers
• E-mail servers
• Remote access servers
• FTP servers

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Demilitarized Zone (DMZ)
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Network Address Translation (NAT)

• You cannot attack what you do not see is the
  philosophy behind Network Address Translation
  (NAT) systems
• Hides the IP addresses of network devices from
  attackers
• Computers are assigned special IP addresses
  (known as private addresses)
• RFC 1918 addresses
• 10.0.0.0 10.255.255.255
• 172.16.0.0 172.31.255.255
• 192.168.0.0 192.168.255.255

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Network Address Translation (NAT)

• These IP addresses are not assigned to any
  specific user or organization anyone can use
  them on their own private internal network
• Port address translation (PAT) is a variation of
  NAT
• Each packet is given the same IP address, but a
  different TCP port number

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Honeypots

• Computers located in a DMZ loaded with software
  and data files that appear to be authentic
• Intended to trap or trick attackers
• Two-fold purpose
• To direct attackers attention away from real
  servers on the network
• To examine techniques used by attackers

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Honeypots (continued)
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Virtual LANs (VLANs)

• Segment a network with switches to divide the
  network into a hierarchy
• Core switches reside at the top of the hierarchy
  and carry traffic between switches
• Workgroup switches are connected directly to the
  devices on the network
• Core switches must work faster than workgroup
  switches because core switches must handle the
  traffic of several workgroup switches

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Virtual LANs (VLANs)
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Virtual LANs (VLANs)

• Segment a network by grouping similar users
  together
• Instead of segmenting by user, you can segment a
  network by separating devices into logical groups
  (known as creating a VLAN)

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Summary

• Cable plant physical infrastructure (wire,
  connectors, and cables that carry data
  communication signals between equipment)
• Removable media used to store information
  include
• Magnetic storage (removable disks, hard drives)
• Optical storage (CD and DVD)
• Electronic storage (USB memory sticks, FlashCards)

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Summary (continued)

• Network devices (workstations, servers, switches,
  and routers) should all be hardened to repel
  attackers
• A networks topology plays a critical role in
  resisting attackers
• Hiding the IP address of a network device can
  help disguise it so that an attacker cannot find
  it