chapter 5: securing the network infrastructure

Chapter 5: Securing the Network Infrastructure

Security+ Guide to Network Security Fundamentals

Second Edition

Security+ Guide to Network Security Fundamentals, 2e

2

Objectives

• Work with the network cable plant

• Secure removable media

• Harden network devices

• Design network topologies


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Working with the 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

• Thick coaxial cable has a copper wire in center surrounded by a thick layer of insulation that is covered with braided metal shielding


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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 channel protects the core from interference

• BNC connectors: connectors used on the ends of a thin coaxial cable


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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


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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

• Two types:

– Single-mode fiber cables: used when data must be transmitted over long distances

– Multimode cable: supports many simultaneous light transmissions, generated by light-emitting diodes


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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 (continued)

• 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 today’s 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

• Data cannot be changed once recorded


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Optical Media (continued)

• A Compact Disc-Rewriteable (CD-RW) disc can be used to record data, erase it, and record again

• A Digital Versatile Disc (DVD) can store much larger amounts of data

– DVD formats include Digital Versatile Disc-Recordable (DVD-R), which can record once up to 395 GB on a single-sided disc and 79 GB on a double-sided disc


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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


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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 the network

• Basic steps to harden these systems are outlined on page 152


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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 (continued)

• 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 (continued)

• 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

• Page 154 lists defensive controls that can be set for switches and routers


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Hardening Communication Devices

• A second category of network devices are those that communicate over longer distances

• Include:

– Modems

– Remote access servers

– Telecom/PBX Systems

– Mobile devices


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Modems

• Most common communication device

• Broadband is increasing in popularity and can create network connection speeds of 15 Mbps and higher

• Two popular broadband technologies:

– Digital Subscriber Line (DSL) transmits data at 15 Mbps over regular telephone lines

– Another broadband technology uses the local cable television system


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Modems (continued)

• A computer connects to a cable modem, which is connected to the coaxial cable that brings cable TV signals to the home

• Because cable connectivity is shared in a neighborhood, other users can use a sniffer to view traffic

• Another risk with DSL and cable modem connections is that broadband connections are charged at a set monthly rate, not by the minute of connect time


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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 (continued)


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Remote Access Servers (continued)

• 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

• Minimum security features are listed on page 158


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Telecom/PBX Systems

• Term used to describe a Private Branch eXchange

• The definition of a PBX comes from the words that make up its name:

– Private

– Branch

– eXchange


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Mobile Devices

• As cellular phones and personal digital assistants (PDAs) have become increasingly popular, they have become the target of attackers

• Some defenses against attacks on these devices use real-time data encryption and passwords to protect the system so that an intruder cannot “beam” a virus through a wireless connection


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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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• 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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• 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 (IDSs)

• 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 (IDSs) (continued)

• Host-based IDS monitors critical operating system files and computer’s 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

– Result in many false alarms


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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

• For extra security, some networks use a DMZ with two firewalls

• 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 Zones (DMZs) (continued)


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Intranets

• Networks that use the same protocols as the public Internet, but are only accessible to trusted inside users

• Disadvantage is that it does not allow remote trusted users access to information


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Extranets

• Sometimes called a cross between the Internet and an intranet

• Accessible to users that are not trusted internal users, but trusted external users

• Not accessible to the general public, but allows vendors and business partners to access a company Web site


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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)


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Network Address Translation (NAT) (continued)

• 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 attacker’s 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) (continued)


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Virtual LANs (VLANs) (continued)

• 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 network’s 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

chapter 5: securing the network infrastructure

Documents

network security fundamentals

network wire

protected network

network cable plantcable

shieldingthick coaxial

jacketsecurity guide

ecoaxial cablescoaxial

editionsecurity guide