Chapter 5: Securing the Network Infrastructure

Security+ Guide to Network Security FundamentalsSecond Edition

Objectives

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

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

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

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

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/BNC_connector

Coaxial Cables (continued)

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

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

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

jackethttp://en.wikipedia.org/wiki/Fiber_optic

http://www.jimhayes.com/lennielw/fiber.html

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

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

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

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

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

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

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

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.

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

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

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

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.

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

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

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

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

Remote Access Servers

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

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.

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

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

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

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

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

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

Intrusion-Detection Systems (IDS)

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• May result in false alarms (false positives)http://www.sans.org/resources/idfaq/ http://www.securityfocus.com/infocus/1670

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

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

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

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

Demilitarized Zone (DMZ)

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

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

Network Address Translation (NAT)

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

Honeypots (continued)

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

Virtual LANs (VLANs)

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)

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)

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