Devices

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Devices

• Chapter 9

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Learning Objectives

• Understand the purpose of a network firewall and
  the kinds of firewall technology available on the
  market
• Understand the role of routers, switches, and
  other networking hardware in security
• Determine when VPN or RAS technology works to
  provide a secure network connection

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Firewalls

• Hardware or software device that provides means
  of securing a computer or network from unwanted
  intrusion
• Dedicated physical device that protects network
  from intrusion
• Software feature added to a router, switch, or
  other device that prevents traffic to or from
  part of a network

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Management Cycle forFirewall Protection

1. Draft a written security policy
2. Design the firewall to implement the policy
3. Implement the design by installing selected
   hardware and software
4. Test the firewall
5. Review new threats, requirements for additional
   security, and updates to systems and software
   repeat process from first step

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Drafting a Security Policy

• What am I protecting?
• From whom?
• What services does my company need to access over
  the network?
• Who gets access to what resources?
• Who administers the network?

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Available Targets and Who Is Aiming at Them

• Common areas of attack
• Web servers
• Mail servers
• FTP servers
• Databases
• Intruders
• Sport hackers
• Malicious hackers

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Who Gets Access to Which Resources?

• List employees or groups of employees along with
  files and file servers and databases and database
  servers they need to access
• List which employees need remote access to the
  network

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Who Administers the Network?

• Determine individual(s) and scope of individual
  management control

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Designing the Firewallto Implement the Policy

• Select appropriate technology to deploy the
  firewall

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What Do Firewalls Protect Against?

• Denial of service (DoS)
• Ping of death
• Teardrop or Raindrop attacks
• SYN flood
• LAND attack
• Brute force or smurf attacks
• IP spoofing

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How Do Firewalls Work?

• Network address translation (NAT)
• Basic packet filtering
• Stateful packet inspection (SPI)
• Access control lists (ACL)

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Network Address Translation (NAT)

• Only technique used by basic firewalls
• Enables a LAN to use one set of IP addresses for
  internal traffic and a second set for external
  traffic
• Each active connection requires a unique external
  address for duration of communication
• Port address translation (PAT)
• Derivative of NAT
• Supports thousands of simultaneous connections on
  a single public IP address

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Basic Packet Filtering

• Firewall system examines each packet that enters
  it and allows through only those packets that
  match a predefined set of rules
• Can be configured to screen information based on
  many data fields
• Protocol type
• IP address
• TCP/UDP port
• Source routing information

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Stateful Packet Inspection (SPI)

• Controls access to network by analyzing
  incoming/outgoing packets and letting them pass
  or not based on IP addresses of source and
  destination
• Examines a packet based on information in its
  header
• Enhances security by allowing the filter to
  distinguish on which side of firewall a
  connection was initiated essential to blocking
  IP spoofing attaches

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Access Control Lists (ACL)

• Rules built according to organizational policy
  that defines who can access portions of the
  network
• Access-list 101 permit tcp any 1.2.1.222 0.0.0.0
  eq 80
• Access-list 101 deny ip any 1.2.1.222 0.0.0.0

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Routers

• Network management device that sits between
  network segments and routes traffic from one
  network to another
• Allows networks to communicate with one another
• Allows Internet to function
• Act as digital traffic cop (with addition of
  packet filtering)

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How a Router Moves Information

• Examines electronic envelope surrounding a
  packet compares address to list of addresses
  contained in routers lookup tables
• Determines which router to send the packet to
  next, based on changing network conditions

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How a Router Moves Information
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Beyond the Firewall

• Demilitarized zone (DMZ)
• Bastion hosts (potentially)

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Demilitarized Zone

• Area set aside for servers that are publicly
  accessible or have lower security requirements
• Sits between the Internet and internal networks
  line of defense
• Stateful device fully protects other internal
  systems
• Packet filter allows external traffic only to
  services provided by DMZ servers
• Allows a company to host its own Internet
  services without sacrificing unauthorized access
  to its private network

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Bastion Hosts

• Computers that reside in a DMZ and that host Web,
  mail, DNS, and/or FTP services
• Gateway between an inside network and an outside
  network
• Defends against attacks aimed at the inside
  network used as a security measure
• Unnecessary programs, services, and protocols are
  removed unnecessary network ports are disabled
• Do not share authentication services with trusted
  hosts within the network

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Application Gateways

• Also known as proxy servers
• Monitor specific applications (FTP, HTTP, Telnet)
• Allow packets accessing those services to go to
  only those computers that are allowed
• Good backup to packet filtering

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Application Gateways

• Security advantages
• Information hiding
• Robust authentication and logging
• Simpler filtering rules
• Disadvantage
• Two steps are required to connect inbound or
  outbound traffic can increase processor overhead

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OSI Reference Model

• Architecture that classifies most network
  functions
• Seven layers
• Application
• Presentation
• Session
• Transport
• Network
• Data-Link
• Physical

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The OSI Stack

• Layers 4 and 5
• Where TCP and UDP ports that control
  communication sessions operate
• Layer 3
• Routes IP packets
• Layer 2
• Delivers data frames across LANs

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Limitations of Packet-Filtering Routers

• ACL can become long, complicated, and difficult
  to manage and comprehend
• Throughput decreases as number of rules being
  processed increases
• Unable to determine specific content or data of
  packets at layers 3 through 5

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Switches

• Provide same function as bridges (divide
  collision domains), but employ application-specifi
  c integrated circuits (ASICs) that are optimized
  for the task
• Reduce collision domain to two nodes (switch and
  host)
• Main benefit over hubs
• Separation of collision domains limits the
  possibility of sniffing

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Switches
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Switch Security

• ACLs
• Virtual Local Area Networks (VLANs)

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Virtual Local Area Network

• Uses public wires to connect nodes
• Broadcast domain within a switched network
• Uses encryption and other security mechanisms to
  ensure that
• Only authorized users can access the network
• Data cannot be intercepted
• Clusters users in smaller groups
• Increases security from hackers
• Reduces possibility of broadcast storm

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Security Problems with Switches

• Common ways of switch hijacking
• Try default passwords which may not have been
  changed
• Sniff network to get administrator password via
  SNMP or Telnet

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Securing a Switch

• Isolate all management interfaces
• Manage switch by physical connection to a serial
  port or through secure shell (SSH) or other
  encrypted method
• Use separate switches or hubs for DMZs to
  physically isolate them from the network and
  prevent VLAN jumping

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Securing a Switch

• Put switch behind dedicated firewall device
• Maintain the switch install latest version of
  software and security patches
• Read product documentation
• Set strong passwords

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Quick Quiz

• The process by which a private IP address in a
  corporate network is translated into a public
  address by a router or firewall is
  called_____________
• True or False Advanced firewalls use stateful
  packet inspection to improve security.
• A computer providing public network services that
  resides inside a corporate network but outside
  its firewall is called a ______.
• True or False IP packets are routed by layer 2
  of the OSI model.
• A feature available in some switches that permit
  separating the switch into multiple broadcast
  domains is called _________.

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Wireless

• Almost anyone can eavesdrop on a network
  communication
• Encryption is the only secure method of
  communicating with wireless technology

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Modems
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DSL versus Cable Modem Security

• DSL
• Direct connection between computer/network and
  the Internet
• Cable modem
• Connected to a shared segment party line
• Most have basic firewall capabilities to prevent
  files from being viewed or downloaded
• Most implement the Data Over Cable Service
  Interface Specification (DOCSIS) for
  authentication and packet filtering

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Dynamic versus Static IP Addressing

• Static IP addresses
• Provide a fixed target for potential hackers
• Dynamic IP addresses
• Provide enhanced security
• By changing IP addresses of client machines, DHCP
  server makes them moving targets for potential
  hackers
• Assigned by the Dynamic Host Configuration
  Protocol (DHCP)

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Remote Access Service (RAS)

• Provides a mechanism for one computer to securely
  dial in to another computer
• Treats modem as an extension of the network
• Includes encryption and logging
• Accepts incoming calls
• Should be placed in the DMZ

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Security Problems with RAS

• Behind physical firewall potential for network
  to be compromised
• Most RAS systems offer encryption and callback as
  features to enhance security

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Telecom/Private Branch Exchange (PBX)

• PBX
• Private phone system that offers features such as
  voicemail, call forwarding, and conference
  calling
• Failure to secure a PBX can result in toll fraud,
  theft of information, denial of service, and
  enhanced susceptibility to legal liability

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IP-Based PBX
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PBX Security Concerns

• Remote PBX management
• Hoteling or job sharing
• Many move codes are standardized and posted on
  the Internet

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Virtual Private Networks

• Provide secure communication pathway or tunnel
  through public networks (eg, Internet)
• Lowest levels of TCP/IP are implemented using
  existing TCP/IP connection
• Encrypts either underlying data in a packet or
  the entire packet itself before wrapping it in
  another IP packet for delivery
• Further enhances security by implementing
  Internet Protocol Security (IPSec)

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Intrusion Detection Systems (IDS)

• Monitor networks and report on unauthorized
  attempts to access any part of the system
• Available from many vendors
• Forms
• Software (computer-based IDS)
• Dedicated hardware devices (network-based IDS)
• Types of detection
• Anomaly-based detection
• Signature-based detection

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Computer-based IDS

• Software applications (agents) are installed on
  each protected computer
• Make use of disk space, RAM, and CPU time to
  analyze OS, applications, system audit trails
• Compare these to a list of specific rules
• Report discrepancies
• Can be self-contained or remotely managed
• Easy to upgrade software, but do not scale well

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Network-based IDS

• Monitors activity on a specific network segment
• Dedicated platforms with two components
• Sensor
• Passively analyzes network traffic
• Management system
• Displays alarm information from the sensor

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Anomaly-based Detection

• Builds statistical profiles of user activity and
  then reacts to any activity that falls outside
  these profiles
• Often leads to large number of false positives
• Users do not access computers/network in static,
  predictable ways
• Cost of building a sensor that could hold enough
  memory to contain the entire profile and time to
  process the profiles is prohibitively large

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Signature-based Detection

• Similar to antivirus program in its method of
  detecting potential attacks
• Vendors produce a list of signatures used by the
  IDS to compare against activity on the network or
  host
• When a match is found, the IDS take some action
  (eg, logging the event)
• Can produce false positives normal network
  activity may be construed as malicious

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Network Monitoring and Diagnostics

• Essential steps in ensuring safety and health of
  a network (along with IDS)
• Can be either stand-alone or part of a
  network-monitoring platform
• HPs OpenView
• IBMs Netview/AIX
• Fidelias NetVigil
• Aprismas Spectrum

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Ensuring Workstation andServer Security

• Remove unnecessary protocols such as NetBIOS or
  IPX
• Remove unnecessary user accounts
• Remove unnecessary shares
• Rename the administrator account
• Use strong passwords

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Personal Firewall Software Packages

• Offer application-level blocking, packet
  filtering, and can put your computer into stealth
  mode by turning off most if not all ports
• Many products available, including
• Norton Firewall
• ZoneAlarm
• Black Ice Defender
• Tiny Softwares Personal Firewall

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Firewall Product Example
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Antivirus Software Packages

• Necessary even on a secure network
• Many vendors, including
• McAffee
• Norton
• Computer Associates
• Network Associates

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Mobile Devices

• Can open security holes for any computer with
  which these devices communicate

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Chapter Summary

• Virtual isolation of a computer or network by
  implementing a firewall through software and
  hardware techniques
• Routers
• Switches
• Modems
• Various software packages designed to run on
  servers, workstations, and PDAs

continued
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Chapter Summary

• Virtual private networks (VPNs)
• Private branch exchanges (PBX)
• Remote Access Services (RAS)

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Quick Quiz

• The standard used to help secure cable modem
  communications is called ____________
• True or False Static IP addressing is the most
  secure form of addressing.
• True or False RAS should be placed in the DMZ.
• A _____________ is used to provide a secure
  communication channel through the public Internet
• ______________ based IDS uses statistical
  profiles.