chapter 10 introduction to network securitysjkuyath/etee3281/ch10.pdf · •develop a network...

Chapter 10

Introduction to Network Security

Objectives

• Develop a network security policy

• Secure physical access to network

equipment

• Secure network data

• Use tools to find network security

weaknesses

Guide to Networking Essentials, Fifth Edition 2

Network Security Overview and Policies

• Perceptions of network security vary depending on:– People– Industry

• Network security should be as unobtrusive as possible, allowing network users to concentrate on the tasks they want to accomplish, rather than how to get to the data they need to perform those tasks

• A company that can demonstrate its information systems are secure is more likely to attract customers, partners, and investors


Developing a Network Security Policy

• A network security policy describes the rules

governing access to a company’s information

resources, the enforcement of those rules, and

the steps taken if rules are breached

– Should also describe the permissible use of those

resources after they’re accessed

– Should be easy for ordinary users to understand and

reasonably easy to comply with

– Should be enforceable

– Should clearly state the objective of each policy so that

everyone understands its purpose


Elements of a Network Security Policy

• Elements (minimum for most networks)

– Privacy policy

– Acceptable use policy

– Authentication policy

– Internet use policy

– Access policy

– Auditing policy

– Data protection

• Security policy should protect organization legally

• Security policy should be continual work in progress


Understanding Levels of Security

• Security doesn’t come without a cost

• Before deciding on a level of security, answer:

– What must be protected?

– From whom should data be protected?

– What costs are associated with security being breached and data being lost or stolen?

– How likely is it that a threat will actually occur?

– Are the costs to implement security and train users to use a secure network outweighed by the need to provide an efficient, user-friendly environment?

• Levels: highly restrictive, moderately restrictive, open


Highly Restrictive Security Policies

• Include features such as:– Data encryption, complex password requirements,

detailed auditing and monitoring of computer and network access, intricate authentication methods, and policies that govern use of the Internet/e-mail

• Might require third-party hardware and software

• High implementation expense– High design and configuration costs for SW and

HW

– Staffing to support the security policies

– Lost productivity (high learning curve for users)

• Used when cost of a security breach is high


Moderately Restrictive Security Policies

• Most organizations can opt for this type of policy

• Requires passwords, but not overly complex ones

• Auditing detects unauthorized logon attempts, network resource misuse, and attacker activity– Most NOSs contain authentication, monitoring, and

auditing features to implement the required policies

• Infrastructure can be secured with moderately priced off-the-shelf HW and SW (firewalls, ACLs)

• Costs are primarily in initial configuration and support


Open Security Policies

• Policy might have simple or no passwords, unrestricted access to resources, and probably no monitoring and auditing

• Makes sense for a small company with the primary goal of making access to network resources easy

• Sensitive data, if it exists, might be kept on individual workstations that are backed up regularly and are physically inaccessible to other employees


Common Elements of Security Policies

• Virus protection for servers and desktop computers is a must

• There should be policies aimed at preventing viruses from being downloaded or spread

• Backup procedures for all data that can’t be easily reproduced should be in place, and a disaster recovery procedure must be devised

• Security is aimed not only at preventing improper use of or access to network resources, but also at safeguarding the company’s information


Securing Physical Access to the Network

• If there’s physical access to equipment, there is no security

– A computer left alone with a user logged on is particularly vulnerable

• If an administrator account is logged on, a person can even give his/her account administrator control

– If no user is logged on• People could log on to the computer with their own

accounts and access files to which they wouldn’t normally have access

• Computer could be restarted and booted from removable media, bypassing the normal OS security

• Computer or HDs could be stolen and later cracked


Physical Security Best Practices

• When planning your network, ensure that rooms are available to house servers and equipment– Rooms should have locks and be suitable for the

equipment being housed

• If a suitable room isn’t available, locking cabinets, freestanding or wall mounted, can be purchased to house servers and equipment in public areas

• Wiring from workstations to wiring cabinets should be inaccessible to eavesdropping equipment

• Physical security plan should include procedures for recovery from natural disasters (e.g., fire or flood)


Physical Security of Servers

• May be stashed away in lockable wiring closet

along with switch to which the server is connected

• Often require more tightly controlled environmental

conditions than patch panels, hubs, and switches

• Server rooms should be equipped with power

that’s preferably on a circuit separate from other

devices


Security of Internetworking Devices

• Routers and switches contain critical configuration information and perform essential network tasks– Internetworking devices, such as hubs, switches, and

routers, should be given as much attention in terms of physical security as servers

• A room with a lock is the best place for these devices

• Wall-mounted enclosure with a lock is second best– Some cabinets come with a built-in fan or have a

mounting hole for a fan

– They also come with convenient channels for wiring


Securing Access to Data

• Facets

– Authentication and authorization

– Encryption/decryption

– Virtual Private Networks (VPNs)

– Firewalls

– Virus and worm protection

– Spyware protection

– Wireless security


Secure Authentication and Authorization

• Administrators must control who has access to the network (authentication) and what users can do to the network (authorization)

– NOSs have tools to specify options and restrictions on how/when users can log on to network

• Password complexity requirements

• Logon hours

• Logon locations

• Remote logons, among others

– File system access controls and user permission settings


Configuring Password Requirements in a Windows

Environment

• Specify if passwords are required for all users,

how many characters a password must be, and

whether they should meet certain complexity

requirements

• XP allows passwords up to 128 characters

– Minimum of five to eight characters is typical

– If minimum length is 0, blank passwords are allowed

• Other options include Maximum/Minimum

password age, and Enforce password history

• When a user fails to enter a correct password, a

policy can be set to lock the user account


Configuring Password Requirements in a Windows

Environment


Configuring Password Requirements in a Linux

Environment

• Linux password configuration can be done

globally or on a user-by-user basis

• Options include maximum/minimum password

age, and number of days’ warning a user has

before password expires

– Linux system must be using shadow passwords, a

secure method of storing user passwords

– Options can be set by editing /etc/login.defs

• Use Pluggable Authentication Modules

(PAM) to set other options like account lockout,

password history, and complexity tests


Reviewing Password Dos and Don’ts

• Use a combination of uppercase letters, lowercase

letters, and numbers

• Include one or more special characters

• Try using a phrase, e.g., NetW@rk1ng !s C00l

• Don’t use passwords based on your logon name,

family members’ names, or even your pet’s name

• Don’t use common dictionary words unless they

are part of a phrase

• Don’t make your password so complex that you

forget it or need to write it down somewhere


Restricting Logon Hours and Logon Location


Authorizing Access to Files and Folders

• Windows OSs have two options for file security

– Sharing permissions are applied to folders (and only folders) shared over the network

• Don’t apply to files/folders if user is logged on locally

• These are the only file security options available in a FAT or FAT32 file system

– NTFS permissions allow administrators to assign permissions to files as well as folders

• Apply to file access by a locally logged-on user too

• Enable administrators to assign permissions to user accounts and group accounts

• Six standard permissions are available for folders


Securing Data with Encryption

• Use encryption to safeguard data as it

travels across the Internet and within the

company network

– Prevents somebody using eavesdropping

technology, such as a packet sniffer, from

capturing packets

• Data on disks can be secured with

encryption


Using IPSec to Secure Network Data

• The most popular method for encrypting

data as it travels network media is to use an

extension to the IP protocol called IP

Security (IPSec)

– Establishes an association between two

communicating devices

• Association is formed by two devices authenticating

their identities via a preshared key, Kerberos

authentication, or digital certificates

– After the communicating parties are

authenticated, encrypted communication can

commenceGuide to Networking Essentials, Fifth Edition 27

Securing Data on Disk Drives


Securing Communication with Virtual Private

Networks


VPNs in a Windows Environment

• Windows supports a special TCP/IP protocol called Point-to-Point Tunneling Protocol (PPTP)– A user running Windows can dial up a Windows server

when it’s running RRAS

– A VPN could be established permanently across the Internet by leasing dedicated lines at each end of a two-way link and maintaining ongoing PPTP-based communications across that dedicated link

• Starting with Windows 2000, Windows supports Layer 2 Tunneling Protocol (L2TP)– Supports advanced authentication and encryption

– Requires Windows machines on both sides


VPN Benefits

• Advantages of using VPNs– Installing several modems on an RRAS server so that

users can dial up the server directly isn’t necessary; instead, users can dial up any ISP

– Remote users can usually access an RRAS server by making only a local phone call, as long as they can access a local ISP

– When broadband Internet connectivity is available (e.g., DSL, cable modem), remote users can connect to the corporate network at high speed, making remote computing sessions more productive

• Additionally, VPNs save costs


Protecting Networks with Firewalls

• Firewall: HW device or SW program that

inspects packets going into or out of a network or

computer, and then discards/forwards them

based on rules

– Protects against outside attempts to access unauthorized

resources, and against malicious network packets

intended to disable or cripple a corporate network and its

resources

– If placed between Internet and corporate network, can

restrict users’ access to Internet resources

• Firewalls can attempt to determine the context of

a packet (stateful packet inspection (SPI))


Using a Router as a Firewall

• A firewall is just a router with specialized SW that

facilitates creating rules to permit or deny

packets

• Many routers have capabilities similar to firewalls

– After a router is configured, by default, all packets

are permitted both into and out of the network

– Network administrator must create rules (access

control lists) that deny certain types of packets

• Typically, an administrator builds access control lists so

that all packets are denied, and then creates rules that

make exceptions


Using Intrusion Detection Systems

• An IDS usually works with a firewall or router

with access control lists

– A firewall protects a network from potential break-ins

or DoS attacks, but an IDS must detect an attempted

security breach and notify the network administrator

– May be able to take countermeasures if an attack is in

progress

– Invaluable tool to help administrators know how often

their network is under attack and devise security

policies aimed at thwarting threats before they have a

chance to succeed


Using Network Address Translation to Improve

Security

• A benefit of NAT is that the real address of

an internal network resource is hidden and

inaccessible to the outside world

– Because most networks use NAT with private IP

addresses, those devices configured with

private addresses can’t be accessed directly

from outside the network

– An external device can’t initiate a network

conversation with an internal device, thus

limiting an attacker’s options to cause mischief


Protecting a Network from Worms, Viruses, and

Rootkits

• Malware is SW designed to cause harm/disruption to a computer system or perform activities on a computer without the consent of its owner– A virus spreads by replicating itself into other programs or

documents

– A worm is similar to a virus, but it doesn’t attach itself to another program

– A backdoor is a program installed on a computer that permits access to the computer, bypassing the normal authentication process

– To help prevent spread of malware, every computer should have virus-scanning software running


Protecting a Network from Worms, Viruses, and

Rootkits

• A Trojan program appears to be something

useful, but in reality contains some type of malware

• Rootkits are a form of Trojan programs that can

monitor traffic to and from a computer, monitor

keystrokes, and capture passwords

• The hoax virus is one of the worst kinds of viruses

– The flood of e-mail from people actually falling for the

hoax is the virus!

• Malware protection can be expensive; however,

the loss of data and productivity that can occur

when a network becomes infected is much more

costly


Protecting a Network from Spyware and Spam

• Spyware: monitors/controls part of a computer at the expense of user’s privacy and to the gain of a third party– Is not usually self-replicating

– Many anti-spyware programs are available, and some are bundled with popular antivirus programs

• Spam is simply unsolicited e-mail– Theft of e-mail storage space, network bandwidth, and

people’s time

– Detection and prevention is an uphill battle• For every rule or filter anti-spam software places on an e-mail

account, spammers find a way around them


Implementing Wireless Security

• Attackers who drive around looking for wireless

LANs to intercept are called wardrivers

• Wireless security methods

– Wired Equivalency Protocol (WEP)

– Wi-Fi Protected Access (WPA)

– MAC address filtering

• You should also set policies: limit AP signal

access, change encryption key regularly, etc.


Using a Cracker’s Tools to Stop Network Attacks

• If you want to design a good, solid network

infrastructure, hire a security consultant who

knows the tools of the cracker’s trade

– A cracker (black hat) is someone who attempts

to compromise a network or computer system for

the purposes of personal gain or to cause harm

– The term hacker has had a number of meanings

throughout the years

• White hats often use the term penetration tester for

their consulting services


Discovering Network Resources

• Attackers use command-line utilities such as

Ping, Traceroute, Finger, and Nslookup to

get information about the network

configuration and resources

– Other tools used• Ping scanner: automated method for pinging a range of IP

addresses

• Port scanner: determines which TCP and UDP ports are

available on a particular computer or device

• Protocol analyzers are also useful for resource discovery

because they allow you to capture packets and determine which

protocol’s services are running


Gaining Access to Network Resources

• One of the easiest resources to open is one in which no password is set– Check all devices that support Telnet, FTP, e-mail, and

Web services

– Verify that passwords are set on all devices and disable any unnecessary services

• If an attackers needs to learn user name/password:– Finger may be used to discover user names

– Linux, NetWare, and Windows servers have default administrator names that are often left unchanged

• Attacker may then use a password-cracking tool


Disabling Network Resources

• A denial-of-service (DoS) attack is an

attacker’s attempt to tie up network bandwidth

or network services so that it renders those

resources useless to legitimate users

– Packet storms typically use the UDP protocol

because it’s not connection oriented

– Half-open SYN attacks use TCP’s handshake to tie

up a server with invalid TCP sessions, thereby

preventing real sessions from being created

– In a ping flood, a program sends a large number of

ping packets to a host


Summary

• A network security policy describes rules governing

access to a company’s information resources– Should contain these types of policies: privacy policy, acceptable use

policy, authentication policy, Internet use policy, auditing policy, and

data protection policy

• Must secure physical access to network resources

• Securing access to data includes authentication and

authorization, encryption/decryption, VPNs,

firewalls, virus/worm/spyware protection, and

wireless security

• VPNs are an important aspect of network security– Secure remote access to private network (via Internet)


Summary

• Firewalls filter packets and permit or deny packets

based on a set of defined rules

• Malware can be viruses, worms, Trojans, and

rootkits

• Wireless security involves attention to configuring

SSID correctly and configuring/using wireless

security protocols, such as WEP, WPA, or 802.11i

• Tools that crackers use to compromise a network

can be used to determine whether a network is

secure

• DoS attacks are used to disrupt network operation


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