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Learn how to develop a network security policy that balances accessibility with the need for security. Understand threats to network security and implement measures to protect your network. Apply patches and upgrades, and use firewalls to enhance security.
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Chapter 14Network Security 14.1 - Developing a Network Security Policy 14.2 - Threats to Network Security 14.3 - Implementing Security Measures 14.4 - Appling Patches and Upgrades 14.5 - Firewalls
Accessing Security Needs • There must always be a delicate balance between security and accessibility. • The more accessible a network is, the less secure it is. • When it comes to a computer network, how much security is enough? • There are several factors to consider: • The type of business in which the company engages • The type of data stored on the network • The management philosophy of the organization
Acceptable Use Policy • The first step in creating a security policy for a company network is to define an Acceptable Use Policy (AUP). • An AUP tells the users what is acceptable and allowed on the company network. • To view some examples of AUPs, visit these websites:
Username and Password Standards • Usually the system administrator will define the naming convention for the usernames on a network. • A common example is the first initial of the person's first name and then the entire last name. • A complex username naming convention is not as important as having a complex password standard. • When assigning passwords, the level of password control should match the level of protection required.
Rules for Network Access • A system administrator who assigns the proper permissions on the share drives and directories defines the rules for network access. • By assigning the proper security permissions on the network, the system administrator should know who has access to specific directories. • Proper maintenance by the system administrator will be required to examine auditing logs of attempts that have been made to access the network shares.
Policy for Disposal of Materials • Hardware, software, and data should never just be thrown away. • There are strict regulations that should be followed to control the disposal of computer components. • The system administrator is responsible for developing a policy based on environmental and safety guidelines for hardware that no longer works. • To view some examples of the disposal of materials policies visit these websites:
Virus Protection Standards • Place proper filters and access lists on all the incoming gateways to protect the network from unwanted access. • To prevent viruses, e-mail policies also need to be developed that state what may be sent and received. • These websites provide sample e-mail policy standards:
Online Security Resources • Web-based resources offer critical information and powerful tools that can be used to protect a network. Some of the best online security resources are the NOS manufacturer websites • To view examples of the online security resources visit these websites:
Server Room Security • To protect computing resources, make sure that there is a locked door and four walls between the server and the rest of the area. • There are a variety of ways to permit or deny access to that area after it has been secured. • The lock and key is a tried and true method for physically securing the server environment. • This method works great if there are a limited number of people who need access.
Server Room Security • Using a combination locking mechanism is similar to a lock and key. The advantages to this method: • Keys no longer have to be distributed • Key control lists no longer have to be maintained • Combinations can also be reset when needed • The one drawback to this model is that it is very easy to share a combination with someone not authorized. • Card readers are the most common of the access control mechanisms. • They work by reading a magnetic signature off an access card or token. • A biometrics based access control system uses measurable physical characteristics to authenticate users into an environment (fingerprints, retinal patterns, or speech).
Anti-Theft Devices for Server Hardware • A common security measures is the locking mechanism included as part of the server itself. • Most high end servers enable the case to be locked, and in many cases to lock the drives into the server chassis. • Almost all rack systems include locking front and back doors. • Removable media drive locksare locking devices. • These devices fit over the floppy drive, zip drive, and CD-ROM drive to prevent unauthorized access. • Some servers are shipped with holes in the cases, which are predrilled for a padlock. • Alarms are the final add-on, and best suited for the shared office environment.
Securing Removable Media • Security of removable media includes the following: • Removable disks, floppy, Zip, Jaz, LS120, CD-RW • Removable hard drives • Backup media, tapes • Several methods are used to ensure the security of removable media: • Lock the media in an office • Place the media in a locked cabinet with strict key control • Place the media in a safe, or a fire-resistant safe • Engage a third-party firm to store the tapes in their secure facility
Overview: Internal/External Security • The Internet essentially works by following rules that are open to the public. • If one studies the rules enough, one is bound to find loopholes and weaknesses that can be exploited. • The number of individuals, organizations, and institutions connected to the Internet are growing. • Connecting to the Internet opens the door to network intruders.
Outside Threats • Several outside sources can cause attacks: • Hackers - the true hacker desires to dissect systems and programs to see how they work. • Crackers - those that break in to computer systems to tamper with, steal, or destroy data. • Virus - it causes some unexpected and usually undesirable event. • Worms - a self-replicating virus that does not alter files but resides in active memory and duplicates itself. • Trojan horse - is a program that presents itself as another program to obtain information
Denial of Service (DoS) • A DoS attack occurs when the targeted system cannot service legitimate network requests effectively. • As a result, the system has become overloaded by illegitimate messages. • DoS attacks originate from one host or a group of hosts. • When the attack comes from a coordinated group of hosts, such attacks are called Distributed DoS (DDoS). • A common DoS attack is to overload a target system by sending more data than it can handle.
Denial of Service (DoS) • There are several specific types of DoS attacks: • A buffer overflow attack is designed to overwhelm the software running on the target system. • The so-called ping of death is a well known buffer overflow DoS attack. • The TCP synchronization (SYN) attack exploits the TCP protocol three-way handshake. • The attacker sends a large volume of TCP synchronization requests (SYN requests).
Distributed Denial of Service (DDoS) • Before the hacker can attack the ultimate target, a "fleet" of "zombies" (unsecure host with a permanent Internet connection) must be coordinated for the attack. • The hacker takes advantage of the zombie's lack of security. • The hacker breaks in to the system either directly or through an e-mail virus. • The goal of the break in or virus is to install software on the zombie system. • The hacker uses the zombies to launch a DDoS attack on the ultimate target.
Well Known Exploits • Each combination of NOS and application software contains it’s own unique set of vulnerabilities and weaknesses. • Threats to network security comes from individuals with sophisticated tools. • Some of these individuals are often called "script kiddies". • Script kiddy is a negative term used to describe immature individuals that use scripts, software programs, or techniques created by other, more skilled crackers.
Trojan Horse Programs • A Trojan horse is a program that presents itself as another program to obtain information. For example, there is a Trojan horse that emulates the system login screen. • When users type in their account name and password, the information is stored or transmitted to the originator of the Trojan horse. The username and password can then be used to gain access to the system.
Inside Threats • Corporate espionage is the most sophisticated type of internal security threat. • Employees can be approached by competing companies. • There are freelance corporate spies who take assignments on a contract basis. • Internal security breaches can also be the result of rebellious users who disagree with security policies. • While not accidental, these breaches are not designed to cause harm.
File Encryption • File encryption is a way of encrypting data stored on a computer disk so that it is unreadable to anyone but the creator of the data. • Windows 2000 includes a file encryption function. • Windows 9x and Windows NT do not. • Third party encryption programs are available for OSs: • PC Guardian, Deltacrypt, Winzap
IP Security • IPSec secures data at the packet level. • It works at the network layer of the OSI model. • The Authentication Header (AH) enables verification of the sender identity. • Encapsulating Security Payload (ESP) ensures the confidentiality of the data itself. • IPSec can operate in either the transport mode or the tunnel mode.
Secure Sockets Layer (SSL) • SSL was developed by Netscape to provide security for its web browser. • It uses public and private key encryption. • SSL operates at the application layer and must be supported by the user application.
E-mail Security • E-mail users think they have the same expectation of privacy when sending e-mail as they do when sending a letter through the postal service. • A more accurate expectation would be to assume that the e-mail is like a postcard that can be read by anyone who handles it during its journey from sender to recipient. • They often travel through dozens of nodes or servers on their way from sender to recipient.
Public/Private Key Encryption • One key is published and is widely available. • The other key is private and known only to the user. • Both keys are required to complete the secure communication. • This type of encryption, is also referred to as asymmetric encryption. • With this type of encryption, each user has both a public and a private key, called a key pair.
Finding Patches and Upgrades • Patches are fixes to existing software code. • A NOS manufacturer typically provides security patches. • Microsoft now includes the option to use software called Windows Update with its operating systems.
Selecting Patches and Upgrades • Software makers recommend installing software security patches immediately. • This is done to reduce exposure to known vulnerabilities. • Software venders release security updates as soon as they are available. • Understanding the effect on the system will help determine if an update, fix, or patch is necessary.
Applying Patches and Upgrades • Periodically, NOS vendors issue updates to their network operating systems. These updates have various names: • Microsoft Service Packs • IBM Fixpacs • Novell Patches • These updates usually fix bugs or close security holes that have been found in the released version of the OS. • Download the updates from the network operating system vendor’s website.
Introduction to Firewalls and Proxies • A proxy is software that interacts with outside networks on behalf of a client host. • Typically, client hosts on a secure LAN request a web page from a server running proxy services. • The proxy server then goes out on the Internet to retrieve the web page. • The web page is then copied to the proxy server, this is referred to as caching.
Introduction to Firewalls and Proxies • Administrators use NetworkAddress Translation (NAT) to alter the source address of packets originating from a secure LAN. • This allows secure LANs to be addressed using private IP addresses. • Private IP addresses are not routed on the Internet. • An outside hacker cannot directly reach a computer with a private address. • Some experts make a distinction between NAT and a firewall. Others look at NAT as part of a comprehensive firewall solution.
Packet Filtering • The most basic firewall solution is an IP packet filter. • To configure a packet filter, a network administrator must define the rules that describe how to handle specified packets. • The most basic firewall solution is an IP packet filter. • To configure a packet filter, a network administrator must define the rules that describe how to handle specified packets.
Packet Filtering • Both TCP and UDP use port numbers to address specific applications running on a host. • Both TCP and UDP use port numbers to address specific applications running on a host. • Firewall software must guess at what connectionless traffic is invited and what connectionless traffic is not. • The most comprehensive form of packet filtering examines layer 3 and 4 headers and the layer 7 application data as well. • Layer 7 firewalls look for patterns in the payload of the packet. • This is done in an effort to determine what application is being used, such as HTTP, FTP, and so on.
Firewall Placement • A boundary router connects the enterprise LAN to its ISP or the Internet. • The boundary router should only allow HTTP, FTP, mail, and DNS related traffic to the DMZ. • The DMZ is designed to keep the inside network clean. • The NOS servers in the DMZ should be tightly configured.
Common Firewall Solutions • The PIX Firewall 515 uses TFTP for image download and upgrade. • It has a low profile design, 128,000 simultaneous sessions, and 170 Mbps thru-put. • The PIX Firewall 520 uses a 3.5-inch floppy disk drive to load the image and upgrade. • It has an enterprise chassis design, 256,000 simultaneous sessions, and 240 Mbps thru-put. • The PIX Firewall is secure right out of the box. • Default settings allow all connections from the inside interface access to the outside interface.
Common Firewall Solutions • The Cisco IOS Firewall Feature Set provides stateful packet filtering. • Another firewall solution is a UNIX host. • The UNIX host serves as a router, running packet filtering software such as ipfw, and/or NAT. • Home users have a variety of firewall options available as well.
Using an NOS as a Firewall • In high-traffic environments, a specialized packet filtering and NAT solution is recommended. • A device such as a router or firewall appliance is designed to switch packets and manipulate them quickly. • A NOS running on ordinary hardware may be able to do the job. • However, it is not without adding latency and overhead on the server. • In low traffic environments, such as small offices and home networks, a NOS firewall solution is a good choice.
