Security+ Guide to Network Security Fundamentals, Fourth Edition Chapter 6 Network Security

Security+ Guide to Network Security Fundamentals,

Fourth Edition

Chapter 6Network Security

Security+ Guide to Network Security Fundamentals, Fourth Edition

Objectives

• List the different types of network security devices and explain how they can be used

• Define network address translation and network access control

• Explain how to enhance security through network design

2

Security Through Network Devices

• Not all applications designed, written with security in mind– Network must provide protection

• Networks with weak security invite attackers

• Aspects of building a secure network– Network devices– Network technologies– Design of the network itself

Security+ Guide to Network Security Fundamentals, Fourth Edition 3

Standard Network Devices

• Security features found in network hardware– Provide basic level of security

• Open systems interconnection (OSI) model– Network devices classified based on function– Standards released in 1978, revised in 1983, still

used today– Illustrates:

• How network device prepares data for delivery

• How data is handled once received


Standard Network Devices (cont’d.)

• OSI model breaks networking steps into seven layers– Each layer has different networking tasks– Each layer cooperates with adjacent layers



Table 6-1 OSI reference model


• Hubs– Connect multiple Ethernet devices together:

• To function as a single network segment

– Use twisted-pair copper or fiber-optic cables– Work at Layer 1 of the OSI model– Do not read data passing through them– Ignorant of data source and destination– Rarely used today because of inherent security

vulnerability



• Switches– Network switch connects network segments– Operate at Data Link Layer (Layer 2)– Determine which device is connected to each port– Can forward frames sent to that specific device

• Or broadcast to all devices

– Use MAC address to identify devices– Provide better security than hubs



• Network administrator should be able to monitor network traffic– Helps identify and troubleshoot network problems

• Traffic monitoring methods– Port mirroring– Network tap (test access point)

• Separate device installed between two network devices



Figure 6-1 Port mirroring© Cengage Learning 2012


Figure 6-2 Network tap© Cengage Learning 2012


Table 6-2 Protecting the switch


• Routers– Forward packets across computer networks– Operate at Network Layer (Layer 3)– Can be set to filter out specific types of network

traffic

• Load balancers– Help evenly distribute work across a network– Allocate requests among multiple devices



• Advantages of load-balancing technology– Reduces probability of overloading a single server– Optimizes bandwidth of network computers– Reduces network downtime

• Load balancing is achieved through software or hardware device (load balancer)



• Security advantages of load balancing– Can stop attacks directed at a server or application– Can detect and prevent denial-of-service attacks– Some can deny attackers information about the

network• Hide HTTP error pages

• Remove server identification headers from HTTP responses


Network Security Hardware

• Specifically designed security hardware devices– Greater protection than standard networking devices

• Firewalls– Hardware-based network firewall inspects packets– Can either accept or deny packet entry– Usually located outside network security perimeter



Figure 6-3 Firewall location© Cengage Learning 2012

Network Security Hardware (cont’d.)

• Firewall actions on a packet– Allow (let packet pass through)– Block (drop packet)– Prompt (ask what action to take)

• Rule-based firewall settings– Set of individual instructions to control actions

• Settings-based firewall– Allows administrator to create parameters



Table 6-3 Rule for Web page transmission


• Methods of firewall packet filtering– Stateless packet filtering

• Inspects incoming packet and permits or denies based on conditions set by administrator

– Stateful packet filtering• Keeps record of state of connection

• Makes decisions based on connection and conditions



• Web application firewall– Looks deeply into packets that carry HTTP traffic

• Web browsers

• FTP

• Telnet

– Can block specific sites or specific known attacks– Can block XSS and SQL injection attacks



• Proxies– Devices that substitute for primary devices

• Proxy server– Computer or application that intercepts and

processes user requests– If a previous request has been fulfilled:

• Copy of the Web page may reside in proxy server’s cache

– If not, proxy server requests item from external Web server using its own IP address



Figure 6-4 Proxy server© Cengage Learning 2012


Figure 6-5 Configuring access to proxy servers© Cengage Learning 2012


• Proxy server advantages– Increased speed (requests served from the cache)– Reduced costs (cache reduces bandwidth required)– Improved management

• Block specific Web pages or sites

– Stronger security• Intercept malware

• Hide client system’s IP address from the open Internet



• Reverse proxy– Does not serve clients– Routes incoming requests to correct server– Reverse proxy’s IP address is visible to outside

users• Internal server’s IP address hidden



Figure 6-6 Reverse proxy© Cengage Learning 2012


• Spam filters– Enterprise-wide spam filters block spam before it

reaches the host

• Email systems use two protocols– Simple Mail Transfer Protocol (SMTP)

• Handles outgoing mail

– Post Office Protocol (POP)• Handles incoming mail



• Spam filters installed with the SMTP server– Filter configured to listen on port 25– Pass non-spam e-mail to SMTP server listening on

another port– Method prevents SMTP server from notifying

spammer of failed message delivery



Figure 6-7 Spam filter with SMTP server© Cengage Learning 2012


• Spam filters installed on the POP3 server– All spam must first pass through SMTP server and

be delivered to user’s mailbox– Can result in increased costs

• Storage, transmission, backup, deletion

• Third-party entity contracted to filter spam– All email directed to third-party’s remote spam filter– E-mail cleansed before being redirected to

organization



Figure 6-8 Spam filter on POP3 server© Cengage Learning 2012


• Virtual private network (VPN)– Uses unsecured network as if it were secure– All data transmitted between remote device and

network is encrypted

• Types of VPNs– Remote-access

• User to LAN connection

– Site-to-site• Multiple sites can connect to other sites over the

Internet



• Endpoints– Used in communicating VPN transmissions– May be software on local computer– May be VPN concentrator (hardware device)– May be integrated into another networking device

• VPNs can be software-based or hardware-based– Hardware-based generally have better security– Software-based have more flexibility in managing

network traffic



• Internet content filters– Monitor Internet traffic– Block access to preselected Web sites and files– Unapproved sites identified by URL or matching

keywords



Table 6-4 Internet content filter features


• Web security gateways– Can block malicious content in real time– Block content through application level filtering

• Examples of blocked Web traffic– ActiveX objects– Adware, spyware– Peer to peer file sharing– Script exploits



• Passive and active security can be used in a network– Active measures provide higher level of security

• Passive measures– Firewall– Internet content filter

• Intrusion detection system (IDS)– Active security measure– Can detect attack as it occurs



• Monitoring methodologies– Anomaly-based monitoring

• Compares current detected behavior with baseline

– Signature-based monitoring• Looks for well-known attack signature patterns

– Behavior-based monitoring• Detects abnormal actions by processes or programs

• Alerts user who decides whether to allow or block activity

– Heuristic monitoring• Uses experience-based techniques



Table 6-5 Methodology comparisons to trap port-scanning application


• Host intrusion detection system (HIDS)– Software-based application that can detect attack as

it occurs– Installed on each system needing protection– Monitors system calls and file system access– Can recognize unauthorized Registry modification– Monitors all input and output communications

• Detects anomalous activity



• Disadvantages of HIDS– Cannot monitor network traffic that does not reach

local system– All log data is stored locally– Resource-intensive and can slow system



• Network intrusion detection system (NIDS)– Watches for attacks on the network– NIDS sensors installed on firewalls and routers:

• Gather information and report back to central device

– Passive NIDS will sound an alarm– Active NIDS will sound alarm and take action

• Actions may include filtering out intruder’s IP address or terminating TCP session



Table 6-6 NIDS evaluation techniques


• Network intrusion prevention system (NIPS)– Similar to active NIDS– Monitors network traffic to immediately block a

malicious attack– NIPS sensors located in line on firewall itself



• All-in-one network security appliances– One integrated device replaces multiple security

devices

• Recent trend:– Combining multipurpose security appliances with

traditional device such as a router– Advantage of approach

• Network devices already process all packets

• Switch that contains anti-malware software can inspect all packets


Security Through Network Technologies

• Internet routers normally drop packet with a private address

• Network address translation (NAT)– Allows private IP addresses to be used on the public

Internet– Replaces private IP address with public address

• Port address translation (PAT)– Variation of NAT

• Outgoing packets given same IP address but different TCP port number



Table 6-7 Private IP addresses

Figure 6-9 Network address translation (NAT)© Cengage Learning 2012

Security Through Network Technologies (cont’d.)

• Advantages of NAT– Masks IP addresses of internal devices– Allows multiple devices to share smaller number of

public IP addresses

• Network access control– Examines current state of system or network device:

• Before allowing network connection

– Device must meet set of criteria• If not met, NAC allows connection to quarantine

network until deficiencies corrected



Figure 6-10 Network access control framework© Cengage Learning 2012

Security Through Network Design Elements

• Elements of a secure network design– Demilitarized zones– Subnetting– Virtual LANs– Remote access


Demilitarized Zone (DMZ)

• Separate network located outside secure network perimeter

• Untrusted outside users can access DMZ but not secure network



Figure 6-11 DMZ with one firewall© Cengage Learning 2012


Figure 6-12 DMZ with two firewalls© Cengage Learning 2012

Subnetting

• IP address may be split anywhere within its 32 bits

• Network can be divided into three parts– Network– Subnet– Host

• Each network can contain several subnets

• Each subnet can contain multiple hosts


Subnetting (cont’d.)

• Improves network security by isolating groups of hosts

• Allows administrators to hide internal network layout



Table 6-8 Advantages of subnetting


Figure 6-13 Subnets© Cengage Learning 2012

Virtual LANs (VLAN)

• Allow scattered users to be logically grouped together:– Even if attached to different switches

• Can isolate sensitive data to VLAN members

• Communication on a VLAN– If connected to same switch, switch handles packet

transfer– Special “tagging” protocol used for communicating

between switches


Remote Access

• Working away from the office commonplace today– Telecommuters– Traveling sales representatives– Traveling workers

• Strong security for remote workers must be maintained– Transmissions are routed through networks not

managed by the organization

• Provides same functionality as local users– Through VPN or dial-up connection


Summary

• Standard network security devices provide a degree of security– Hubs, switches, router, load balancer

• Hardware devices specifically designed for security give higher protection level– Hardware-based firewall, Web application firewall

• Proxy server intercepts and processes user requests

• Virtual private network uses unsecured public network and encryption to provide security


Summary (cont’d.)

• Intrusion detection system designed to detect attack as it occurs

• Network technologies can help secure a network– Network address translation– Network access control

• Methods for designing a secure network– Demilitarized zones– Virtual LANs


Documents

Security+ Guide to Network Security Fundamentals, Fourth Edition Chapter 6 Network Security