Infrastructure Security

Infrastructure security begins with the design of the infrastructure itself. The proper use of components improves not only performance but security as well. Network components are not isolated from the computing environment and are an essential aspect of a total computing environment. From the routers, switches, and cables that connect the devices, to the firewalls and gateways that manage communication, from the network design to the protocols employed, all of these items play essential roles in both performance and security.

In the CIA of security, the A for availability is often overlooked. Yet it is availability that has moved computing into this networked framework, and this concept has played a significant role in security. A failure in security can easily lead to a failure in availability and hence a failure of the system to meet user needs.

Security failures can occur in two ways. First, a failure can allow unauthorized users access to resources and data they are not authorized to use, compromising information security. Second, a failure can prevent a user from accessing resources and data the user is authorized to use. This second failure is often overlooked, but it can be as serious as the first. The primary goal of network infrastructure security is to allow all authorized use and deny all unauthorized use of resources.


A complete network computer solution in today's business environment consists of more than just client computers and servers. Devices are needed to connect the clients and servers and to regulate the traffic between them. Devices are also needed to expand this network beyond simple client computers and servers to include yet other devices, such as wireless and handheld systems. Devices come in many forms and with many functions, from hubs and switches, to routers, wireless access points, and special-purpose devices such as virtual private network (VPN) devices. Each device has a specific network function and plays a role in maintaining network infrastructure security.


Most users are familiar with the client computers used in the client/server model called workstation devices. The workstation is the machine that sits on the desktop and is used every day for sending and reading e-mail, creating spreadsheets, writing reports in a word processing program, and playing games. If a workstation is connected to a network, it is an important part of the security solution for the network. Many threats to information security can start at a workstation, but much can be done in a few simple steps to provide protection from many of these threats.

Workstations are attractive targets for crackers as they are numerous and can serve as entry points into the network and the data that is commonly the target of an attack. Although safety is a relative term, following these basic steps will increase workstation security immensely:

  • Remove unnecessary protocols such as Telnet, NetBIOS, IPX.

  • Remove modems unless needed and authorized.

  • Remove all shares that are not necessary.

  • Rename the administrator account, securing it with a strong password.

  • Remove unnecessary user accounts.

  • Install an antivirus program and keep abreast of updates.

  • If the floppy drive is not needed, remove or disconnect it.

  • Consider disabling USB ports via CMOS to restrict data movement to USB devices.

  • If no corporate firewall exists between the machine and the Internet, install a firewall.

  • Keep the operating system (OS) patched and up to date.

Antivirus Software for Workstations

Antivirus packages are available from a wide range of vendors. Running a network of computers without this basic level of protection will be an exercise in futility. Even though a virus attack is rare, the time and money you spend cleaning it up will more than equal the cost of antivirus protection. Even more important, once connected by networks, computers can spread a virus from machine to machine with an ease that's even greater than simple floppy disk transfer. One unprotected machine can lead to problems throughout a network as other machines have to use their antivirus software to attempt to clean up a spreading infection.

Even secure networks can fall prey to virus and worm contamination, and infection has been known to come from commercial packages. As important as antivirus software is, it is even more important to keep the virus definitions for the software up to date. Out-ofdate definitions can lead to a false sense of security, and many of the most potent virus and worm attacks are the newest ones being developed. The risk associated with a new virus is actually higher than for many of the old ones, which have been eradicated to a great extent by antivirus software.

A virus is a piece of software that must be introduced to the network and then executed on a machine. Workstations are the primary mode of entry for a virus into a network. Although a lot of methods can be used to introduce a virus to a network, the two most common are transfer of an infected file from another networked machine and from email. A lot of work has gone into software to clean e-mail while in transit and at the mail server. But transferred files are a different matter altogether. People bring files from home, from friends, from places unknown and then execute them on a PC for a variety of purposes. It doesn't matter whether it is a funny executable, a game, or even an authorized work application-the virus doesn't care what the original file is, it just uses it to gain access. Even sharing of legitimate work files and applications can introduce viruses.

Once considered by many users to be immune, Apple Macintosh computers had very few examples of malicious software in the wild. This was not due to anything other than a low market share, and hence the devices were ignored by the malware community as a whole. As Mac has increased in market share, so has its exposure, and today a variety of Mac OS X malware steals files and passwords and is even used to take users' pictures with the computer's built-in webcam. All user machines need to install antivirus software in today's environment, because any computer can become a target.

Additional Precautions for Workstations

Personal firewalls are a necessity if a machine has an unprotected interface to the Internet. These are seen less often in commercial networks, as it is more cost effective to connect through a firewall server. With the advent of broadband connections for homes and small offices, this needed device is frequently missed. This can result in penetration of a PC from an outside hacker or a worm infection. Worst of all, the workstation can become part of a larger attack against another network, unknowingly joining forces with other compromised machines in a distributed denial-of-service (DDoS) attack.


Servers are the computers in a network that host applications and data for everyone to share. Servers come in many sizes, from small single-CPU boxes that can be less powerful than a workstation, to multiple-CPU monsters, up to and including mainframes. The operating systems used by servers range from Windows Server, to Linux/UNIX, to Multiple Virtual Storage (MVS) and other mainframe operating systems. The OS on a server tends to be more robust than the OS on a workstation system and is designed to service multiple users over a network at the same time. Servers can host a variety of applications, including web servers, databases, e-mail servers, file servers, print servers, and application servers for middleware applications.

The key management issue behind running a secure server setup is to identify the specific needs of a server for its proper operation and enable only items necessary for those functions. Keeping all other services and users off the system improves system throughput and increases security. Reducing the attack surface area associated with a server reduces the vulnerabilities now and in the future as updates are required.

Once a server has been built and is ready to place into operation, the recording of MD5 hash values on all of its crucial files will provide valuable information later in case of a question concerning possible system integrity after a detected intrusion. The use of hash values to detect changes was first developed by Gene Kim and Eugene Spafford at Purdue University in 1992. The concept became the product Tripwire, which is now available in commercial and open source forms. The same basic concept is used by many security packages to detect file level changes.

Antivirus Software for Servers

The need for antivirus protection on servers depends a great deal on the use of the server. Some types of servers, such as e-mail servers, can require extensive antivirus protection because of the services they provide. Other servers (domain controllers and remote access servers, for example) may not require any antivirus software, as they do not allow users to place files on them. File servers will need protection, as will certain types of application servers. There is no general rule, so each server and its role in the network will need to be examined for applicability of antivirus software.

Network Interface Cards

To connect a server or workstation to a network, a device known as a network interface card (NIC) is used. A NIC is a card with a connector port for a particular type of network connection, either Ethernet or Token Ring. The most common network type in use for local area networks is the Ethernet protocol, and the most common connector is the RJ-45 connector. Figure 8-1 shows a RJ-45 connector (lower) compared to a standard telephone connector (upper). Additional types of connectors include coaxial cable connectors, frequently used with cable modems and extending from the wall to the cable modem.

The purpose of a NIC is to provide lower level protocol functionality from the OSI (Open System Interconnection) model. A NIC is the physical connection between a computer and the network. As the NIC defines the type of physical layer connection, different NICs are used for different physical protocols. NICs come as single-port and multiport, and most workstations use only a single-port NIC, as only a single network connection is needed. For servers, multiport NICs are used to increase the number of network connections, increasing the data throughput to and from the network.


Hubs are networking equipment that connects devices using the same protocol at the physical layer of the OSI model. A hub allows multiple machines in an area to be connected together in a star configuration with the hub as the center. This configuration can save significant amounts of cable and is an efficient method of configuring an Ethernet backbone. All connections on a hub share a single collision domain, a small cluster in a network where collisions occur. As network traffic increases, it can become limited by collisions. The collision issue has made hubs obsolete in newer, higher

performance networks, with low-cost switches and switched Ethernet keeping costs low and usable bandwidth high. Hubs also create a security weakness in that all connected devices see all traffic, enabling sniffing and eavesdropping to occur.

Bridges are networking equipment that connects devices using the same protocol at the physical layer of the OSI model. A bridge operates at the data link layer, filtering traffic based on MAC addresses. Bridges can reduce collisions by separating pieces of a network into two separate collision domains, but this only cuts the collision problem in half. Although bridges are useful, a better solution is to use switches for network connections.


Switches form the basis for connections in most Ethernet-based local area networks (LANs). Although hubs and bridges still exist, in today's high-performance network environment switches have replaced both. A switch has separate collision domains for each port. This means that for each port, two collision domains exist: one from the port to the client on the downstream side and one from the switch to the network upstream.


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When full duplex is employed, collisions are virtually eliminated from the two nodes, host and client. This also acts as a security factor in that a sniffer can see only limited traffic, as opposed to a hub-based system, where a single sniffer can see all of the traffic to and from connected devices.

Switches operate at the data link layer, while routers act at the network layer. For intranets, switches have become what routers are on the Internet-the device of choice for connecting machines. As

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switches have become the primary network connectivity device, additional functionality has been added to them. A switch is usually a layer 2 device, but layer 3 switches incorporate routing functionality.

Switches can also perform a variety of security functions. Switches work by moving packets from inbound connections to outbound connections. While moving the packets, it is possible to inspect the packet headers and enforce security policies. Port address security based on MAC addresses can determine whether a packet is allowed or blocked from a connection. This is the very function that a firewall uses for its determination, and this same functionality is what allows an 802.1x device to act as an "edge device."

Virtual Local Area Networks

The other security feature that can be enabled in some switches is the concept of virtual local area networks (VLANs). Cisco defines a VLAN as a "broadcast domain within a switched network," meaning that information is carried in broadcast mode only to devices within a VLAN. Switches that allow multiple VLANs to be defined enable broadcast messages to be segregated into the specific VLANs. If each floor of an office, for example, were to have a single switch and you had accounting functions on two floors, engineering functions on two floors, and sales functions on two floors, then separate VLANs for accounting, engineering, and sales would allow separate broadcast domains for each of these groups, even those that spanned floors. This configuration increases network segregation, increasing throughput and security.

Unused switch ports can be preconfigured into empty VLANs that do not connect to the rest of the network. This significantly increases security against unauthorized network connections. If, for example, a building is wired with network connections in all rooms, including multiple connections for convenience and future expansion, these unused ports become open to the network.

One solution is to disconnect the connection at the switch, but this merely moves the network opening into the switch room.

The better solution is to disconnect it and disable the port in the switch. This can be accomplished by connecting all unused ports into a VLAN that isolates them from the rest of the network.


Routers are network traffic management devices used to connect different network segments together.

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Routers operate at the network layer of the OSI model, routing traffic using the network address (typically an IP address) utilizing routing protocols to determine optimal routing paths across a network. Routers form the backbone of the Internet, moving traffic from network to network, inspecting packets from every communication as they move traffic in optimal paths.

Routers operate by examining each packet, looking at the destination address, and using algorithms and tables to determine where to send the packet next. This process of examining the header to determine the next hop can be done in quick fashion. Routers use access control lists (ACLs) as a method of deciding whether a packet is allowed to enter the network. With ACLs, it is also possible to examine the source address and determine whether or not to allow a packet to pass. This allows routers equipped with ACLs to drop packets according to rules built in the ACLs. This can be a cumbersome process to set up and maintain, and as the ACL grows in size, routing efficiency can be decreased. It is also possible to configure some routers to act as quasi-application gateways, performing stateful packet inspection and using contents as well as IP addresses to determine whether or not to permit a packet to pass. This can tremendously increase the time for a router to pass traffic and can significantly decrease router throughput.


A firewall can be hardware, software, or a combination whose purpose is to enforce a set of network security policies across network connections. It is much like a wall with a window: the wall serves to keep things out, except those permitted through the window. Network security policies act like the glass in the window; they permit some things to pass, such as light, while blocking others, such as air. The heart of a firewall is the set of security policies that it enforces. Management determines what is allowed in the form of network traffic between devices, and these policies are used to build rule sets for the firewall devices used to filter network traffic across the network.

Security policies are rules that define what traffic is permissible and what traffic is to be blocked or denied. These are not universal rules, and many different sets of rules are created for a single company with multiple connections. A web server connected to the Internet may be configured to allow traffic only on port 80 for HTTP and have all other ports blocked, for example. An e-mail server may have only necessary ports for e-mail open, with others blocked. The network firewall can be programmed to block all traffic to the web server except for port 80 traffic, and to block all traffic bound to the mail server except for port 25. In this fashion, the firewall acts as a security filter, enabling control over network traffic, by machine, by port, and in some cases based on application level detail. A key to setting security policies for firewalls is the same as has been seen for other security policies-the principle of least access. Allow only the necessary access for a function; block or deny all unneeded functionality. How a firm deploys its firewalls determines what is needed for security policies for each firewall.

How Do Firewalls Work?

Firewalls enforce the established security policies through a variety of mechanisms, including the following:

  • Network Address Translation (NAT)

  • Basic packet filtering

  • Stateful packet filtering

  • ACLs

  • Application layer proxies

One of the most basic security functions provided by a firewall is NAT, which allows you to mask significant amounts of information from outside of the network. This allows an outside entity to communicate with an entity inside the firewall without truly knowing its address. NAT is a technique used in IPv4 to link private IP addresses to public ones. Private IP addresses are sets of IP addresses that can be used by anyone and by definition are not routable across the Internet. NAT can assist in security by preventing direct access to devices from outside the firm, without first having the address changed at a NAT device. The benefit is less public IP addresses are needed, and from a security point of view the internal address structure is not known to the outside world. If a hacker attacks the source address, he is simply attacking the NAT device, not the actual sender of the packet.

NAT was conceived to resolve an address shortage associated with IPv4 and is considered by many to be unnecessary for IPv6. The added security features of enforcing traffic translation and hiding internal network details from direct outside connections will give NAT life well into the IPv6 timeframe.

Basic packet filtering, the next most common firewall technique, involves looking at packets, their ports, protocols, source and destination addresses, and checking that information against the rules configured on the firewall. Telnet and FTP connections may be prohibited from being established to a mail or database server, but they may be allowed for the respective service servers. This is a fairly simple method of filtering based on information in each packet header, such as IP addresses and TCP/UDP ports. Packet filtering will not detect and catch all undesired packets, but it is fast and efficient.


Wireless devices bring additional security concerns. There is, by definition, no physical connection to a wireless device; radio waves or infrared carry data, which allows anyone within range access to the data. This means that unless you take specific precautions, you have no control over who can see your data. Placing a wireless device behind a firewall does not do any good, because the firewall stops only physically connected traffic from reaching the device. Outside traffic can come literally from the parking lot directly to the wireless device.

The point of entry from a wireless device to a wired network is performed at a device called a wireless access point. Wireless access points can support multiple concurrent devices accessing network resources through the network node they provide.

Several mechanisms can be used to add wireless functionality to a machine. For PCs, this can be done via an expansion card. For notebooks, a PCMCIA adapter for wireless networks is available from several vendors. For both PCs and notebooks, vendors have introduced USB-based wireless connectors.


Modems were once a slow method of remote connection that was used to connect client workstations to remote services over standard telephone lines. Modem is a shortened form of modulator/demodulator, covering the functions actually performed by the device as it converts analog signals to digital and vice versa. To connect a digital computer signal to the analog telephone line required one of these devices. Today, the use of the term has expanded to cover devices connected to special digital telephone lines-DSL modems-and to cable television lines-cable modems. Although these devices are not actually modems in the true sense of the word, the term has stuck through marketing efforts directed to consumers. DSL and cable modems offer broadband high-speed connections and the opportunity for continuous connections to the Internet. Along with these new desirable characteristics come some undesirable ones, however. Although they both provide the same type of service, cable and DSL modems have some differences. A DSL modem provides a direct connection between a subscriber's computer and an Internet connection at the local telephone company's switching station.

This private connection offers a degree of security, as it does not involve others sharing the circuit. Cable modems are set up in shared arrangements that theoretically could allow a neighbor to sniff a user's cable modem traffic. Both cable and DSL services are designed for a continuous connection, which brings up the question of IP address life for a client. Although some services originally used a static IP arrangement, virtually all have now adopted the Dynamic Host Configuration Protocol (DHCP) to manage their address space. A static IP has an advantage of being the same and enabling convenient DNS connections for outside users. As cable and DSL services are primarily designed for client services as opposed to host services, this is not a relevant issue. A

security issue of a static IP is that it is a stationary target for hackers. The move to DHCP has not significantly lessened this threat, however, for the typical IP lease on a cable modem DHCP is for days. This is still relatively stationary, and some form of firewall protection needs to be employed by the user.

Cable/DSL Security

The modem equipment provided by the subscription service converts the cable or DSL signal into a standard Ethernet signal that can then be connected to a NIC on the client device. This is still just a direct network connection, with no security device separating the two. The most common security device used in cable/DSL connections is a firewall. The firewall needs to be installed between the cable/DSL modem and client computers.


Private branch exchanges (PBXs) are an extension of the public telephone network into a business. Although typically considered a separate entity from data systems, they are frequently interconnected and have security requirements as part of this interconnection as well as of their own. PBXs are computer-based switching equipment designed to connect telephones into the local phone system. Basically digital switching systems, they can be compromised from the outside and used by phone hackers (phreakers) to make phone calls at the business' expense. Although this type of hacking has decreased with lower cost long distance, it has not gone away, and as several firms learn every year, voice mail boxes and PBXs can be compromised and the long-distance bills can get very high, very fast.

Another problem with PBXs arises when they are interconnected to the data systems, either by corporate connection or by rogue modems in the hands of users. In either case, a path exists for connection to outside data networks and the Internet. Just as a firewall is needed for security on data connections, one is needed for these connections as well. Telecommunications firewalls are a distinct type of firewall designed to protect both the PBX and the data connections. The functionality of a telecommunications firewall is the same as that of a data firewall: it is there to enforce security policies.

Telecommunication security policies can be enforced even to cover hours of phone use to prevent unauthorized long-distance usage through the implementation of access codes and/or restricted service hours.


Remote Access Service (RAS) is a portion of the Windows OS that allows the connection between a client and a server via a dial-up telephone connection. Although slower than cable/DSL connections, this is still a common method for connecting to a remote network. When a user dials into the computer system, authentication and authorization are performed through a series of remote access protocols. For even greater security, a callback system can be employed, where the server calls back to the client at a set telephone number for the data exchange. RAS can also mean Remote Access Server, a term for a server designed to permit remote users access to a network and to regulate their access. A variety of protocols and methods exist to perform this function.


A virtual private network (VPN) is a construct used to provide a secure communication channel between users across public networks such as the Internet. A variety of techniques can be employed to instantiate a VPN connection.

The use of encryption technologies allows either the data in a packet to be encrypted or the entire packet to be encrypted. If the data is encrypted, the packet header can still be sniffed and observed between source and destination, but the encryption protects the contents of the packet from inspection. If the entire packet is encrypted, it is then placed into another packet and sent via tunnel across the public network. Tunneling can protect even the identity of the communicating parties.

The most common implementation of VPN is via IPsec, a protocol for IP security. IPsec is mandated in IPv6 and is optionally back-fitted into IPv4. IPsec can be implemented in hardware, software, or a combination of both.

Intrusion Detection Systems

Intrusion detection systems (IDSs) are designed to detect, log, and respond to unauthorized network or host use, both in real time and after the fact. IDSs are available from a wide selection of vendors and are an essential part of network security. These systems are implemented in software, but in large systems, dedicated hardware is required as well. IDSs can be divided into two categories: network-based systems and host-based systems. Two primary methods of detection are used: signature-based and anomaly-based.

Network Access Control

Networks comprise connected workstations and servers. Managing security on a network involves managing a wide range of issues, from various connected hardware and the software operating these devices. Assuming that the network is secure, each additional connection involves risk. Managing the endpoints on a case-by-case basis as they connect is a security methodology known as network access control. Two main competing methodologies exist: Network Access Protection (NAP) is a Microsoft technology for controlling network access of a computer host, and Network Admission Control (NAC) is Cisco's technology for controlling network admission.

Both the Cisco NAC and Microsoft NAP are in their early stages of implementation. The concept of automated admission checking based on client device characteristics is here to stay, as it provides timely control in the ever-changing network world of today's enterprises.

Network Monitoring/Diagnostic

The computer network itself can be considered a large computer system, with performance and operating issues. Just as a computer needs management, monitoring, and fault resolution, so do networks. SNMP was developed to perform this function across networks. The idea is to enable a central monitoring and control center to maintain, configure, and repair network devices, such as switches and routers, as well as other network services such as firewalls, IDSs, and remote access servers. SNMP has some security limitations, and many vendors have developed software solutions that sit on top of SNMP to provide better security and better management tool suites.

The concept of a network operations center (NOC) comes from the old phone company network days, when central monitoring centers monitored the health of the telephone network and provided interfaces for maintenance and management. This same concept works well with computer networks, and companies with midsize and larger networks employ the same philosophy. The NOC allows operators to observe and interact with the network, using the self-reporting and in some cases self-healing nature of network devices to ensure efficient network operation. Although generally a boring operation under normal conditions, when things start to go wrong, as in the case of a virus or worm attack, the center can become a busy and stressful place as operators attempt to return the system to full efficiency while not interrupting existing traffic.

As networks can be spread out literally around the world, it is not feasible to have a person visit each device for control functions. Software enables controllers at NOCs to measure the actual performance of network devices and make changes to the configuration and operation of devices remotely. The ability to make remote connections with this level of functionality is both a blessing and a security issue. Although this allows efficient network operations management, it also provides an opportunity for unauthorized entry into a network. For this reason, a variety of security controls are used, from secondary networks to VPNs and advanced authentication methods with respect to network control connections.

Mobile Devices

Mobile devices such as personal digital assistants (PDAs) and mobile phones are the latest devices to join the corporate network. These devices can perform significant business functions, and in the future, more of them will enter the corporate network and more work will be performed with them. These devices add several challenges for network administrators. When they synchronize their data with that on a workstation or server, the opportunity exists for viruses and malicious code to be introduced to the network. This can be a major security gap, as a user may access separate e-mail accounts, one personal, without antivirus protection, the other corporate. Whenever data is moved from one network to another via the PDA, the opportunity to load a virus onto the workstation exists. Although the virus may not affect the PDA or phone, these devices can act as transmission vectors. Currently, at least one vendor offers antivirus protection for PDAs, and similar protection for phones is not far away.