Network connectivity can be both a blessing and a curse. On the one hand, network connectivity can enable users to share files, exchange e-mail, and pool physical resources. Yet network connectivity can also be a risky endeavor, if the connectivity grants access to would-be intruders. The Internet is a perfect case in point. Designed for a trusted environment, many contemporary exploits are based upon vulnerabilities inherent to the protocol itself. In light of this trend, many organizations are implementing firewalls to protect their internal network from the untrusted Internet.firewall, network connection, risks, vulnerabilities

Radu Constantinescu

English

Research Papers in Economics

Firewall Management 
 
Prep. drd. Radu Constantinescu 
Academy of Economics Studies, Bucharest 
 
ABSTRACT 
Network connectivity can be both a blessing and a curse. On the one hand, network connectivity can 
enable users to share files, exchange e-mail, and pool physical resources. Yet network connectivity can 
also be a risky endeavor, if the connectivity grants access to would-be intruders. The Internet is a perfect 
case in point. Designed for a trusted environment, many contemporary exploits are based upon 
vulnerabilities inherent to the protocol itself. In light of this trend, many organizations are implementing 
firewalls to protect their internal network from the untrusted Internet. 
 
1. Introduction 
 
Obtaining management support for a firewall prior to implementation can be very useful after the firewall 
is implemented. When a firewall is implemented on a network for the first time, it will almost surely be 
the source of many complaints. For example: 
•  Organizations that have never before had firewalls almost never have the kind of 
documentation necessary to support user requirements. 
•  If the firewall hides information about the internal network from the outside network, this 
will break any network transactions in which the remote system uses an access control list, and the 
address of the firewall is not included in that list. 
•  Certain types of message traffic useful in network troubleshooting (e.g., PING, 
TRACEROUTE) may no longer work. 
 
All of these problems can be solved, but the point is that coordination with senior management prior to 
installation can make life much easier for firewall administrators. 
 
2. Firewalls and the Local Security Policy 
 
A firewall can be defined as a system with the following set of characteristics: 
•  All traffic between the two networks must pass through the firewall. 
•  Only traffic that is authorized by the local security policy will be allowed to pass. 
•  The firewall itself is immune to penetration.  
 
Like any security tool, a firewall merely provides the capability to increase the security of the path 
between two networks. It is the responsibility of the firewall administrator to take advantage of this 
capability; and no firewall can guarantee absolute protection from outside attacks. The risk analysis 
should define the level of protection that can be expected from the firewall; the local security policy 
should provide general guidelines on how this protection will be achieved; and both the assessment and 
revised policy should be accepted by top management prior to firewall implementation. 
Despite the fact that, according to (1), all traffic between the two networks must pass through the firewall, 
in practice this is not always technically feasible or convenient. Network administrators supporting legacy 
or proprietary systems may find that getting them to communicate through the firewall may not be as easy 
as firewall vendors claim, if even possible. And even if there are no technical obstacles to routing all 
traffic through the firewall, users may still complain that the firewall is inconvenient or slows down their systems. Thus, the local security policy should specify the process by which requests for exceptions (1) 
will be considered. 
As (2) states, the local security policy defines what the firewall is supposed to enforce. If a firewall is 
going to allow only "authorized" traffic between two networks, then the firewall has to know what traffic 
is "authorized." The local security policy should define "authorized" traffic, and it should do so at a 
somewhat technical level. The policy should also state a default rule for evaluating requests: either all 
traffic is denied except that which is specifically authorized, or all traffic is allowed except that which is 
specifically denied. 
Network devices which protect other network devices should themselves be protected against intruders. If 
the protection device were not secure, intruders could compromise the device and then compromise the 
system that the device was supposed to protect. 
 
3. Firewall Evaluation Criteria 
 
Choosing the right firewall for  an organization can be a daunting task, given the complexity of the 
problem and the wide variety of products to choose from. Yet the following criteria should help the 
security practitioner narrow the list of candidates considerably: 
•  Performance. Firewalls always impact the performance of the connection between the local 
and remote networks. Adding a firewall creates an additional "hop" for network packets to travel through; 
if the firewall must authenticate connections, that creates an additional delay. The firewall machine 
should be powerful enough to make these delays negligible. 
•  Requirements Support. A firewall should support all of the applications that an organization 
wants to use across the two networks. Virtually all firewalls support fundamental protocols like SMTP, 
TELNET, FTP, and HTTP; strong firewalls should include some form of circuit proxy or generic "packet 
relay." The security practitioner should decide what other applications are required (e.g., S-HTTP, etc.) 
and evaluate firewall products accordingly. 
•  Access Control. Even the simplest firewalls support access control based on IP addresses; 
strong firewalls will support user-based access control and authentication. Large organizations should pay 
special attention to whether a given firewall product supports a large number of user profiles and ensure 
that the firewall can accommodate increased user traffic. 
•  Authentication. The firewall must support the authentication requirements of the local 
security policy. If implementation of the local security policy will entail authenticating large numbers of 
users, the firewall should provide convenient yet secure enterprise-wide management of the user 
accounts. Some firewalls only allow the administrator to manage user accounts from a single console; this 
solution isn't good enough for organizations with thousands of users who each need their own 
authentication account. Moreover, there are logistical issues which need to be thought out. For example, 
suppose the local security policy requires authentication of all inbound TELNET connections. How will 
geographically separated users obtain the proper authentication credentials (e.g., passwords, hard tokens, 
etc.)? 
 
•  Physical Security. The local security policy should stipulate the location of the firewall, and 
the hardware should be physically secured to prevent unauthorized access. The firewall must also be able 
to interface with surrounding hardware at this location. 
•  Auditing. The firewall must support the auditing requirements of the local security policy. 
Depending on network bandwidth and the level of event logging, firewall audit trails can become quite 
large. Superior firewalls will include a data reduction tool for parsing audit trails. 
•  Logging and Alarms. What logging and alarms does your security policy require? If the 
security policy dictates that a potential intrusion event trigger an alarm and mail message to the 
administrator, the system must accommodate this requirement. •  Customer Support. What level of customer support does the firewall vendor provide? If your 
organization requires 24-hour-a-day, 365-days-a-year technical support, is it available? Does the vendor 
provide training courses? Is self-help online assistance, such as a Web page or a mailing list, available? 
•  Transparency. How transparent  is the firewall to your users? The more transparent your 
firewall is to your users, the more likely they will be to support it. On the other hand, the more confusing 
or cumbersome your firewall, the more likely your users are to resist it. 
 
There are three different techniques available to firewalls to enforce the local security policy: packet 
filtering, circuit gateways, and application proxies. These techniques are not mutually exclusive; in 
practice, firewalls tend to implement multiple techniques to varying extents.  
 
4. Benefits of Having a Firewall 
 
So how does one obtain management support for implementation of a firewall? The security practitioner 
can point out the protection that a firewall provides: protection of the organization's network from 
intruders, protection of external networks from intruders within the organization, and protection from 
"due care" lawsuits. But the security practitioner can also list the positive benefits a firewall can provide: 
•  Increased ability to enforce network standards and policies. Without a firewall or similar 
device, it is easy for users to implement systems that the Information Services (IS) department doesn't 
know about, that are in violation of organizational standards or policies, or both. In contrast, organizations 
find it very easy to enforce both standards and policies with a firewall that blocks all network connections 
by default. Indeed, it is not uncommon for organizations to discover undocumented systems when they 
implement such a firewall for the first time. 
•  Centralized internetwork audit capability. Since all or most traffic between the two networks 
must pass through the firewall, the firewall is uniquely situated to provide audit trails of all connections 
between the two networks. These audit trails can be extremely useful for investigating suspicious network 
activity, troubleshooting connectivity problems, measuring network traffic flows, and even investigating 
employee fraud, waste, and abuse. 
 5. Limitations of a Firewall 
 
But even with all of these benefits, firewalls still have their limitations. It is important that the security 
practitioner understand these limitations because if these limitations allow risks which are unacceptable to 
management, it is up to the security practitioner to present additional safeguards to minimize these risks. 
The security practitioner must not allow management to develop a false sense of security simply because 
a firewall has been installed. 
•  Firewalls provide no data integrity. It is simply not feasible to check all incoming traffic for 
viruses. There are too many file formats, and often files are sent in compressed form. Any attempt to scan 
incoming files for viruses would severely degrade performance. Firewalls have plenty of processing 
requirements without taking on the additional responsibility of virus detection and eradication. 
•  Firewalls don't protect traffic that is not sent through them. Firewalls can not protect against 
unsecured, dial-up modems attached to systems inside the firewall; against internal attacks; against social 
engineering attacks; or against data that is routed around them. It is not uncommon for an organization to 
install a firewall, then pass data from a legacy system around the firewall because their firewall did not 
support the existing system. 
•  Firewalls may not protect anything if they have been compromised. Although this statement 
should be obvious, many security practitioners fail to educate senior management on its implications. All 
too often senior management approves - either directly or through silence - a security posture which 
positively lacks an internal security policy. Security practitioners cannot allow perimeter security via fire 
walls to become a substitute for internal security. 
•  Firewalls cannot authenticate datagrams at the transport or network layers. A major security 
problem with the TCP/IP protocol is that any machine can forge a packet claiming to be from another 
machine. This means that the firewall has literally no control over how the packet was created. Any 
authentication must be supported in one of the higher layers. 
•  Firewalls provide limited confidentiality. Many firewalls have the ability to encrypt 
connections between two firewalls (using a so-called "virtual private network" or "VPN"), but they 
typically require that the firewall be manufactured by the same vendor. 
 
A firewall is no replacement for good host security practices and procedures. Individual system 
administrators still have the primary responsibility for preventing security incidents. 
 
6. Conclusions 
 
A firewall can only reduce the risk of a breach of security; the only guaranteed way to prevent a 
compromise is to disconnect the network and physically turn all machines off. Moreover, a firewall 
should always be viewed as a supplement to host security; the primary security emphasis should be on 
host security. Nonetheless, a firewall is an important security device which should be used whenever an 
organization needs to protect one network from another. 
 
References 
 
[Bish03]  Bishop, M. - Computer Security Art and Science, Ed. Addison-Wesley, 2003 
[Pfle03]  Pfleeger, C. - Security in Computing, Ed. Prentice Hall, 2003 
[Ghos01]  Ghosh, A. - Security and Privacy for E-Business, Ed. John Wiley & Sons, 2001 
[BaKa02]  Basworth, S., Kabay, M. - Computer Security Handbook – 4
th Edition, Ed. John Wiley 
and Sons, 2002. 
[TiKr02]  Tipton, H., Krause, M. - Information Security Management - Handbook 4th edition, Ed. 
Auerbach, 2002;  

Computer Security Art and Science,

Security and Privacy for E-Business,

Firewall Management

http://www.rebe.rau.ro/RePEc/rau/jisomg/WI07/JISOM-WI07-A18.pdf

Firewall Management

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