Network Design With Focus on Security

Holistic approach to designing Cisco Network Security

Network security has historically been approached as a collection of products used primarily to secure the network perimeter or site-to-site connectivity. Today, finding and fixing individual network security holes and point problems are not enough because the cost of security breaches or disruptions is high and can take many forms. These include network downtime, theft of proprietary information, loss of revenue, diminished goodwill, the cost of diverting staff from critical projects to respond to breaches, and reduced IT and business productivity. The availability of sophisticated exploits, the proliferation of software vulnerabilities, and the growing level of terrorist and criminal activity directed at communications networks have heightened the need for network and system security. In addition, networks carry more mission-critical applications than in the past, making the costs of downtime severe and the need to minimize security breaches and downtime crucial.
Security now requires a system-level approach to securing the entire network—the perimeter, data centers, campus LAN,wireless LAN, desktops, and endpoint hosts. Securing the network is an ongoing process that enables the corporation to help ensure the efficient and effective pursuit of corporate missions and goals. Every organization needs a comprehensive network security process that aligns business goals with network capabilities and technical requirements. An effective approach to network security prevents the loss of customer or partner data. It controls resources, complies with regulations, and helps avoid or mitigate potential legal and financial liabilities. It employs designs, processes, and systems that help protect critical resources and facilitate user access. A properly designed and applied security process should be aligned within the framework of a company’s corporate governance, IT governance, and network governance systems. A well-designed network governance model optimizes stakeholder value, recognizing the needs not only of shareholders, but also of customers, suppliers, emplo yees, and other stakeholder communities. A security process that is firmly embedded in and built around network governance will have elements of network security policy, goals, assessment, implementation, and operation.


Design Phases

Prepare Phase

As one enterprise network manager observed, true alignment with the business is necessary in order for IT to provide companies with competitive advantage.In the prepare phase of the network lifecycle, a company establishes business requirements and a corresponding technology vision. The company develops a technology strategy and identifies the technologies that can best support its growth plans. After the financial and business value of migrating to a particular advanced technology solution has been assessed, the company establishes a high-level, conceptual architecture of the proposed system and validates features and functionality documented in the high-level design through proof-of-concept testing.

Plan Phase

In the plan phase of the network lifecycle, a company assesses its network to determine if the existing system infrastructure, sites, and operational environment are able to support its proposed system. The organization tries to make sure that adequate resources are available to manage the technology deployment project from planning through design and implementation. To plan for network security, the company assesses its system, networks, and information against intruders and assesses the network for threat of outside, untrustworthy networks gaining access to internal, trusted networks and systems. A project plan is created to help manage the tasks, risk, problems, responsibilities, critical milestones, and resources required to implement changes to the network. The project plan aligns with the scope, cost, and resource parameters established in the original business requirements.


Design Phase

During the design phase of the network lifecycle, a company develops a comprehensive detailed design that meets current business and technical requirements and incorporates specifications to support availability, reliability, security, scalability,and performance. In addition, the company develops a comprehensive design specific to the technology system’s operations and network management processes and tools. Where applicable, custom applications are created for the technology to meet the organization’s requirements and to enable integration with the existing network infrastructure. A variety of plans is developed during the design phase to guide activities such as configuring and testing connectivity, deploying and commissioning the proposed system, migrating network services, demonstrating network functionality, and validating network operation.


Implement Phase

In the implement phase, a company works to integrate devices without disrupting the existing network or creating points of vulnerability. The company might stage and test the proposed system before deploying it. After identifying and resolving anysystem implementation problems, the company installs, configures, and integrates system components and installs,configures, tests, and commissions the operations and network management system. Once network services have been migrated, the company validates that its operational network is working as intended, validates system operations, and works to close gaps in staff skills.


Operate Phase

Network operations represent a large part of a company’s IT budget. An organization spends substantial time in this phase,living with the technology in the company’s environment. Throughout the operate phase, a company maintains the ongoing health of its system, proactively monitoring and managing it to maximize its performance, capacity, availability, reliability, and security. The company manages and resolves problems or changes affecting its system, replacing or repairing hardware as needed. It makes physical and logical moves, adds, and changes and keeps system software and applications current, and it manages hardware and software suppliers to help ensure efficient delivery of products or services.

Optimize Phase

The paramount goal of the optimize phase is achievement of operational excellence through ongoing efforts to improve the performance and functionality of the system. A company tries to ensure that its operational system is meeting the objectives and requirements established in the company’s business case and works to improve system performance and security. Management practices are enhanced by improving network deployability and operational efficiencies through a network management system that automates, integrates, and simplifies management processes and tools. Business requirements are regularly updated and checked against the network’s technology strategy, performance, and operations. The network must be adaptable and prepared to cope with these new or changing requirements. As it is changed to support new business requirements or to enhance performance, the network reenters the prepare phase of its lifecycle.


Security Development Life Cycle

Security Solutions has defined a development standard called the Security Development Lifecycle (SDL).  This process is designed to ensure that Security Solutions produces secure and resilient products by identifying and implementing specific processes or tools to enable engineers to detect, fix, mitigate and prevent design and code weaknesses that could become exploitable.
SDL  is a multi-layered defensive approach. First, we seek to ensure product security is integrated into the design and design review process through the use of baseline requirements and threat modeling reviews.  secondly, we pursue a rigorous software development design process to detect, fix, and protect against potential software weaknesses. Finally, we utilize robust penetration testing to validate the effectiveness of the first two layers of our defense, and to identify and fix any resulting vulnerabilities.
SDL  utilizes many industry standards and best practices. for example, SDL  tools and processes specifically seek to eliminate common software weakness such as those found in the SANS Top 25, and to utilize Safe C Libraries and OWASP Java libraries.  The aim is also to leverage industry best practices in utilizing threat modeling in design review, static analysis, and standards-based compiler technologies such as Pro-Police or BOSC, and to utilize commonly available or open source penetration testing tools and techniques. Microsoft has also been a valuable partner as both a model for SDL and also as a sounding board for Security Solutions as we developed and adapted their concepts to meet the unique attributes of our development environment and needs.
Security Solutions continuously works to identify secure postures, requirements, and best practices for products.  Once identified, vetted, and agreed upon, they are stored in a common technology repository and incorporated into development methodologies with the expectation that products will comply with all requirements within the applicable common technology.
In addition to robust tools and process for developing products, design and code reviews are critical efforts that are gaining even more internal attention.  While most reviews are performed by senior members of the development team, they may also include individual technical experts, depending on the technology or code under review.  In addition to development team-focused efforts, Security Solutions also has resources to address product security needs such as in-depth review and vulnerability analysis or common criteria review and inspection.  These specialized teams assist in code reviews, penetration tests, and compliance certification activities.
Penetration testing is a critical final development step to ensure that product security mitigation issues have been addressed. Security Solutions utilizes many commonly used commercial and open source fuzzing tools to ensure that we have adequately resolved product weaknesses or identified and fixed potential problems before the product ships.
ISO certification of our development processes, of which SDL  is an inherent part,  provides customers validation and confidence that our processes, such as common technology requirements, secure coding procedures, code reviews, testing and verification, are designed to be consistently executed within our product development. The end goal of the Security  Development Lifecycle methodology is to ensure that our customers can remain confident that the Security Solutions product is robust and resilient in the face of attack.

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Total Visibility
Total visibility consists of the following elements: identity, trust, compliance, event monitoring, and performance monitoring. Key considerations for total visibility include the following:
- Identifying and classifying users, traffic, applications, protocols, and usage behavior
- Monitoring and recording activity and patterns
- Collecting and correlating data from multiple sources to identify trends, and system-wide events
- Detecting and identifying anomalous traffic and threats

Complete Control
Complete control consists of hardening individual devices, increasing the resiliency of the network, isolating users, systems and services, security policy enforcement, and event mitigation. Key considerations for complete control include the following:

- Hardening IT infrastructure, including individual devices and increasing network resiliency
- Limiting access and usage per user, protocol, service, and application
- Isolating users, services, and applications
- Protecting against known threats and exploits
- Dynamically reacting in response to anomalous events


The identify controls deliver the capabilities for a system to identify and classify entities accessing a given resource and to then determine a trust level or state of trust for that entity. Usually, trust is established through mechanisms other than inspection of an IP address, including inspection of credentials. Identifying an entity applies to traffic from within the network and possibly external traffic entering a network.


- Identity-based network solutions (802.1x, NAC, and so on)
- Authentication, Authorization, and Accounting (AAA)—Authentication
- Biometric recognition
- Routing authentication (MD5)
- Secure messaging (encrypted E-mail)
- VPN authentication
– Digital certificates
– Pre-shared keys
– User authentication


Monitor The monitor controls address the fundamental capabilities and instrumentation to facilitate security visibility, combined with the ability to monitor the behavior and usage of the infrastructure components, including resources, connected systems, users, applications, and IP traffic.

- AAA—Accounting
- Anomaly Detection System
- Intrusion Detection System (IDS) and Intrusion Prevention System (IPS)
- Network flow data collection
- Simple Network Management Protocol (SNMP)/Remote Monitoring (RMON)/Management Information Base (MIB)
– CPU, memory threshold
- Syslog
– Topologies: Security Solutions Discovery Protocol (CDP); routing protocols; multiprotocol label switching (MPLS) Label Distribution Protocol (LDP)
- Sinkholes


The correlate controls focus on the ability of the system to derive and present intelligence related to the state of the infrastructure based on correlation and management of visibility data.Correlation is the interpretation, dissemination, analysis, and classification of visibility data into meaningful operational information through the contextualization of seemingly unrelated events or changes. From a security operations perspective, it provides the foundation to apply policy enforcement and isolation controls.


- Analysis of network flow data (Arbor, Security Solutions Security Monitoring, Analysis, and Response System (CS-MARS), and so on)
- Host intrusion protection event correlation
- Security incident management system
- Event analysis and correlation
– Syslog
– Antivirus
- Network Time Protocol (NTP) synchronization

The harden controls address the ability of an infrastructure to withstand, adjust to and/or recover from adverse uncontrolled circumstances. Hardening includes both securing individual devices and the infrastructure as a whole through increased resilience, fault tolerance, route duplication and other means.

- Control plane policing
- Device hardening
– Disable unused services
– Latest patch level
– Restrict device accessibility
- Component redundancy
– Power supply
– Link and interface
- Device redundancy
- Topology redundancy


The isolate controls focus on the ability of a system to limit the scope and minimize the impact upon users, services, and systems from known and unknown disturbances. Implementation of the isolate controls provides the ability to isolate logical and physical functional blocks of an infrastructure into security zones to control or to prevent access between the functional blocks in the infrastructure and to limit the scope of security breech exploitation.

- Firewall access control policies
- Network and segment isolation
- Out of band management
- VPN encryption
- Management traffic encryption—Secure Shell (SSH), SNMP, and so on
- Virtual LAN (VLAN)

The enforce controls deliver the capabilities required to enforce the allowed behavior of connected systems, users, applications, and IP traffic. Policy enforcement may either be static (a control is applied on a permanent basis) or dynamic (a control is applied to specifically mitigate some discrete event or security incident).


- Content filtering
- Distributed-denial-of-service (DDoS) protection
- Host intrusion prevention
- Port security
- Quality-of-Service (QoS) enforcement
- Network access control
– Access control lists (ACL), filters
– Unicast reverse path forwarding (uRFP)
– Anti-spoofing
- Policy-based routing
- AAA authorization



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