Micro segmentation has many security benefits. As previously discussed, it can be very effective in preventing specific unwanted traffic flows within a VLAN segment. One specific use case of micro segmentation may be to restrict the spreading of malware laterally within a VLAN (that is, spreading of malware to neighboring devices) by only permitting specific protocols that are expected across a network. As an example, a micro segmentation policy would allow a network administrator to instruct the network to allow only PCs with a UC client, such as Cisco Jabber, to establish VoIP calls with other PCs running the Jabber client over specific TCP/UDP ports that have been designated for UC. This type of granularity allows UC clients such as Jabber to function exactly as a user expects by supporting all of the UC features, such as instant messaging, VoIP/video calling, and content sharing. It also helps meet security requirements to minimize the attack surface on a network by denying specific protocols that may traditionally be used by worms, malware, or an attacker.
Customers who previously had requirements to restrict access within a network segment such as a VLAN have traditionally been limited to either VLANs, with VLAN ACLs (VACLs), or private VLANs. Two different modern architectures that provide micro segmentation capabilities are Cisco Software-Defined Access (SDA) and Cisco TrustSec, which offer security policy based on scalable groups. The next section provides an introduction to the SDA solution while also highlighting how TrustSec can be incorporated into SDA to obtain a deeper level of granularity for restricting traffic flows within a network.
Cisco SDA is a solution within the Cisco digital network architecture (DNA) that provides software-defined networking for the campus environment. SDA provides network security by facilitating end-to-end segmentation of network traffic between users, devices, and applications. A software-defined network, providing centralized management, allows organizations to enable security features on a more aggressive basis because there is less of a burden for enabling security across network devices on a device-by-device basis, which is often a reason that networks are not as secure as they could be. SDA also provides organizations with a means and methodology for increasing visibility of network traffic and applying network policy to wired and wireless network devices (such as switches and access points) in an automated manner as a user or devices move around a network. Using the earlier example with Jabber, SDA would ensure that the security policy that has been assigned to a user with a Jabber client will stay with that user while roaming between different places in the network (e.g., desk, conference room, cafeteria).
This type of security approach requires a paradigm shift when compared to a traditional approach of managing ACLs that are applied to network devices to protect specific IP subnets. Using an architecture, such as SDA, security controls are no longer based on IP subnets. Security controls are associated with the identity of a user or device. This is why a policy can still be assigned to users as they roam around a network. The following components are required to support SDA:
▪ Cisco DNA Center (DNA-C): This component provides centralized management of network infrastructure; it is used to create policies (e.g., security, QoS) and automate provisioning of software features and images across network devices. It also provides visibility into network incidents, network telemetry, and analytics.
▪ Cisco Identity Services Engine (ISE): This component integrates with DNA-C to provide access controls (e.g., ACLs, dynamic VLAN assignments), group-based policy, and policy enforcement. It integrates with external repositories such as Active Directory for authentication and authorization.
▪ Network infrastructure (wired and wireless): This infrastructure includes network devices, such as Catalyst switches and access points.
The last element that is included inside an SDA solution is the network fabric. The network fabric is essentially a virtual network that is overlaid on top of the existing physical network with a separate control and forwarding plane. The separation of the control plane from the forwarding plane helps improve the overall performance and scalability of the solution while also simplifying policy, provisioning, and management. As an example, it allows network administrators to provide a consistent policy to a user/device as it moves around the network. To do this, DNA-C and ISE work in unison with network devices to enforce policy that either permits or denies the different types of traffic allowed across a segment of the network. Figure 3-1 depicts a sample SDA solution.
Now that we have introduced SDA, we must also introduce a few more key terms regarding how the SDA solution provides security:
▪ Virtual network: This network provides logical separation (macro segmentation) between devices and other virtual networks. This is analogous to a Virtual Route Forwarding technology.
▪ Scalable group: This mechanism for grouping functions or devices is based on business roles (e.g., employee, contractor, finance, printers, IP phones). Once a group is created, a unique scalable group tag (SGT) is assigned to the scalable group to provide micro segmentation. This security concept is based on Cisco TrustSec.
▪ Contracts: These are used for enforcing policies that have been created within DNA-C to specifically permit or deny certain types of traffic. They are also known as security group ACLs (SGACLs).
At the time of configuration, an administrator needs to align to the virtual networks that have been previously defined by an organization. Because we have been discussing how to create a micro segmentation policy to support UC security within DNA-C, we can use DNA-C as the central place of management and policy configuration. To follow this example, you should take the following steps:
1. Define virtual networks (e.g., ACME_HQ).
2. Define scalable groups (e.g., ACME_UC, ACME_WIDGETS, Employees, Contractors, Printers).
3. Assign scalable groups to virtual networks. This process allows access to resources within a virtual network (e.g., it allows employees and contractors to communicate with IP phones and printers).
4. Create contracts (e.g., Permit_VoiceUDP) that specify the traffic flows that are allowed within scalable groups using SGACLs.
5. Deploy the micro segmentation policy to network devices.
Once the scalable groups and the associated contracts are defined in DNA-C, they are then also shared with ISE over a RESTful API. This setup allows ISE to be the authoritative point of security enforcement across the network. An example illustrating how ISE imports the policy from DNA-C and creates security group ACLs to enforce policy is included in Figure 3-4.
Due to the simplicity involved in this type of workflow, organizations are able to respond to new security threats while reducing operational costs by using a centralized policy engine such as DNA-C. As the threat landscape continues to grow, organizations may need to adopt micro segmentation capabilities to gain more granular security controls instead of the traditional macro-based segmentation approach. It is beyond the scope of this chapter to cover all of the necessary steps needed to design, configure, and provision VRF, DNA-C, ISE, and the network to support SDA. For additional information about SDA, visit www.cisco.com/go/sda.