What Exactly Is a Collapsed Core Architecture?

In a conventional three-tier network model, the campus network is structured into three distinct layers, each serving a specific function. The core layer plays a pivotal role in inter-site transport and routing, handling critical server and internet connections. The distribution layer manages the connectivity between the core and access layers, while the access layer grants network access to end users, including devices such as PCs and tablets.

While this three-tier model is indispensable for intricate campuses with diverse needs, it’s worth exploring more streamlined options, especially for smaller or medium-sized campus networks. This is where the “Collapsed Core Architecture” comes into play. In this model, the core and distribution layers are merged into a single entity, simplifying the network design and management process.

Benefits of Collapsed Core Networks

The Collapsed Core Network operates in a manner similar to its three-tier counterpart, but it offers unique advantages tailored to the needs of smaller campuses:

1. Lower CostsBy amalgamating the core and distribution layers, a collapsed core network significantly reduces the hardware requirements, resulting in cost savings. This model provides an opportunity to harness the benefits of the three-tiered architecture without breaking the budget.

2. Simplified Network ProtocolsWith only two layers involved in communication, the network’s protocol complexity is reduced, minimizing potential protocol-related issues.

3. Designed for Small CampusesThe collapsed core model is purpose-built for small and medium-sized campuses, ensuring that they can enjoy the advantages of a three-tiered model without the burden of unnecessary equipment or complexity.

Limitations of Collapsed Core Networks

While collapsed core networks offer compelling benefits, they do come with certain limitations, which are essential to consider:

1. ScalabilityCollapsed core networks have limited scalability, making it challenging to accommodate rapid growth in terms of additional sites, devices, and users. Cisco suggests that a small network supports up to 200 devices, while a medium network caters to up to 1000. Beyond this scope, transitioning to a three-tier model may become necessary.

2. ResiliencyThe streamlined design of collapsed core networks means there is less redundancy to mitigate individual component failures. While the network remains reliable, the reduced redundancy does entail some trade-offs in terms of resiliency.

3. ManageabilityThe lower redundancy can complicate the management process, especially when dealing with faulty components or distribution policy adjustments. Careful consideration and planning are required to minimize network downtime during such scenarios.

Is a Collapsed Core Design Right for You?

For small and medium-sized campuses seeking the robustness of a three-tiered network architecture without the associated budget constraints and technical complexities, a collapsed core network can be an ideal solution. However, campuses with rapid growth expectations should be prepared to transition to the full three-tiered design when necessary, as scalability, resiliency, and manageability are considerations that can’t be ignored.

In conclusion, the choice of network architecture ultimately depends on your specific needs, resources, and growth expectations. A collapsed core network offers an efficient compromise between complexity and cost-effectiveness, making it a viable option for many smaller enterprises in their pursuit of a resilient and scalable network infrastructure.

Some useful links to Cisco’s resources on the subject of network architecture and design, specifically focusing on the Collapsed Core Network and related concepts:

1. Cisco Campus Network Design Guide: Cisco’s comprehensive guide on campus network design, which covers various architectural models, including the Collapsed Core Network.

2. Cisco Enterprise Network Architecture: Explore Cisco’s solutions and insights into enterprise network architecture, including resources on designing scalable and resilient networks.

3. Cisco Networking Academy: Access Cisco’s Networking Academy, a resource-rich platform offering courses and materials on network design, configuration, and troubleshooting.

4. Cisco Design Zone: Cisco’s Design Zone provides practical design and deployment guides for various network scenarios, including those relevant to the Collapsed Core Network.

These links will provide readers with valuable information and insights from Cisco, a leading authority in the field of network architecture and design.

Spanning Tree Protocol is a network protocol that provides redundancy while preventing loops in a network. It accomplishes this by creating a loop-free logical topology of a network, while still allowing redundant paths for traffic. It does this by electing one switch in the network as the root bridge, and then blocking redundant links to ensure that there is only one active path between any two switches.

However, while STP provides a solid foundation for network redundancy and loop prevention, it has its limitations. For example, in the event that the root bridge fails, it can take a significant amount of time for the network to converge and find a new root bridge. This downtime can be unacceptable for certain networks, particularly those with critical applications or high availability requirements.

This is where Spanning Tree Protection (STP) comes into play. STP enhances the functionality of STP by providing a faster failover mechanism in the event of a root bridge failure. This mechanism ensures that the network can quickly recover from a failure and continue to function with minimal downtime.

STP accomplishes this by creating multiple active paths between switches while still preventing network loops. This allows for a faster failover in the event of a root bridge failure because the network already has alternate paths available to use. Additionally, STP includes a mechanism for detecting and preventing loops in the network, ensuring that data is always transmitted efficiently and without interruption.

In a core switching environment, STP protection is especially critical. Core switches are the backbone of the network, responsible for routing and transmitting data across the entire network. Any downtime or failure of a core switch can have a significant impact on the network’s performance and availability.

By implementing STP protection on core switches, network administrators can ensure that their networks remain available and reliable even in the face of hardware failures or other issues. Additionally, by leveraging the redundancy provided by STP protection, core switches can be upgraded or replaced without causing downtime or interrupting network traffic.

Root Guard is an extension of the STP protocol that provides additional security by protecting the root bridge from unauthorized access. The root bridge is the switch that has the lowest bridge ID and is responsible for initiating the STP algorithm. An attacker can potentially change the bridge ID of a switch and force it to become the root bridge, allowing them to manipulate network traffic and access sensitive information.

To prevent this, Root Guard is implemented on switches that are not intended to be the root bridge. When Root Guard is enabled, the switch will block any port that receives a BPDU (Bridge Protocol Data Unit) from a switch with a superior bridge ID to the current root bridge. This prevents any unauthorized switch from becoming the root bridge and ensures that the network topology remains stable.

Root Guard can be particularly useful in environments where network security is a high priority, such as in financial institutions, healthcare facilities, and government agencies. By enhancing the STP protocol with Root Guard, network administrators can prevent unauthorized access to critical network resources and improve overall network reliability.

Root Guard is an essential tool for enhancing the reliability and security of Spanning Tree Protocol in network environments. It provides an additional layer of protection against the Root Bridge Attack and ensures that the network topology remains stable and secure. Network administrators should consider implementing Root Guard in their network infrastructure to prevent potential attacks and improve overall network performance.

In conclusion, Spanning Tree Protection is a critical technology for ensuring the reliability and availability of network traffic. By enhancing the capabilities of STP and providing faster failover mechanisms, STP protection is particularly well-suited for core switching environments. Network administrators should carefully consider the benefits of STP protection when designing and implementing their network infrastructure, to ensure that their networks remain available and reliable at all times.

Here are the Cisco IOS commands to secure STP and enable Root Guard:

Enable STP:

switch(config)# spanning-tree mode rapid-pvst

Enable PortFast on access ports:

switch(config)# spanning-tree portfast default
switch(config)# interface interface-id
switch(config-if)# spanning-tree portfast

Enable BPDU Guard on all access ports:

switch(config)# spanning-tree portfast bpduguard default

Enable Root Guard on all non-root bridge ports:

switch(config)# spanning-tree guard root

Verify that Root Guard is enabled:

switch# show spanning-tree interface interface-id
The output should display the "Root guard" status as enabled.

By implementing these Cisco IOS commands, you can secure STP and enable Root Guard to protect against unauthorized access and maintain network stability. It is important to regularly monitor and review the STP configuration to ensure that it is properly secured and optimized for your network environment.

Cisco has some good recommendations – https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/10588-74.html