Appendix C Switch Port Functionality

Spanning Tree Protocol (STP)

Spanning Tree Protocol (STP)

Spanning Tree Protocol (STP) is a link management protocol that provides path redundancy while preventing undesirable loops in the network. For an Ethernet network to function properly, only one active path can exist between any two stations. When two ports on a switch are in a loop, the spanning tree port priority and port path cost setting determine which port to put in the forwarding state and which port to put in the blocking state.

The 802.1Q standard defines the method for running multiple VLANs over single or multiple physical LAN segments and defines a unique spanning tree instance to be created on each of the VLAN instances for all the VLANs in a network.

A mono spanning tree (MST) network lacks some flexibility, compared to a per VLAN spanning tree (PVST) network, which runs one instance of STP per VLAN. One spanning tree is created for every new VLAN created on a FESMIC interface. STP is enabled by default on VLAN 1 and on all newly created VLANs.

Cisco developed PVST+ to allow running several STP instances (even over an 802.1Q network) by using a tunneling mechanism. Although beyond the scope of this document, PVST+ can be briefly described as utilizing a Cisco device to connect a MST zone (typically another vendor’s 802.1Q-based network) to a PVST zone (typically a Cisco 802.1Q-based network). There is no specific configuration to enter in order to achieve this. PVST+ is a spanning tree that allows the coexistence of both PVST and Shared Spanning Tree Protocol (SSTP) in a mixed vendor environment.

The STP described in IEEE 802.1D standard takes a substantial amount of time to converge to a loop free topology. It fails to take advantage of the point-to-point wiring found in modern networks. PVST is enabled on all switch platforms. Rapid Spanning Tree Protocol (RSTP), specified in IEEE 802.1w[9], improves the operation of STP, while maintaining compatibility with equipment based on the (original) 802.1d Spanning Tree standard.

Note The Cisco Shared Spanning Tree Architecture documents use the terms MST and SST to mean “Mono Spanning Tree” and “Shared Spanning Tree” respectively. The IEEE 802.1s[10] uses the same terms but with exactly opposite meanings, i.e. MST is “Multiple Spanning Trees” and SST is” Single Spanning Tree.”

When you connect two Cisco switches through 802.1Q trunks, the switches exchange spanning-tree bridge packet data units (BPDUs) on each VLAN allowed on the trunks. The BPDUs on the native VLAN of the trunk are sent untagged to the reserved IEEE 802.1d spanning-tree multicast MAC address (01-80-C2-00-00-00). The BPDUs on all other VLANs on the trunk are sent tagged to the reserved Shared Spanning Tree Protocol (SSTP).

One spanning tree is created for every new VLAN that is created on the FESMIC. STP is enabled by default on VLAN 1 and on all the newly created VLANs.

PVST and PVST+ are enabled by default on the FESMIC.

For detailed information on how STP works, go to http://www.cisco.com.

Cisco 3200 Series Router Hardware Reference

 

C-8

OL-5816-10

 

 

 

Page 131 Page 133
Page 132
Image 132
Cisco Systems 3200 manual Spanning Tree Protocol STP
Page 131 Page 133

3200 specifications

Cisco Systems 3200 Series routers are designed to deliver high-performance, reliable networking solutions for enterprise and service provider environments. They are part of Cisco's extensive portfolio that addresses the challenges of modern networking, particularly in connecting remote offices and branch locations efficiently and securely.

One of the standout features of the Cisco 3200 Series is its scalability. The routers support a variety of modular interfaces, allowing organizations to tailor their network infrastructure according to specific needs. This modularity ensures that as businesses grow and their networking requirements evolve, the Cisco 3200 can adapt without necessitating a complete overhaul of existing hardware.

Security is another critical characteristic of the Cisco 3200 routers. They incorporate robust security features such as integrated firewall capabilities, advanced encryption standards, and Virtual Private Network (VPN) support. This ensures that sensitive data transmitted over the network is protected from potential threats, making them ideal for businesses that prioritize security, especially in regulated industries.

Performance-wise, the Cisco 3200 is equipped with advanced processing capabilities, enabling it to handle high data throughput even in demanding environments. This performance is bolstered by the use of Cisco's proprietary technologies, such as Quality of Service (QoS) and traffic shaping, which allow the prioritization of critical applications to ensure seamless connectivity.

The router series also benefits from Cisco's extensive software ecosystem, which includes Cisco IOS (Internetwork Operating System). IOS provides a familiar interface for network administrators, alongside a wealth of features for configuration and management. Furthermore, the Cisco 3200 Series is designed to integrate with Cisco's Application Policy Infrastructure Controller (APIC) and Software-Defined Networking (SDN) solutions, offering enhanced flexibility in managing network resources.

Connectivity options for the Cisco 3200 Series are extensive, offering support for various WAN technologies, including MPLS, LTE, and broadband internet. This versatility enables organizations to choose the best connectivity solutions according to their geographic and operational requirements.

Finally, the Cisco 3200 Series routers are built with reliability in mind. They are designed for high availability and redundancy, ensuring that network services remain uninterrupted in the event of hardware failures or maintenance activities.

In conclusion, Cisco Systems 3200 routers represent a comprehensive networking solution, combining scalability, security, performance, and reliability, making them a preferred choice for organizations looking to enhance their networking infrastructure in a dynamic digital landscape.
Top Page Image Contents