What Is Root Guard In Networking


In computer networking, the Spanning Tree Protocol (STP) is used to prevent network loops and ensure redundancy. However, this protocol can be vulnerable to malicious or accidental misconfigurations. Root Guard is a simple yet powerful feature that provides an additional layer of protection against unauthorized switches or bridges. In this article, we will explore what Root Guard is, its benefits, and how to configure and troubleshoot it on Cisco devices. We will also discuss the alternatives and limitations of Root Guard, as well as its future outlook in the context of STP and other network protocols.

1. Introduction to Root Guard

What is Root Guard?

Root Guard is a security feature in switched networks that prevents rogue switches from taking over the network’s root bridge. A rogue switch can be a device that has been improperly configured or a device that has been intentionally connected to the network with the goal of disrupting it.

Why is Root Guard is important in networking?

The root bridge is the central switch in a Spanning Tree Protocol (STP) network. If a rogue switch becomes the root bridge, it can result in network instability, connectivity issues, and even network downtime. Root Guard is a crucial feature in preventing rogue switches from taking over the network’s root bridge and ensuring network stability and security.

2. Overview of Spanning Tree Protocol (STP)

What is Spanning Tree Protocol (STP)?

Spanning Tree Protocol (STP) is a protocol used in network switches to prevent loops in a network topology, which can lead to network malfunctions and outages.

How STP works?

STP works by selecting a single switch to be the root bridge of the network, and then creating a logical tree-like structure that prevents loops from occurring. STP allows for redundant links between switches to be used, but only one link is active at a time, ensuring that there are no loops in the network.

What is computer networking?

Computer networking refers to interconnected computing devices that can exchange data and share resources with each other. These networked devices use a system of rules, called communications protocols, to transmit information over physical or wireless technologies.

What are the types of computer network architecture?
Computer network design falls under two broad categories:

1. Client-server architecture
In this type of computer network, nodes may be servers or clients. Server nodes provide resources like memory, processing power, or data to client nodes. Server nodes may also manage client node behavior. Clients may communicate with each other, but they do not share resources. For example, some computer devices in enterprise networks store data and configuration settings. These devices are the servers in the network. Clients may access this data by making a request to the server machine.

2. Peer-to-peer architecture
In Peer-to-Peer (P2P) architecture, connected computers have equal powers and privileges. There is no central server for coordination. Each device in the computer network can act as either client or server. Each peer may share some of its resources, like memory and processing power, with the entire computer network. For example, some companies use P2P architecture to host memory-consuming applications, such as 3-D graphic rendering, across multiple digital devices.

How does a computer network work?

Nodes and links are the basic building blocks in computer networking. A network node may be data communication equipment (DCE) such as a modem, hub or, switch, or data terminal equipment (DTE) such as two or more computers and printers. A link refers to the transmission media connecting two nodes. Links may be physical, like cable wires or optical fibers, or free space used by wireless networks.

In a working computer network, nodes follow a set of rules or protocols that define how to send and receive electronic data via the links. The computer network architecture defines the design of these physical and logical components. It provides the specifications for the network’s physical components, functional organization, protocols, and procedures.

What do computer networks do?

Computer networks were first created in the late 1950s for use in the military and defense. They were initially used to transmit data over telephone lines and had limited commercial and scientific applications. With the advent of internet technologies, a computer network has become indispensable for enterprises.

Modern-day network solutions deliver more than connectivity. They are critical for the digital transformation and success of businesses today. Underlying network capabilities have become more programmable, automated, and secure.

Modern computer networks can:

Operate virtually

The underlying physical network infrastructure can be logically partitioned to create multiple “overlay” networks. In an overlay computer network, the nodes are virtually linked, and data can be transmitted between them through multiple physical paths. For example, many enterprise networks are overlaid on the internet.

Integrate on a large scale

Modern networking services connect physically distributed computer networks. These services can optimize network functions through automation and monitoring to create one large-scale, high-performance network. Network services can be scaled up or down based on demand.

Respond quickly to changing conditions

Many computer networks are software-defined. Traffic can be routed and controlled centrally using a digital interface. These computer networks support virtual traffic management.

Provide data security

All networking solutions come with in-built security features like encryption and access control. Third-party solutions like antivirus software, firewalls, and antimalware can be integrated to make the network more secure.

What Is Root Guard In Computer Networking

Root Guard

Root guard is an STP feature that is enabled on a port-by-port basis; it prevents a configured port from becoming a root port. Root guard prevents a downstream switch (often misconfigured or rogue) from becoming a root bridge in a topology. Root guard functions by placing a port in an ErrDisabled state if a superior BPDU is received on a configured port. This prevents the configured DP with root guard from becoming an RP.

Root guard is enabled with the interface command spanning-tree guard root. Root guard is placed on designated ports toward other switches that should never become root bridges.

Root guard should be placed on SW2’s Gi1/0/4 port toward SW4 and on SW3’s Gi1/0/5 port toward SW5. This prevents SW4 and SW5 from ever becoming root bridges but still allows for SW2 to maintain connectivity to SW1 via SW3 if the link connecting SW1 to SW2 fails.


Root Guard

Any switch in the network can be designated as the root bridge. But to efficiently forward frames, the positioning of the root bridge should be predetermined in a strategic location. The standard STP does not ensure that the root bridge can be assigned permanently by the administrator.

An enhanced feature of STP is developed to address this issue. The root guard feature enables a way to implement the root bridge deployment in the network.

The root guard assures that the interface on which the root guard is enabled is set as the designated port. Normally, the root bridge ports are all set as designated ports unless two or more root bridge ports are connected. If the bridge receives superior STP Bridge Protocol Data Units (BPDUs) on a root guard-enabled interface, the root guard moves this interface to a root-inconsistent STP state. This root-inconsistent state is effectively equivalent to a listening state. No traffic is forwarded across this interface. In this process, the root guard enforces the position of the root bridge.

root guard

Configuring Root Guard

Configuration on the interface level of root guard for Catalyst 6500/6000 and Catalyst 4500/4000 are shown below:

Switch# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Switch#(config)# interface fastethernet 3/1
Switch#(config-if)# spanning-tree guard root

On the Cisco Switches Catalyst 2900XL, 3500XL, 2950, and 3550, we configure root guard as shown:

Switch# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Switch(config)# interface fastethernet 0/8
Switch(config-if)# spanning-tree rootguard

How to configure Root Guard in Cisco Switches

To enable Root Guard, use following commands.

OmniSecuSW1#configure terminal
OmniSecuSW1(config)#interface giga 0/0
OmniSecuSW1(config-if)#spanning-tree guard root

To disable Root Guard, use following commands.

OmniSecuSW1#configure terminal
OmniSecuSW1(config)#interface giga 0/0
OmniSecuSW1(config-if)#no spanning-tree guard root

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