How to Start Spanning Tree Protocol Projects Using OMNeT++

To start a Spanning Tree Protocol (STP) project using OMNeT++ that has several steps to make a network, which utilises STP for loop-free topologies within Ethernet networks. STP is utilised making sure that there are no loops within the network by deactivating specific links, and it is normally utilised within switch-based networks which is Layer 2.

While OMNeT++ is mainly utilised to replicate the network protocols then we will adhere to the given method for replicating STP that need to utilise the INET framework or making custom modules for switches, STP behavior, and other network modules. Below is a basic approach to get started with implementing STP in OMNeT++.

Steps to Start Spanning Tree Protocol Projects in OMNeT++

Step 1: Install OMNeT++ and INET Framework

  1. Install OMNeT++:
    • We should download OMNeT++ and install it on the system.
    • Adhere to the provided guidance based on operating system.
  2. Install INET Framework:
    • The INET Framework offers a complete collection of models to replicate the IP networks with switches, routers, and diverse network protocols.
    • Copy INET within GitHub:

git clone https://github.com/inet-framework/inet.git

    • Go to OMNeT++, select Module Manager (in OMNeT++ IDE) and then import the INET framework to the project.

Step 2: Create a New OMNeT++ Project for STP

  1. Create a New OMNeT++ Project:
    • To navigate File > New > OMNeT++ Project and make a new project such as STP_Project in OMNeT++.
  2. Set Up the Network Topology:
    • Make a network topology with switches (or bridge-like devices), which will utilise the Spanning Tree Protocol for topology management.

A simple network instance could have numerous switches and hosts:

network StpNetwork {

submodules:

switch1: Bridge;

switch2: Bridge;

switch3: Bridge;

switch4: Bridge;

host1: StandardHost;

host2: StandardHost;

host3: StandardHost;

host4: StandardHost;

connections:

host1.eth[0] <–> EthernetInterface <–> switch1.eth[0];

host2.eth[0] <–> EthernetInterface <–> switch2.eth[0];

host3.eth[0] <–> EthernetInterface <–> switch3.eth[0];

host4.eth[0] <–> EthernetInterface <–> switch4.eth[0];

switch1.eth[1] <–> EthernetInterface <–> switch2.eth[1];

switch2.eth[2] <–> EthernetInterface <–> switch3.eth[1];

switch3.eth[2] <–> EthernetInterface <–> switch4.eth[1];

switch4.eth[2] <–> EthernetInterface <–> switch1.eth[2];

}

In this case:

  • The Bridge module denotes a switch.
  • The StandardHost module signifies the network hosts.
  • EthernetInterface is utilised for designing the physical network interface.

Step 3: Implement Spanning Tree Protocol (STP)

  1. Create a Custom STP Module: We want to execute the Spanning Tree Protocol for the network switches (or bridges) in a custom module. We can subclass cSimpleModule to make this functionality.

Below is an outline of how we could execute this:

    • Bridge Initialization: Every single switch (bridge) want to execute the STP algorithm for finding the root bridge and active ports.
    • BPDU (Bridge Protocol Data Unit): These switches will transmit BPDU frames periodically to explore and sustain the network topology.
    • STP Timers: We need to execute the timers for forward delay, max age, and hello time to handle the states of STP protocol.

Example structure of a custom Bridge (STP) module:

class StpBridge : public cSimpleModule {

protected:

// Store the root bridge, port state, and timers

int rootBridgeId;

bool portState; // Forwarding or Blocking

simtime_t helloTime;

simtime_t maxAge;

virtual void initialize() override {

// Initialize STP timers and variables (root bridge, port state)

rootBridgeId = getId();  // Assume the switch itself starts as the root

helloTime = 2.0; // Example: Hello Time = 2 seconds

maxAge = 20.0;   // Example: Max Age = 20 seconds

}

virtual void handleMessage(cMessage *msg) override {

// Handle incoming messages (BPDU frames)

if (msg->isSelfMessage()) {

// This could be a timer event

processSTP();

} else {

// Handle incoming BPDU (Bridge Protocol Data Unit)

processBPDU(msg);

}

}

void processBPDU(cMessage *msg) {

// Process incoming BPDU (for BPDU exchange between switches)

// Determine whether this BPDU affects the root bridge or port states

EV << “Received BPDU from ” << msg->getSenderModule()->getId() << endl;

}

void processSTP() {

// Implement logic to send BPDU, manage root bridge election, and port blocking

EV << “Sending BPDU to detect topology changes” << endl;

sendBpdu();

}

void sendBpdu() {

// Create and send a BPDU to other switches

cMessage *bpdu = new cMessage(“BPDU”);

send(bpdu, “out”);

}

// Optionally, implement the process to change port states based on STP algorithm

void updatePortState(bool state) {

portState = state;

if (portState) {

EV << “Port is forwarding” << endl;

} else {

EV << “Port is blocking” << endl;

}

}

};

In this example:

  • rootBridgeId: Monitors the root bridge ID within the network.
  • portState: A flag, which shows whether the port is sending or obstructing.
  • processBPDU(): It supports to manage the incoming BPDU frames from other switches.
  • processSTP():Transmits BPDU frames occasionally and handles STP logic.
  • updatePortState(): Modernizes the port state to forwarding or blocking depends on the STP mechanisms.
  1. Implement the Spanning Tree Algorithm:
    • Root Bridge Election: The switch including lowest bridge ID turn into Root Bridge. Other switches will be utilised this like the root for its topology computation.
    • Port Role Determination: Find whether the port is the root port, designated port, or blocked depends on the topology for each switch.
    • BPDU Exchange: Swap BPDU frames occasionally among the switches, sustaining topology consistency.

Step 4: Configure the Simulation

  1. Configure the Simulation Parameters in omnetpp.ini:
    • Configure the simple network settings, such as network type, switch set up, and BPDU timers.

Example configuration for STP:

network = StpNetwork

sim-time-limit = 100s

[Config StpConfig]

*.switch1.typename = “StpBridge”

*.switch2.typename = “StpBridge”

*.switch3.typename = “StpBridge”

*.switch4.typename = “StpBridge”

# Set STP parameters

*.switch1.helloTime = 2s

*.switch1.maxAge = 20s

*.switch1.forwardDelay = 15s

Now:

  • The helloTime, maxAge, and forwardDelay metrics are portion of the STP timers.
  1. Traffic Generation:
    • Configure the traffic sources like UDP or TCP traffic on the hosts, confirming that data can properly flow after STP meets.

Step 5: Run the Simulation

  1. Build the Project:
    • In OMNeT++, select the Build to execute the project.
  2. Run the Simulation:
    • Execute the simulation to utilise Tkenv or Qtenv.
    • We want to monitor how the switches compute the spanning tree, inactivate specific links, and avoid loops.
  3. Monitor and Analyze:
    • Monitor STP events and BPDU exchanges to utilise EV logging.
    • Examine network topology modifications and confirm that the switches are properly sending and obstructing ports.

Example of logging a BPDU event:

EV << “Sending BPDU from switch ” << getId() << ” to neighbors” << endl;

  1. Verify the Topology:
    • Make sure that the spanning tree meets and that has no loops exist within the network.

Step 6: Extend the Simulation

  1. Handle Topology Changes:
    • We should replicate the addition or removal of switches monitoring how STP responses to topology changes and sets up the spanning tree again.
  2. Scalability:
    • Maximize the network size and then estimate how the STP protocol balances including additional switches.
  3. Simulate Faults:
    • We have to mimic link failures and confirm how STP responds to broken links, resetting the tree if required.

Conclusion

To execute Spanning Tree Protocol (STP) using OMNeT++ which needs to make a custom module for switches (bridges), which manages BPDU exchange, root bridge election, and port state management. When we make network topology, executed the STP protocol, and set up the simulation then we can execute the experiments for monitoring how STP avoids the loops and sustains a loop-free network topology with changes.

Above, we provided structured process for replicating and implementing the Spanning Tree Protocol Projects using OMNeT++ environment and INET framework. If you want additional information on this topic, feel free to ask.

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