To simulate Spanning Tree Protocol (STP) in OMNeT++ has needs to execute or utilize a traditional STP routing technique, setting up the network topology to manage multiple redundant paths (which STP eradicates to prevent loops), and monitoring how the protocol generates a loop-free tree.
Here’s a step-by-step guide on how to simulate an STP routing project using OMNeT++ and the INET framework.
Steps to Simulate Spanning Tree Protocol Routing Projects in OMNeT++
- Set up OMNeT++ and INET Framework
- Install OMNeT++: If you haven’t already, download and install OMNeT++.
- Install INET Framework: INET deliver pre-built network protocols and models that can be prolonged to execute STP. We can download it from INET GitHub or utilize the OMNeT++ package manager.
- Understand Spanning Tree Protocol (STP)
- STP Overview: The Spanning Tree Protocol is utilized in Layer 2 switching networks to mitigate loops in the network by generating a loop-free spanning tree. STP performs by:
- Electing a root bridge (switch).
- Calculating the shortest path to the root bridge for each switch.
- Blocking redundant paths to mitigate loops.
- Define a Redundant Network Topology (NED File)
STP is usually implemented in networks with redundant paths, so describe a network with multiple switches and hosts that have redundant connections.
Example NED file with redundant connections between switches:
network STPNetwork
{
parameters:
@display(“bgb=800,600”);
submodules:
switchA: Switch {
@display(“i=abstract/switch”);
}
switchB: Switch {
@display(“i=abstract/switch”);
}
switchC: Switch {
@display(“i=abstract/switch”);
}
switchD: Switch {
@display(“i=abstract/switch”);
}
hostA: StandardHost {
@display(“i=device/pc”);
}
hostB: StandardHost {
@display(“i=device/pc”);
}
connections:
// Redundant links between switches
switchA.pppg++ <–> EthernetLink <–> switchB.pppg++;
switchA.pppg++ <–> EthernetLink <–> switchC.pppg++;
switchB.pppg++ <–> EthernetLink <–> switchD.pppg++;
switchC.pppg++ <–> EthernetLink <–> switchD.pppg++;
// Hosts connected to switches
hostA.ethg++ <–> EthernetLink <–> switchA.ethg++;
hostB.ethg++ <–> EthernetLink <–> switchD.ethg++;
}
In this topology:
- There are redundant links among the switches switchA, switchB, switchC, and switchD.
- The task of STP is to block certain redundant links to make sure no loops are formed while still delivered the connectivity among all hosts.
- Implement or Use Spanning Tree Protocol (STP)
The INET framework doesn’t have a pre-implemented STP, so we can either:
- Implement STP in C++: compose a custom STP algorithm, that contain:
- Root bridge election: The switch with the lowest bridge ID becomes the root.
- Path cost calculation: Each switch determines the least-cost path to the root.
- Blocking redundant links: Non-optimal links are put into a “blocking” state.
- Use an External STP Implementation: we can identify open-source implementations of STP and combine them with OMNeT++ by prolonging INET’s Layer 2 switch behaviour.
Example Custom C++ STP Implementation
Here’s a simplified view of how we need to start writing an STP module in C++:
class SpanningTreeProtocol : public cSimpleModule
{
private:
bool isRoot; // True if this switch is the root
int bridgeID; // Unique bridge identifier for the switch
std::map<int, int> portCosts; // Cost of each port to reach the root
std::map<int, bool> portBlocked; // Whether each port is blocked
protected:
virtual void initialize() override;
virtual void handleMessage(cMessage *msg) override;
void electRootBridge();
void calculatePathCosts();
void blockRedundantLinks();
};
void SpanningTreeProtocol::initialize()
{
// Initialize the switch parameters, including setting a unique bridge ID
bridgeID = par(“bridgeID”);
isRoot = false;
}
void SpanningTreeProtocol::handleMessage(cMessage *msg)
{
// Handle STP messages for root bridge election and path cost calculation
}
void SpanningTreeProtocol::electRootBridge()
{
// Logic for root bridge election based on the lowest bridge ID
}
void SpanningTreeProtocol::calculatePathCosts()
{
// Calculate the least-cost paths to the root bridge
}
void SpanningTreeProtocol::blockRedundantLinks()
{
// Logic to block non-optimal links to prevent loops
}
- Root Bridge Election: The technique should begin by defining which switch will perform as the root bridge according to the lowest bridge ID.
- Path Cost Calculation: Each switch estimates its distance to the root and selects the shortest path.
- Link Blocking: After the calculation, redundant paths are placed in a blocking state to mitigate loops.
- Configure Simulation in omnetpp.ini
We need to set up the simulation parameters in the omnetpp.ini file. We will require specifying metrics for the STP algorithm that contain the bridgeID for each switch.
Example configuration:
network = STPNetwork
sim-time-limit = 200s
# Configure unique bridge IDs for switches
*.switchA.bridgeID = 1
*.switchB.bridgeID = 2
*.switchC.bridgeID = 3
*.switchD.bridgeID = 4
# Enable STP on all switches
*.switchA.hasSTP = true
*.switchB.hasSTP = true
*.switchC.hasSTP = true
*.switchD.hasSTP = true
# Host packet generation settings for testing
*.hostA.numPackets = 100
*.hostA.destAddress = “hostB”
- Simulate and Analyse the Results
Execute the simulation to track the behaviour of the Spanning Tree Protocol. After the root bridge is elected, the switches should estimate the paths to the root and block redundant links. Key parameters to evaluate that include:
- Loop-Free Topology: Make sure the network has no loops and that all hosts are reachable across the spanning tree.
- Path Efficiency: Validate that STP is blocking only the redundant links since maintaining connectivity.
- Convergence Time: Evaluate the time taken for the STP to converge (i.e., for the switches to agree on the final spanning tree).
- Traffic Flow: Make sure that packets are successfully routed among hosts without any loops or dropped packets.
- Extend the Project
Once the basic STP simulation is working, we can prolong it with the following characteristics:
- Link Failures: Familiarize link or switch failures to track on how STP recalculates the spanning tree.
- Multiple VLAN Support: Execute multiple VLANs and replicate Per-VLAN Spanning Tree Protocol (PVST) for diverse VLANs.
- Optimizations: Discover optimizations or extensions to STP, like Rapid Spanning Tree Protocol (RSTP) for faster convergence.
Example Project Structure
STPSimulation/
├── src/
│ └── STPNetwork.ned # Network topology
│ └── SpanningTreeProtocol.cc # Custom STP algorithm
├── omnetpp.ini # Simulation configuration
└── Makefile # Build file
Conclusion
To replicate the Spanning Tree Protocol (STP) in OMNeT++ has needs to generate a redundant network topology and executing or incorporating the STP algorithm to handle the network’s loop-free configuration. We have all the needed tools and resources to get your work done, drop us a message we will guide you with best assistance and detailed explanation.
In this process, we had detailed covered the information about Spanning Tree Protocol simulation procedures and evaluation process of Spanning Tree Protocol outcomes across the OMNeT++ tool. Further details regarding the Spanning Tree Protocol will be provided in upcoming manuals.
