How to Begin Implement OSPF Routing in NS3

To begin the OSPF (Open Shortest Path First) in NS-3 has includes the build a routing protocol which dynamically creates the routing tables for link state advertisements (LSAs) and Dijkstra’s shortest path procedures. OSPF is a link-state routing protocol generally used in IP networks.

Here’s how you can begin implementing OSPF Routing in NS-3:

Steps to Begin Implement OSPF Routing in NS3

Step 1: Understand OSPF

1. Key Concepts:
   • Link-State Advertisements (LSAs): Nodes like routers are modifying the LSAs encompass the link state data.
   • Topology Database: Every router has created a comprehensive view for the network topology from LSAs.
   • Shortest Path First (SPF): Uses Dijkstra’s procedures for estimate the shortest paths from the network topology database.
   • Areas: OSPF helps for hierarchical routing areas such as optional for basic implementation.
2. Message Types:
   • Hello: Determine and retain the neighbor relationships.
   • Database Description (DBD): Summarize the network topology data.
   • Link-State Request (LSR): Request the detailed LSAs.
   • Link-State Update (LSU): It has a forwarding LSAs.
   • Link-State Acknowledgment (LSAck): Recognize the receipt for LSAs.

Step 2: Set Up NS-3 Environment

1. Create a Protocol Directory:
   • Generate a new directory below src/, e.g., src/ospf-routing/.
2. Add Required Files:
   • ospf-routing-protocol.h: Header file designed for OSPF protocol.
   • ospf-routing-protocol.cc: execute the file.
   • ospf-routing-helper.h and ospf-routing-helper.cc: Helper classes.
3. Update Build System:
   • Change the wscript in src/ for contains the new OSPF component.

Step 3: Design OSPF Protocol

Define the Protocol Class

Cover the Ipv4RoutingProtocol to apply OSPF functionality.

Header File (ospf-routing-protocol.h)

#include “ns3/ipv4-routing-protocol.h”

#include “ns3/socket.h”

#include “ns3/timer.h”

#include <map>

#include <set>

class OspfRoutingProtocol : public ns3::Ipv4RoutingProtocol {

public:

static ns3::TypeId GetTypeId (void);

OspfRoutingProtocol ();

virtual ~OspfRoutingProtocol ();

// Override Ipv4RoutingProtocol methods

virtual ns3::Ptr<ns3::Ipv4Route> RouteOutput (

ns3::Ptr<const ns3::Packet> packet,

const ns3::Ipv4Header &header,

ns3::Ptr<ns3::NetDevice> oif,

ns3::Socket::SocketErrno &sockerr);

virtual bool RouteInput (

ns3::Ptr<const ns3::Packet> packet,

const ns3::Ipv4Header &header,

ns3::Ptr<const ns3::NetDevice> idev,

ns3::UnicastForwardCallback ucb,

ns3::MulticastForwardCallback mcb,

ns3::LocalDeliverCallback lcb,

ns3::ErrorCallback ecb);

void SendHello ();

void ProcessHello (ns3::Ptr<const ns3::Packet> packet);

void ProcessLsa (ns3::Ptr<const ns3::Packet> packet);

void FloodLsa ();

void ComputeShortestPaths ();

private:

struct LinkState {

ns3::Ipv4Address neighbor;

uint32_t cost;

};

struct NodeState {

ns3::Ipv4Address nodeAddress;

std::vector<LinkState> neighbors;

};

ns3::Ipv4Address m_selfAddress;

std::map<ns3::Ipv4Address, NodeState> m_topologyDatabase; // Topology database

std::map<ns3::Ipv4Address, ns3::Ipv4Address> m_routingTable; // Destination -> Next hop

ns3::Timer m_helloTimer; // Periodic Hello timer

ns3::Timer m_lsaTimer;   // Periodic LSA flooding timer

};

Implement Core Functions

Hello Message Exchange

Determine the neighbors using Hello messages.

void OspfRoutingProtocol::SendHello () {

ns3::Ptr<ns3::Packet> helloPacket = ns3::Create<ns3::Packet> ();

// Serialize Hello message

// …

// Broadcast Hello message

m_socket->SendTo(helloPacket, 0, ns3::InetSocketAddress(ns3::Ipv4Address::GetBroadcast(), 89));

// Schedule next Hello

m_helloTimer.Schedule(ns3::Seconds(10.0));

}

void OspfRoutingProtocol::ProcessHello (ns3::Ptr<const ns3::Packet> packet) {

// Deserialize Hello message

ns3::Ipv4Address neighbor = …; // Extract neighbor address

// Add neighbor to topology database

m_topologyDatabase[m_selfAddress].neighbors.push_back({neighbor, 1}); // Example cost = 1

}

Flood LSAs

Distribute the network topology data using LSAs.

void OspfRoutingProtocol::FloodLsa () {

ns3::Ptr<ns3::Packet> lsaPacket = ns3::Create<ns3::Packet> ();

// Serialize LSA with current topology

// …

// Broadcast LSA

m_socket->SendTo(lsaPacket, 0, ns3::InetSocketAddress(ns3::Ipv4Address::GetBroadcast(), 89));

// Schedule next LSA flooding

m_lsaTimer.Schedule(ns3::Seconds(30.0));

}

Process LSAs

Bring up-to-date the topology database after receiving the LSAs.

void OspfRoutingProtocol::ProcessLsa (ns3::Ptr<const ns3::Packet> packet) {

// Deserialize LSA

NodeState nodeState = …; // Extract node state

// Update topology database

m_topologyDatabase[nodeState.nodeAddress] = nodeState;

// Recompute shortest paths

ComputeShortestPaths ();

}

Compute Shortest Paths

Use Dijkstra’s procedure has calculate the shortest paths.

void OspfRoutingProtocol::ComputeShortestPaths () {

std::set<ns3::Ipv4Address> visited;

std::map<ns3::Ipv4Address, uint32_t> distances;

std::map<ns3::Ipv4Address, ns3::Ipv4Address> previous;

// Initialize distances

for (const auto &entry : m_topologyDatabase) {

distances[entry.first] = std::numeric_limits<uint32_t>::max();

}

distances[m_selfAddress] = 0;

// Dijkstra’s algorithm

while (visited.size() < m_topologyDatabase.size()) {

ns3::Ipv4Address currentNode = …; // Find node with the smallest distance

for (const auto &neighbor : m_topologyDatabase[currentNode].neighbors) {

uint32_t newDistance = distances[currentNode] + neighbor.cost;

if (newDistance < distances[neighbor.neighbor]) {

distances[neighbor.neighbor] = newDistance;

previous[neighbor.neighbor] = currentNode;

}

}

visited.insert(currentNode);

}

// Build routing table

for (const auto &entry : previous) {

m_routingTable[entry.first] = entry.second;

}

}

Packet Forwarding

Sending the packets is using the routing table.

ns3::Ptr<ns3::Ipv4Route> OspfRoutingProtocol::RouteOutput (

ns3::Ptr<const ns3::Packet> packet,

const ns3::Ipv4Header &header,

ns3::Ptr<ns3::NetDevice> oif,

ns3::Socket::SocketErrno &sockerr) {

ns3::Ptr<ns3::Ipv4Route> route = ns3::Create<ns3::Ipv4Route> ();

auto it = m_routingTable.find(header.GetDestination());

if (it != m_routingTable.end()) {

route->SetGateway(it->second);

route->SetOutputDevice(oif);

return route;

} else {

sockerr = ns3::Socket::ERROR_NOROUTETOHOST;

return nullptr;

}

}

Step 4: Write a Helper Class

Generate a helper class to clarify the incorporation.

#include “ospf-routing-protocol.h”

class OspfRoutingHelper {

public:

void Install (ns3::NodeContainer nodes) {

for (auto it = nodes.Begin(); it != nodes.End(); ++it) {

ns3::Ptr<OspfRoutingProtocol> protocol = ns3::CreateObject<OspfRoutingProtocol>();

(*it)->AggregateObject(protocol);

}

}

};

Step 5: Write a Simulation Script

Example Simulation Script

#include “ns3/core-module.h”

#include “ns3/network-module.h”

#include “ns3/internet-module.h”

#include “ospf-routing-helper.h”

using namespace ns3;

int main (int argc, char *argv[]) {

NodeContainer nodes;

nodes.Create (5);

InternetStackHelper stack;

stack.Install (nodes);

OspfRoutingHelper ospfHelper;

ospfHelper.Install (nodes);

PointToPointHelper p2p;

p2p.SetDeviceAttribute (“DataRate”, StringValue (“10Mbps”));

p2p.SetChannelAttribute (“Delay”, StringValue (“2ms”));

p2p.Install (nodes.Get (0), nodes.Get (1));

p2p.Install (nodes.Get (1), nodes.Get (2));

// Additional links…

Simulator::Run ();

Simulator::Destroy ();

return 0;

}

Step 6: Compile and Run

1. Build the Protocol:

./waf configure

./waf build

1. Run the Simulation:

./waf –run your-script

Step 7: Analyze and Extend

1. Tracing Tools:
   • Use AsciiTraceHelper or PcapHelper for examine the congestion.
2. Enhancements:
   • Enhance the OSPF zones for hierarchical routing.
   • Execute the dynamic connection costs according to their congestion or latency.

We had demonstrated about the Open Shortest Path First projects simulation explanations that were enforce in ns3 tool. Also we expand further information regarding Open Shortest Path First.