To implement OSPF (Open Shortest Path First) routing in ns3, we have to create a custom routing protocol class which has similar behavior of OSPF, which incorporates link-state advertisements and Dijkstra’s algorithm for calculating the shortest path.
The built-in implementation of OSPF called OSPF Routing Protocol is already supported by ns3, but for the learning purpose, let’s implement a basic version of OSPF in ns3.
Steps for implementation
- Set up your ns3 :
- Make sure that ns3 is installed in the computer. If not, install it.
- Include necessary libraries :
- In your script, include the necessary libraries.
- Define network topology :
- For your network topology, create the nodes and links.
- Install Internet Stack :
- On your nodes, install the internet stack.
- Implement the OSPF Routing Protocol :
- Create a custom routing protocol class to implement the behavior of OSPF.
- Integrate the Custom Routing Protocol :
- On the ns3 stack, integrate your custom routing protocol.
- Set Up Applications :
- To generate traffic and test the routing, install applications.
- Run the Simulation :
- Define the simulation parameters and run it.
Example implementation in C++
Here is a complete example on implementing a basic OSPF-like routing protocol in ns3:
Include libraries :
#include “ns3/core-module.h”
#include “ns3/network-module.h”
#include “ns3/internet-module.h”
#include “ns3/point-to-point-module.h”
#include “ns3/applications-module.h”
#include “ns3/ipv4-routing-protocol.h”
#include “ns3/ipv4-list-routing-helper.h”
#include <map>
#include <vector>
Define network topology
using namespace ns3;
int main(int argc, char *argv[]) {
CommandLine cmd;
cmd.Parse(argc, argv);
NodeContainer nodes;
nodes.Create(4);
PointToPointHelper pointToPoint;
pointToPoint.SetDeviceAttribute(“DataRate”, StringValue(“5Mbps”));
pointToPoint.SetChannelAttribute(“Delay”, StringValue(“2ms”));
NetDeviceContainer devices01 = pointToPoint.Install(nodes.Get(0), nodes.Get(1));
NetDeviceContainer devices12 = pointToPoint.Install(nodes.Get(1), nodes.Get(2));
NetDeviceContainer devices23 = pointToPoint.Install(nodes.Get(2), nodes.Get(3));
NetDeviceContainer devices30 = pointToPoint.Install(nodes.Get(3), nodes.Get(0));
InternetStackHelper stack;
stack.Install(nodes);
Ipv4AddressHelper address;
address.SetBase(“10.1.1.0”, “255.255.255.0”);
Ipv4InterfaceContainer interfaces01 = address.Assign(devices01);
address.SetBase(“10.1.2.0”, “255.255.255.0”);
Ipv4InterfaceContainer interfaces12 = address.Assign(devices12);
address.SetBase(“10.1.3.0”, “255.255.255.0”);
Ipv4InterfaceContainer interfaces23 = address.Assign(devices23);
address.SetBase(“10.1.4.0”, “255.255.255.0”);
Ipv4InterfaceContainer interfaces30 = address.Assign(devices30);
Implement the OSPF Routing Protocol :
Create a new header file ospf-routing.h :
#ifndef OSPF_ROUTING_H
#define OSPF_ROUTING_H
#include “ns3/ipv4-routing-protocol.h”
#include “ns3/ipv4.h”
#include “ns3/net-device.h”
#include “ns3/ptr.h”
#include “ns3/socket.h”
#include <map>
#include <vector>
#include <set>
namespace ns3 {
class OspfRouting : public Ipv4RoutingProtocol {
public:
static TypeId GetTypeId(void);
OspfRouting();
virtual ~OspfRouting();
virtual Ptr<Ipv4Route> RouteOutput(
Ptr<Packet> p, const Ipv4Header &header,
Ptr<NetDevice> oif, Socket::SocketErrno &sockerr);
virtual bool RouteInput(
Ptr<const Packet> p, const Ipv4Header &header,
Ptr<const NetDevice> idev,
UnicastForwardCallback ucb, MulticastForwardCallback mcb,
LocalDeliverCallback lcb, ErrorCallback ecb);
virtual void NotifyInterfaceUp(uint32_t interface);
virtual void NotifyInterfaceDown(uint32_t interface);
virtual void NotifyAddAddress(uint32_t interface,
Ipv4InterfaceAddress address);
virtual void NotifyRemoveAddress(uint32_t interface,
Ipv4InterfaceAddress address);
virtual void SetIpv4(Ptr<Ipv4> ipv4);
void Start();
private:
void SendLinkStateAdvertisement();
void ReceiveLinkStateAdvertisement(Ptr<Socket> socket);
void CalculateShortestPaths();
void UpdateRoutingTable();
Ptr<Ipv4> m_ipv4;
std::map<Ipv4Address, std::set<Ipv4Address>> m_linkStateDatabase;
std::map<Ipv4Address, Ipv4Address> m_routingTable;
std::map<uint32_t, Ptr<Socket>> m_socketMap;
Time m_updateInterval;
EventId m_updateEvent;
};
}
#endif // OSPF_ROUTING_H
Create the corresponding implementation file ospf-routing.cc:
#include “ospf-routing.h”
#include “ns3/log.h”
#include “ns3/ipv4-routing-table-entry.h”
#include “ns3/simulator.h”
#include “ns3/inet-socket-address.h”
#include “ns3/ipv4-header.h”
namespace ns3 {
NS_LOG_COMPONENT_DEFINE(“OspfRouting”);
NS_OBJECT_ENSURE_REGISTERED(OspfRouting);
TypeId OspfRouting::GetTypeId(void) {
static TypeId tid = TypeId(“ns3::OspfRouting”)
.SetParent<Ipv4RoutingProtocol>()
.SetGroupName(“Internet”)
.AddConstructor<OspfRouting>();
return tid;
}
OspfRouting::OspfRouting() : m_updateInterval(Seconds(10)) {
NS_LOG_FUNCTION(this);
Simulator::Schedule(Seconds(1.0), &OspfRouting::Start, this);
}
OspfRouting::~OspfRouting() {
NS_LOG_FUNCTION(this);
}
void OspfRouting::SetIpv4(Ptr<Ipv4> ipv4) {
NS_LOG_FUNCTION(this << ipv4);
m_ipv4 = ipv4;
}
void OspfRouting::Start() {
NS_LOG_FUNCTION(this);
SendLinkStateAdvertisement();
m_updateEvent = Simulator::Schedule(m_updateInterval, &OspfRouting::Start, this);
}
void OspfRouting::SendLinkStateAdvertisement() {
NS_LOG_FUNCTION(this);
Ptr<Packet> packet = Create<Packet>();
for (auto const &entry : m_linkStateDatabase) {
Ipv4Address node = entry.first;
for (auto const &neighbor : entry.second) {
Ipv4Header header;
header.SetSource(node);
header.SetDestination(neighbor);
packet->AddHeader(header);
}
}
for (uint32_t i = 0; i < m_ipv4->GetNInterfaces(); ++i) {
Ptr<Socket> socket = m_socketMap[i];
socket->SendTo(packet, 0, InetSocketAddress(Ipv4Address::GetBroadcast(), 80));
}
}
void OspfRouting::ReceiveLinkStateAdvertisement(Ptr<Socket> socket) {
NS_LOG_FUNCTION(this);
Ptr<Packet> packet = socket->Recv();
Ipv4Header header;
packet->RemoveHeader(header);
Ipv4Address source = header.GetSource();
Ipv4Address dest = header.GetDestination();
m_linkStateDatabase.insert(dest);
CalculateShortestPaths();
}
void OspfRouting::CalculateShortestPaths() {
NS_LOG_FUNCTION(this);
// Implement Dijkstra’s algorithm to calculate shortest paths
// This is a simplified example and may need more details
// for a complete OSPF implementation
std::map<Ipv4Address, uint32_t> distances;
std::map<Ipv4Address, Ipv4Address> previous;
for (auto const &entry : m_linkStateDatabase) {
distances[entry.first] = std::numeric_limits<uint32_t>::max();
}
Ipv4Address source = m_ipv4->GetAddress(1, 0).GetLocal();
distances = 0;
std::set<Ipv4Address> nodes;
for (auto const &entry : m_linkStateDatabase) {
nodes.insert(entry.first);
}
while (!nodes.empty()) {
Ipv4Address u;
uint32_t minDistance = std::numeric_limits<uint32_t>::max();
for (auto const &node : nodes) {
if (distances[node] < minDistance) {
minDistance = distances[node];
u = node;
}
}
nodes.erase(u);
for (auto const &neighbor : m_linkStateDatabase[u]) {
uint32_t alt = distances[u] + 1; // Assuming unit weight for each edge
if (alt < distances[neighbor]) {
distances[neighbor] = alt;
previous[neighbor] = u;
}
}
}
m_routingTable.clear();
for (auto const &entry : previous) {
m_routingTable[entry.first] = entry.second;
}
}
Ptr<Ipv4Route> OspfRouting::RouteOutput(
Ptr<Packet> p, const Ipv4Header &header, Ptr<NetDevice> oif,
Socket::SocketErrno &sockerr) {
NS_LOG_FUNCTION(this << p << header << oif << sockerr);
Ipv4Address dest = header.GetDestination();
if (m_routingTable.find(dest) == m_routingTable.end()) {
sockerr = Socket::ERROR_NOROUTETOHOST;
return 0;
}
Ptr<Ipv4Route> route = Create<Ipv4Route>();
route->SetDestination(dest);
route->SetGateway(m_routingTable[dest]);
route->SetOutputDevice(oif);
return route;
}
bool OspfRouting::RouteInput(
Ptr<const Packet> p, const Ipv4Header &header,
Ptr<const NetDevice> idev, UnicastForwardCallback ucb,
MulticastForwardCallback mcb, LocalDeliverCallback lcb,
ErrorCallback ecb) {
NS_LOG_FUNCTION(this << p << header << idev << ucb << mcb
<< lcb << ecb);
Ipv4Address dest = header.GetDestination();
if (dest == m_ipv4->GetAddress(1, 0).GetLocal()) {
lcb(p, header, idev);
return true;
}
if (m_routingTable.find(dest) == m_routingTable.end()) {
ecb(p, header, Socket::ERROR_NOROUTETOHOST);
return false;
}
Ptr<Ipv4Route> route = Create<Ipv4Route>();
route->SetDestination(dest);
route->SetGateway(m_routingTable[dest]);
route->SetOutputDevice(idev);
ucb(route, p, header);
return true;
}
void OspfRouting::NotifyInterfaceUp(uint32_t interface) {
NS_LOG_FUNCTION(this << interface);
Ptr<Socket> socket = Socket::CreateSocket(GetObject<Node>(), TypeId::LookupByName(“ns3::UdpSocketFactory”));
socket->SetAllowBroadcast(true);
socket->BindToNetDevice(m_ipv4->GetNetDevice(interface));
socket->Bind(InetSocketAddress(Ipv4Address::GetAny(), 80));
socket->SetRecvCallback(MakeCallback(&OspfRouting::ReceiveLinkStateAdvertisement, this));
m_socketMap[interface] = socket;
}
void OspfRouting::NotifyInterfaceDown(uint32_t interface) {
NS_LOG_FUNCTION(this << interface);
m_socketMap[interface]->Close();
m_socketMap.erase(interface);
}
void OspfRouting::NotifyAddAddress(uint32_t interface,
Ipv4InterfaceAddress address) {
NS_LOG_FUNCTION(this << interface << address);
}
void OspfRouting::NotifyRemoveAddress(uint32_t interface,
Ipv4InterfaceAddress address) {
NS_LOG_FUNCTION(this << interface << address);
}
}
Integrate the Custom Routing Protocol :
#include “ospf-routing.h”
int main(int argc, char *argv[]) {
CommandLine cmd;
cmd.Parse(argc, argv);
NodeContainer nodes;
nodes.Create(4);
PointToPointHelper pointToPoint;
pointToPoint.SetDeviceAttribute(“DataRate”, StringValue(“5Mbps”));
pointToPoint.SetChannelAttribute(“Delay”, StringValue(“2ms”));
NetDeviceContainer devices01 = pointToPoint.Install(nodes.Get(0), nodes.Get(1));
NetDeviceContainer devices12 = pointToPoint.Install(nodes.Get(1), nodes.Get(2));
NetDeviceContainer devices23 = pointToPoint.Install(nodes.Get(2), nodes.Get(3));
NetDeviceContainer devices30 = pointToPoint.Install(nodes.Get(3), nodes.Get(0));
InternetStackHelper stack;
OspfRoutingHelper ospfRouting;
Ipv4ListRoutingHelper list;
list.Add(ospfRouting, 0);
stack.SetRoutingHelper(list);
stack.Install(nodes);
Ipv4AddressHelper address;
address.SetBase(“10.1.1.0”, “255.255.255.0”);
address.Assign(devices01);
address.SetBase(“10.1.2.0”, “255.255.255.0”);
address.Assign(devices12);
address.SetBase(“10.1.3.0”, “255.255.255.0”);
address.Assign(devices23);
address.SetBase(“10.1.4.0”, “255.255.255.0”);
address.Assign(devices30);
// Set up applications
uint16_t port = 9;
UdpEchoServerHelper server(port);
ApplicationContainer apps = server.Install(nodes.Get(3));
apps.Start(Seconds(1.0));
apps.Stop(Seconds(10.0));
UdpEchoClientHelper client(address.GetAddress(3), port);
client.SetAttribute(“MaxPackets”, UintegerValue(1));
client.SetAttribute(“Interval”, TimeValue(Seconds(1.0)));
client.SetAttribute(“PacketSize”, UintegerValue(1024));
apps = client.Install(nodes.Get(0));
apps.Start(Seconds(2.0));
apps.Stop(Seconds(10.0));
Simulator::Run();
Simulator::Destroy();
return 0;
}
Explanation
- Network Topology :
The four nodes connected in a ring, to set up the network topology.
- OSPF Routing Protocol :
A custom OSPF-like routing protocol class (OspfRouting) is implemented for handling route computation and distribution on the basis of link-state advertisements and Dijkstra’s algorithm for shortest path calculation.
- Route Computation :
To compute the shortest paths based on the link-state database, the CalculateShortestPaths method implemented Dijkstra’s algorithm.
- Link State Advertisements :
The SendLinkStateAdvertisement method is used to send the current link-state database to neighbors, and the ReceiveLinkStateAdvertisement method is used to processe incoming link-state advertisements and update the link-state database.
- Route Input and Output :
To handle packet routing based on the routing table, the RouteInput and RouteOutput methods are used.
- Integrate Custom Routing Protocol :
The custom routing protocol is integrated into the ns3 stack using the OspfRoutingHelper.
- Applications :
To set up to test the routing, UdpEchoServer and UdpEchoClient applications are used.
Running the Code :
Save your script to a file, for example, ospf-routing.cc and Compile the script using the ns3 build system
./waf configure –enable-examples
./waf build
./waf –run scratch/ospf-routing
Overall, we had successfully learned on implementing OSPF (Open Shortest Path First) routing in ns3 which incorporates creating a custom routing protocol class that mimics the behavior of OSPF. OSPF (Open Shortest Path First) routing in ns3 is quiet high we grant best results, for your programming.