How to Begin Implement ECMP Routing in NS3

To implement an Equal-Cost Multi-Path (ECMP) routing utilising NS3 which needs to design a routing protocol or prolong an existing one that allowing several next-hop routes with the same amount of cost for destinations. ECMP supports packets to be delivered through numerous routes to enhance the network deployment and fault tolerance.

Here’s a guide on how to execute the ECMP Routing using NS3:

Steps to Begin Implement ECMP Routing in NS3

Step 1: Understand ECMP

1. Key Features:
   • Multiple Paths: ECMP facilitates many next-hop routes for a single destination.
   • Load Balancing: Traffic can divide through the routes which is frequently utilising the hashing at packet headers such as IP or transport-layer fields.
   • Fault Tolerance: It offers redundancy if one path is failure.
2. Applications:
   • Internet Service Provider (ISP) networks.
   • Data center networks.
   • Traffic engineering within SDN environments.

Step 2: Set Up NS3 Environment

1. Create a Protocol Directory:
   • Make a new protocol directory in src/, for instance src/ecmp-routing/.
2. Add Required Files:
   • ecmp-routing-helper.h and ecmp-routing-helper.cc: Helper classes.
   • ecmp-routing-protocol.h: Header file for ECMP routing.
   • ecmp-routing-protocol.cc: Execution file.
3. Update Build System:
   • Change the wscript in src/ with the new component for modernizing the system.

Step 3: Design ECMP Protocol

Define the Protocol Class

For prolonging the Ipv4RoutingProtocol class, we will need to execute the functionality of ECMP.

Header File (ecmp-routing-protocol.h)

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

#include “ns3/socket.h”

#include <map>

#include <vector>

class EcmpRoutingProtocol : public ns3::Ipv4RoutingProtocol {

public:

static ns3::TypeId GetTypeId (void);

EcmpRoutingProtocol ();

virtual ~EcmpRoutingProtocol ();

// 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 AddRoute (ns3::Ipv4Address destination, std::vector<ns3::Ipv4Address> nextHops, uint32_t interface);

private:

struct EcmpRouteEntry {

std::vector<ns3::Ipv4Address> nextHops;

uint32_t interface;

};

std::map<ns3::Ipv4Address, EcmpRouteEntry> m_routingTable; // Destination -> ECMP routes

};

Implement Core Functions

Add Routes with Multiple Next Hops

Enable integrating the paths including numerous next-hop choices.

void EcmpRoutingProtocol::AddRoute (ns3::Ipv4Address destination, std::vector<ns3::Ipv4Address> nextHops, uint32_t interface) {

EcmpRouteEntry entry = {nextHops, interface};

m_routingTable[destination] = entry;

}

Select a Next Hop for Outgoing Packets

Execute a load-balancing mechanism like hashing at packet headers or round-robin.

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

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

const ns3::Ipv4Header &header,

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

ns3::Socket::SocketErrno &sockerr) {

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

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

// Example: Hash-based selection

uint32_t hash = header.GetSource().Get() ^ header.GetDestination().Get();

uint32_t index = hash % it->second.nextHops.size();

ns3::Ipv4Address nextHop = it->second.nextHops[index];

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

route->SetGateway(nextHop);

route->SetOutputDevice(oif);

return route;

}

sockerr = ns3::Socket::ERROR_NOROUTETOHOST;

return nullptr;

}

Forward Incoming Packets

Leverage the routing table, we can transmit the incoming packets.

bool EcmpRoutingProtocol::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) {

if (header.GetDestination() == m_selfAddress) {

lcb(packet, header, 0); // Deliver locally

return true;

}

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

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

// Select a next hop

uint32_t hash = header.GetSource().Get() ^ header.GetDestination().Get();

uint32_t index = hash % it->second.nextHops.size();

ns3::Ipv4Address nextHop = it->second.nextHops[index];

ucb(packet, header, nextHop, it->second.interface);

return true;

}

ecb(packet, header, ns3::Ipv4Header::DESTINATION_UNREACHABLE);

return false;

}

Step 4: Write a Helper Class

Make a helper class to make simpler ECMP incorporation using ECMP routing protocol.

#include “ecmp-routing-protocol.h”

class EcmpRoutingHelper {

public:

void Install (ns3::NodeContainer nodes) {

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

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

(*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 “ecmp-routing-helper.h”

using namespace ns3;

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

NodeContainer nodes;

nodes.Create (5);

InternetStackHelper stack;

stack.Install (nodes);

EcmpRoutingHelper ecmpHelper;

ecmpHelper.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(0), nodes.Get(2));

p2p.Install (nodes.Get(1), nodes.Get(3));

p2p.Install (nodes.Get(2), nodes.Get(3));

Ipv4AddressHelper ipv4;

ipv4.SetBase (“10.1.1.0”, “255.255.255.0”);

ipv4.Assign (p2p.GetNetDeviceContainer());

ns3::Ptr<EcmpRoutingProtocol> ecmp = nodes.Get(0)->GetObject<EcmpRoutingProtocol>();

ecmp->AddRoute(Ipv4Address(“10.1.1.3”), {Ipv4Address(“10.1.1.1”), Ipv4Address(“10.1.1.2”)}, 1);

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:
   • Make use of AsciiTraceHelper or PcapHelper for confirming the dividing traffic.
2. Enhancements:
   • Execute advanced load balancing mechanisms for route enhancements.
   • Integrate fault detection and active path elimination.

We have effectively demonstrated the detailed methodology on how to implement and analyze the ECMP Routing in NS3 simulator. More in-depth information can be provided upon request.