6.5 Support for multiple routing protocols

Typically, multiple routing protocols are supported in user space and coordinate to write a single forwarding table in the kernel. Presently in ns-3, the implementation allows for multiple routing protocols to build/keep their own routing state, and the IPv4 implementation will query each one of these routing protocols (in some order determined by the simulation author) until a route is found. This may better faciliate the integration of disparate routing approaches that may be difficult to coordinate the writing to a single table, approaches where more information than destination IP address (e.g., source routing) is used to determine the next hop, and on-demand routing approaches where packets must be cached.

There are presently two routing protocols defined:

• class Ipv4StaticRouting (covering both unicast and multicast)
• Optimized Link State Routing (a MANET protocol defined in RFC 3626)

void
Ipv4L3Protocol::Lookup (
  uint32_t ifIndex,
  Ipv4Header const &ipHeader,
  Packet packet,
  Ipv4RoutingProtocol::RouteReplyCallback routeReply)
{
  NS_LOG_FUNCTION;
  NS_LOG_PARAM ("(" << ifIndex << ", " << &ipHeader << ", " << &packet <<
    &routeReply << ")");

  for (Ipv4RoutingProtocolList::const_iterator rprotoIter =
         m_routingProtocols.begin ();
       rprotoIter != m_routingProtocols.end ();
       rprotoIter++)
    {
      NS_LOG_LOGIC ("Requesting route");
      if ((*rprotoIter).second->RequestRoute (ifIndex, ipHeader, packet,
                                              routeReply))
        return;
    }

  if (ipHeader.GetDestination ().IsMulticast () &&
      ifIndex == Ipv4RoutingProtocol::IF_INDEX_ANY)
    {
      NS_LOG_LOGIC ("Multicast destination with local source");

Ipv4L3Protocol::Lookup (Ipv4Header const &ipHeader,
                        Packet packet,
                        pv4Route *route = m_staticRouting->GetDefaultRoute ();

      if (route)
        {
          NS_LOG_LOGIC ("Local source. Using unicast default route for "
            "multicast packet");

          routeReply (true, *route, packet, ipHeader);
          return;
        }
    }
//
// No route found
//
  routeReply (false, Ipv4Route (), packet, ipHeader);
}