[Ns-developers] NetDevice and ArpIpv4Interface

[Mathieu Lacage]

On Thu, 2008-05-15 at 11:20 +0100, Gustavo Carneiro wrote:
> NetDevice and ArpIpv4Interface look perfect candidates for merging into a
> single virtual object via AddObject (aka AddInterface).  Right now:
> 
>   1- ArpIpv4Interface "decorates" (or "wraps") NetDevice;
>   2- The ArpIpv4Interface has one "interface index" at IP level, NetDevice
> has another "interface index" at Node level, and they can be different (I
> was surprised to find out recently);

Yes, because it is possible to have multiple Ipv4 interfaces to map to a
single NetDevice to support multihoming.

>   3- There are two interface lists, one at IP level, one at Node level;

Yes, again, this is by design to support multihoming.

>   4- Checking if a NetDevice supports IP or not is not trivial, as my
> GlobalRoutingManager patch demonstrates:
> 
> +      // Check if it is an IP interface (could be a pure L2 NetDevice)
> +      bool isIp = false;
> +      for (uint32_t i = 0; i < ipv4Local->GetNInterfaces (); ++i )
> +        {
> +          if (ipv4Local->GetNetDevice (i) == ndLocal)
> +            {
> +              isIp = true;
> +              break;
> +            }
> +        }
> +      if (!isIp)
> +        {
> +          continue;
> +        }
> +
> 
> I think this design predates the introduction of object interfaces in NS-3.
> If we were designing it now, I think most of us would agree in a better
> design:
> 
>   1- ArpIpv4Interface becomes an optional interface of NetDevice
> (AddObject);
>   2- Thus there would be only one interface index for both, and only one
> interface list at Node level (IP can filter out non-IP interfaces).

I don't think that the above could be made to support IP-level
multihoming correctly.

regards,
Mathieu