[Ns-developers] GlobalRoutingManager and virtual interfaces

[Tom Henderson]

Gustavo Carneiro wrote:
> 2008/5/14 Mathieu Lacage <mathieu.lacage at sophia.inria.fr>:
> 
>> On Wed, 2008-05-14 at 15:05 +0100, Gustavo Carneiro wrote:
>>> Hello, I am working on a VirtualNetDevice in ns-3.0.11, which is
>> something
>>> similar to Linux "tap" interfaces.
>>>
>>> GlobalRoutingManager::PopulateRoutingTables () is segfaulting or
>> aborting in
>>> this simulated network that I have.  Maybe someone can give me some
>> advice
>>> here.
>>>
>>> If I configure the virtual interface with EnableBroadcast() or
>>> EnablePointToPoint(), GlobalRoutingManager will assume the netdevice has
>> a
>>> channel and try to do something with it.  Obviously it doesn't have any
>>> channel, so GRM will just segfault.
>> Can't you just make your virtual device return a "virtual" channel which
>> implements the Channel API correctly ?
> 
> 
> I could, but on the other hand adapting GlobalRoutingManager to cope with
> with no-channel netdevice was trivial after all:
> 
> diff -r d39382729adb src/routing/global-routing/global-router-interface.cc
> --- a/src/routing/global-routing/global-router-interface.cc    Thu May 08
> 14:50:16 2008 +0100
> +++ b/src/routing/global-routing/global-router-interface.cc    Wed May 14
> 16:23:42 2008 +0100
> @@ -625,6 +640,10 @@ GlobalRouter::DiscoverLSAs (void)
>  // router (to use OSPF lingo) is running.
>  //
>            Ptr<Channel> ch = ndLocal->GetChannel();
> +          if (ch == NULL)
> +            {
> +              continue;
> +            }
>            Ptr<NetDevice> ndRemote = GetAdjacent(ndLocal, ch);
>  //
>  // The adjacent net device is aggregated to a node.  We need to ask that
> net
> 
> Would it be ok to commit the above patch instead?
> 
> I think this is a similar situation to the "Loopback" interface of IPv4,
> which has no associated NetDevice (it is NULL), when the alternative would
> be to provide a "dummy" NetDevice was not pursued.  So, I think this counts
> as prior art, in favor of my simpler solution. :-)
> 
> The other part, coping with non-IP NetDevices, has also been fixed in my
> tree, like this:
> 
> diff -r d39382729adb src/routing/global-routing/global-router-interface.cc
> --- a/src/routing/global-routing/global-router-interface.cc    Thu May 08
> 14:50:16 2008 +0100
> +++ b/src/routing/global-routing/global-router-interface.cc    Wed May 14
> 16:23:42 2008 +0100
> @@ -535,6 +535,21 @@ GlobalRouter::DiscoverLSAs (void)
>      {
>        Ptr<NetDevice> ndLocal = node->GetDevice(i);
> 
> +      // 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;
> +        }
> +
>        if (ndLocal->IsBroadcast () && !ndLocal->IsPointToPoint () )
>          {
>            NS_LOG_LOGIC ("Broadcast link");
> 
> 

I would be fine with both of your patches.  However, these still do not 
account for the case when there is an IP interface but the next hop at 
L2 is a L2 device such as a switch (see bug 114).  So, I am fine with 
your fixes for now but we still need to fix bug 114 too.

- Tom