[Ns-developers] GlobalRoutingManager and virtual interfaces

[Gustavo Carneiro]

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");


-- 
Gustavo J. A. M. Carneiro
INESC Porto, Telecommunications and Multimedia Unit
"The universe is always one step beyond logic." -- Frank Herbert