question with multicast routing?

[Jun Wei <jun@CS.UCLA.EDU>]

On Fri, 15 Jan 1999, Haobo Yu wrote:

   > the 100 node topology from gt-itm/samples(ts100-3.gb). I use that
   > 100 nodes as routers, and attach 50 new nodes as end nodes to 50
   > routers "randomly". I set up DM tree, and tried to send multicast
   > traffic to 5 of the end notes. The only message I got was that
   > error message. I thought ns developer should know where that
   > message came from.

         >  _o4638: no target for slot 16384
   
   The message comes from one of the classifiers, which receives a packet
   with an address directing to an unknown "outgoing interface". However,
   many many reasons may cause this problem, including the agent sending out
   a bad packet, and this is a notoriously hard problem to solve. I'm no
   expert on this, so I guess you probably have to describe your problem in
   detail and send it to ns-users list. 
   
   > Anyway, I kind of suspect it was a routing problem.  The
   > ts100-3.gb has a square in the middle, meaning: 
   >  1---2
   >  |   |
   >  4---3
   > When I tried to draw multicast routing tree by hand, I found out
   > there are multiple paths from 1 to 3. I wonder if the routing in
   > ns disallow that. 
   
   ns supports that kind of topology. One of the script under tcl/ex has a
   triangle setting to test switching from one route to another in the
   presence of dynamics (link up/down).
   
   - Haobo

My question: there are two paths from 1 to 3 with the same
distance. When they both are up, which route will be chosen?
would that cause the above error message?


 Jun