LAN - where is the invisible node created

[anandr@cs.ucsb.edu (Anand P. Rangarajan)]

hi

  i'm printing the next hop information for some 
  topologies.

  if all the links in the network were just 
  point-to-point links
  the table has exactly the same number of nodes
  as in the topology. but if there is a LAN, there
  seems to be another node which connects the nodes
  in the LAN and the other part of the topology.

Example:

Topology:
  
   3
   |
   |
 -----
   |
   |
   1-------2-------0


In the above topology, 3 is the only node in the LAN 
and 1 is the router between the LAN and the other part
of the network.


Dumpingng Routing Table: Next Hop Information
        0       1       2       3       4
0       --      2       2       2       2
1       2       --      2       4       4
2       0       1       --      1       1
3       4       4       4       --      4
4       1       1       1       3       --
 

one can see a new node "4" in the table that connects 3 
and 1.

  i wish to know where( in the ns source code) and 
  why this new node is created.

  i'd appreciate if someone throws light on this.


Thanks,
Anand