examples: Adding new example to illustrate use of L2Tracer to trace aggregate packet drop rate on nodes
diff --git a/examples/topologies/topo-tree-25-node.txt b/examples/topologies/topo-tree-25-node.txt
new file mode 100644
index 0000000..7b328f4
--- /dev/null
+++ b/examples/topologies/topo-tree-25-node.txt
@@ -0,0 +1,58 @@
+#Topology.Scenario3.txt
+
+router
+
+# node comment yPos xPos
+Rtr1 NA 3 9
+Rtr2 NA 9 9
+Rtr3 NA 15 9
+Rtr7 NA 9 15
+Rtr4 NA 3 21
+Rtr5 NA 9 21
+Rtr6 NA 15 21
+Src1 NA 1 3
+Src2 NA 3 3
+Src3 NA 5 3
+Src4 NA 7 3
+Src5 NA 9 3
+Src6 NA 11 3
+Src7 NA 13 3
+Src8 NA 15 3
+Src9 NA 17 3
+Dst1 NA 1 27
+Dst2 NA 3 27
+Dst3 NA 5 27
+Dst4 NA 7 27
+Dst5 NA 9 27
+Dst6 NA 11 27
+Dst7 NA 13 27
+Dst8 NA 15 27
+Dst9 NA 17 27
+
+link
+# srcNode dstNode bandwidth metric delay queue
+Src1 Rtr1 100Mbps 1 10ms 10
+Src2 Rtr1 100Mbps 1 10ms 10
+Src3 Rtr1 100Mbps 1 10ms 10
+Src4 Rtr2 100Mbps 1 10ms 10
+Src5 Rtr2 100Mbps 1 10ms 10
+Src6 Rtr2 100Mbps 1 10ms 10
+Src7 Rtr3 100Mbps 1 10ms 10
+Src8 Rtr3 100Mbps 1 10ms 10
+Src9 Rtr3 100Mbps 1 10ms 10
+Rtr1 Rtr7 10Mbps 1 10ms 10
+Rtr2 Rtr7 10Mbps 1 10ms 10
+Rtr3 Rtr7 10Mbps 1 10ms 10
+Rtr4 Rtr7 10Mbps 1 10ms 10
+Rtr5 Rtr7 10Mbps 1 10ms 10
+Rtr6 Rtr7 10Mbps 1 10ms 10
+Dst1 Rtr4 100Mbps 1 10ms 10
+Dst2 Rtr4 100Mbps 1 10ms 10
+Dst3 Rtr4 100Mbps 1 10ms 10
+Dst4 Rtr5 100Mbps 1 10ms 10
+Dst5 Rtr5 100Mbps 1 10ms 10
+Dst6 Rtr5 100Mbps 1 10ms 10
+Dst7 Rtr6 100Mbps 1 10ms 10
+Dst8 Rtr6 100Mbps 1 10ms 10
+Dst9 Rtr6 100Mbps 1 10ms 10
+