Hello, all: Can one agent at the same time join in two multicast groups? $node join-group $agent $group(1) $node join-group $agent $group(2) so that it can receive and send data to two groups at the same time. >From the source code : agent.h, node.h , ns-agent.tcl I can not find where node_ is defined as instance variable for class agent, while I noticed: $agent set node_ ... thank you. Sencun.