I’ve been playing with Dynamips/GNS3 quite a bit lately. My current topology has 16 routers, some serving as Frame Relay routers, other as SP backbone routers, and others as switches via the NM-16ESW module. I found it easier to logically separate the connections to routers from the connections to other switches by using two EtherSwitch modules. I used the first one (Fa1/0 – 15) to connect to routers, and the second one (Fa2/0 – 15) to connect to the other switches. For some reason, I could never get the switches to talk to each other.