The UDP part your're seeing is seperate from the router.
To break it down
Router (Dynamips) <-> UDP Tunnel <-> VBox Guest
So as you say the UDP Tunnel is simply to create a network cable. The router doesn't know anything about this, it just has it's interfaces. In the example posted, have you tried using a basic Ethernet Switch in GNS3 in the middle?
I have used this method before with great success... even configuring VLANs.
I've been having nothing but troubles getting a guest VM to talk to my routers, even with either a swouter or etherswitch. I've tried host-only, internal network, and bridged, and I just can't get the VM to ping anything. Is there a walkthrough video or something? I've tried following the Virtualbox and GNS3 books from Packt, but the only thing that works is direct connecting with UDP TunnelingHere's the sample topology I'm trying
It's a 2008R2 serving running PRTG for SYSLOG, SNMP, and Netflow stats/graphing. That directly connected to a plain switch, along with C1 (with multiple connections to simulate many hosts), 2 2610XM routers (for HSRP/VRRP/GLBP, OSPF, and EIGRP practice), a 36XX router to pretend to be two internet connections, and a host on the other end of R3 to test end-to-end connectivity.
I've tried this with every netowrking option I can think of, and I *still* can't get it to work. I need that 2008R2 server to be able to see and gather info from all the nodes in the topology.
What am I doing wrong? I've asked several times here already, but never got any response.