TCP/IP don't care about the source MAC address. And destination MAC address is just used to make the packet end up at the right destination, without any other meaning to it. And the mapping between destination IP address and MAC address is solved by ARP. And several different IP addresses can use the same MAC address. Exactly how that MAC address looks like isn't an issue either. So, for TCP/IP, everything will work fine if you just use the actual MAC address the card have, even though you might be doing traffic both from the host, and from a simulator within the host. Reception is a bit worse, since you need to figure out if the received packet should go to the host or the simulator. DECnet works in a very different way, where each host *must* have a unique MAC address, and where the recipient really checks that the source MAC address is consistent with what was expected, or else the packet is dropped (yes, I'm writing and meaning source address here). And sending data is done to a specific MAC address without ARP. Instead the MAC address is calculated from the DECnet address, and is thus "known" already. For all hosts on the network. Believe me. You are not really seeing or understanding the problem yet, with the tests you are doing. Parts are things you need to read up on, on how DECnet works. And parts you'll only find out the hard way, as I did. :-) Johnny -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: bqt at softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol I see... yeah I have a VMS image, but really no idea how to setup it's networking... I 'used' VMS as a user ages ago, although it was mostly using EDT and fighting the gold key thing on terminals.... Anyways is there some online docs on setting up VMS's networking? I'd love to be able to dig deeper into this....