The third octet to 0 could be a solution. Back at the shop yesterday the other guy set up an ECS with the customer's database, including the 172.20.xx... addresses in the MBU and CCSU. I connected my laptop with a static IP in that range on our network. Was able to connect to the ECS which was connected to our network.

Several times did changes, like name, key pattern, etc. No errors at all - kept an eye on the ECS. What I should do - and have not yet, is to connect my laptop to LAN1 using the standard 172.30.30.30 address. (of course setting my laptop IP accordingly). Then again, if everything was working like this at the customer's site I wouldn't need to connect to LAN1 as long as I'm on their network.