Hi Fernando, NTP sounds simple but it could be very complex when you dig deep down and/or get lost in details. Here are 2 things to consider: 1. NTP clients can query NTP servers by using SRC UDP ports > 1024. 2. NTP servers cannot query/sync/communicate to another NTP server when using SRC UDP port > 1024. In short, server to server wants SRC and DST UDP 123. The query and the response will be fully 123 when server to server. In your case, it sounds like you want to achieve NTP server to NTP server, but you mention NTP clients behind NAT devices. Because multiple clients behind the same NAT devices should work. Multiple NTP servers behind the same NAT and wanting to use other NTP server *should* not work. Can you give us more details on what kind of communication you need here? From what I understand client to server should work just fine with any NAT devices. Maybe you meant multiple NTP servers behind the same NAT to external NTP server? Thanks Jean