@Sunshine thanks you for quick response! Sorry, but I can confirm that they are indeed the versions: MR400 v4.3, firmware 1.2.0 0.9.1 v 0001.0 build2205, rel.59424n and i need to link with MR600 v2,...

@MirkoA Hi, I have a MR400 v4.2. How can I downgrade? I need IPsec (as the version v2) to link to another router, the model is MR600 and has IPSec. thanks