I have just installed a couple of 3910 routers at 2 sites. The to LANs have the same subnet so i have setup double-NAT as per the guide https://www.draytek.co.uk/support/guides/kb-vpn-samesubnet . That all appears to work fine and i can ping and transfer files with SMB etc using the spoofed subnet addresses.
The one thing that does not work is telnet sessions over the site-to-site VPN on the default port-23. I can't see any filter rules or blocks in place that would stop those telnet connections. Anyone have any ideas?
Thanks

never mind - i found the issue. nothing to do with the site-to-site VPN or Draytek firewall.