L2TP IPsec not working with a DDNS resolved IP address is odd, when the same IP address does work. But OpenVPN does have the configuration setting to allow or not using any or just a specific name (or if not a name then an IP address) as
@Telos asked.
Can you share the contents of your .ovpn file, with the private details obscured. e.g.
- AA.BB.CC.DD for an IP address
- my.ddns.domain.tld for a server name
- PP for port number
- and just remove the certificate information between the certificate tags.
openVPN file
PP for port number 1194
________________________________________
dev tun
tls-client
remote domip.synology.me 1194
# The "float" tells OpenVPN to accept authenticated packets from any address,
# not only the address which was specified in the --remote option.
# This is useful when you are connecting to a peer which holds a dynamic address
# such as a dial-in user or DHCP client.
# (Please refer to the manual of OpenVPN for more information.)
#float
# If redirect-gateway is enabled, the client will redirect it's
# default network gateway through the VPN.
# It means the VPN connection will firstly connect to the VPN Server
# and then to the internet.
# (Please refer to the manual of OpenVPN for more information.)
#redirect-gateway def1
# dhcp-option DNS: To set primary domain name server address.
# Repeat this option to set secondary DNS server addresses.
#dhcp-option DNS DNS_IP_ADDRESS
pull
# If you want to connect by Server's IPv6 address, you should use
# "proto udp6" in UDP mode or "proto tcp6-client" in TCP mode
proto udp
script-security 2
comp-lzo
reneg-sec 0
cipher AES-256-CBC
auth SHA512
auth-user-pass
<ca>