Виды и особенности протоклов подключения и топологий:
https://arctech.ru/info/sistemnoe_administrirovanie/sistemnoe_administrirovanie/systemnoe_administrirovanie_unix/linux_servery_v_korporativnoj_seti/openvpn_udp_vs_tcp_bridge_vs_p2p_net30_vs_subnet/
Problems with MTU in logs like “Bad encapsulated packet length from peer (20559), which must be > 0 and <= 1626” might be mitigated sometimes by adding this commands in “Advanced” field on the Server configuration page:
For TCP server use mssfix;
Tor UDP server use fragment XXXX; where XXXX is desired MTU value
Fix bad speed with help of MTU tuning:
https://www.thegeekpub.com/271035/openvpn-mtu-finding-the-correct-settings/
tun-mtu 1450; mssfix 1410;
Как настроить автоматическое включение VPN на iPhone: