VPN cannot resolve host address

[edrobal]

Hello.
I'm trying to configure a VPN connection for a W52P. Voip server has a dynamic IP so the remote address is xxxxx.dyndns.biz and the VPN cannot resolve host address. Why phone don't receive dns server from DHCP ?
<29>Apr 19 00:00:08 openvpn[910]: OpenVPN 2.2.1 arm-linux [SSL] [LZO2] [EPOLL] built on Nov 24 2015
<28>Apr 19 00:00:08 openvpn[910]: NOTE: OpenVPN 2.1 requires '--script-security 2' or higher to call user-defined scripts or executables
<29>Apr 19 00:00:08 openvpn[910]: Control Channel Authentication: using '/config/openvpn/keys/ta.key' as a OpenVPN static key file
<29>Apr 19 00:00:08 openvpn[910]: Outgoing Control Channel Authentication: Using 160 bit message hash 'SHA1' for HMAC authentication
<29>Apr 19 00:00:08 openvpn[910]: Incoming Control Channel Authentication: Using 160 bit message hash 'SHA1' for HMAC authentication
<29>Apr 19 00:00:08 openvpn[910]: Control Channel MTU parms [ L:1557 D:166 EF:66 EB:0 ET:0 EL:0 ]
<29>Apr 19 00:00:09 openvpn[910]: Socket Buffers: R=[110592->200000] S=[110592->200000]
<27>Apr 19 00:00:09 openvpn[910]: RESOLVE: Cannot resolve host address: cocktail.dyndns.biz: [HOST_NOT_FOUND] The specified host is unknown.
<29>Apr 19 00:00:09 openvpn[910]: Data Channel MTU parms [ L:1557 D:1450 EF:57 EB:4 ET:0 EL:0 ]
<29>Apr 19 00:00:09 openvpn[910]: Local Options hash (VER=V4): 'ed844052'
<29>Apr 19 00:00:09 openvpn[910]: Expected Remote Options hash (VER=V4): '8a244582'
<27>Apr 19 00:00:09 openvpn[952]: RESOLVE: Cannot resolve host address: cocktail.dyndns.biz: [HOST_NOT_FOUND] The specified host is unknown.

I capture ip trafic and wireshark doesn't show any dns request. Strange.