RFC 5128, seção 2.10 diz:
Hairpinning is defined in [BEH-UDP] as follows:
If two hosts (called X1 and X2) are behind the same NAT and exchanging traffic, the NAT may allocate an address on the outside of the NAT for X2, called X2':x2'. If X1 sends traffic to X2':x2', it goes to the NAT, which must relay the traffic from X1 to X2. This is referred to as hairpinning.
Not all currently deployed NATs support hairpinning.
Seu roteador simplesmente não suporta hairpinning. Tente conectar-se ao servidor de fora do NAT.