Desculpe, meu erro de erro de digitação. Meu IPv4 público é: x.x.x.127, mas eu digitei:
ip tunnel add tun6to4 mode sit ttl 64 remote any local x.x.x.27
Agora, posso ping6 e traceroute6 para ipv6.google.com:
# ping6 -n -c 4 ipv6.google.com
PING ipv6.google.com(2404:6800:8005::63) 56 data bytes
64 bytes from 2404:6800:8005::63: icmp_seq=0 ttl=58 time=217 ms
64 bytes from 2404:6800:8005::63: icmp_seq=1 ttl=58 time=217 ms
64 bytes from 2404:6800:8005::63: icmp_seq=2 ttl=58 time=217 ms
64 bytes from 2404:6800:8005::63: icmp_seq=3 ttl=58 time=217 ms
--- ipv6.google.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3001ms
rtt min/avg/max/mdev = 217.258/217.366/217.489/0.577 ms, pipe 2
# traceroute6 ipv6.google.com
traceroute to ipv6.google.com (2404:6800:8005::63), 30 hops max, 40 byte packets
1 2002:c058:6301::1 (2002:c058:6301::1) 199.193 ms 199.169 ms 199.153 ms
2 gige-g4-12.core1.lax1.he.net (2001:470:0:14e::1) 199.279 ms 199.268 ms 199.403 ms
3 PR01.LAX03.google.com (2001:504:0:3:0:1:5169:1) 199.633 ms 199.620 ms 199.755 ms
4 2001:4860::1:0:991 (2001:4860::1:0:991) 242.128 ms 2001:4860::1:0:607 (2001:4860::1:0:607) 204.765 ms 2001:4860::1:0:991 (2001:4860::1:0:991) 204.753 ms
5 2001:4860::1:0:7ea (2001:4860::1:0:7ea) 235.740 ms 243.709 ms 2001:4860::1:0:21 (2001:4860::1:0:21) 233.959 ms
6 2001:4860::1:0:75 (2001:4860::1:0:75) 215.427 ms 233.980 ms 2001:4860::1:0:47 (2001:4860::1:0:47) 214.836 ms
7 2001:4860::1:0:1063 (2001:4860::1:0:1063) 242.264 ms 2001:4860::1:0:16 (2001:4860::1:0:16) 216.691 ms 2001:4860::1:0:1063 (2001:4860::1:0:1063) 242.287 ms
8 2001:4860::2:0:119c (2001:4860::2:0:119c) 217.665 ms 2001:4860::2:0:119b (2001:4860::2:0:119b) 217.597 ms 217.436 ms
9 * 2001:4860:0:1::e1 (2001:4860:0:1::e1) 221.650 ms *
10 2404:6800:8005::63 (2404:6800:8005::63) 216.882 ms 216.917 ms 216.897 ms
Vou tentar configurar o túnel 6in4 para ver o que é diferente do túnel 6to4.
Obrigado pela sua informação.