编辑/etc/sysconfig/network-scripts/ifcfg-eth0，添加

IPV6INIT=yes
IPV6ADDR=primary_ipv6_address/64
IPV6_DEFAULTGW=ipv6_gateway
IPV6_AUTOCONF=no
DNS1=2001:4860:4860::8844
DNS2=2001:4860:4860::8888
DNS3=209.244.0.3

测试

ping6 2001:4860:4860::8888

参考

https://www.digitalocean.com/community/tutorials/how-to-enable-ipv6-for-digitalocean-droplets