Existen varias opciones para deshabilitar IPv6 en un equipo Linux, así que lo resumo y simplifico:
sed -i '/^::1/d' /etc/hosts
sed -i '/^ff0/d' /etc/hosts
cat >> /etc/sysctl.d/ipv6.conf << EOF
net.ipv6.conf.all.disable_ipv6=1
net.ipv6.conf.default.disable_ipv6=1
net.ipv6.conf.lo.disable_ipv6=1
EOF
cat >> /etc/sysconfig/network << EOF
NETWORKING_IPV6=no
IPV6_AUTOCONF=no
EOF
sed -i 's/IPV6INIT=yes/IPV6INIT=no/g' /etc/sysconfig/network-scripts/ifcfg-eth0
sed -i 's/IPV6_AUTOCONF=yes/IPV6_AUTOCONF=no/g' /etc/sysconfig/network-scripts/ifcfg-eth0
sed -i 's/IPV6_DEFROUTE=yes/IPV6_DEFROUTE=no/g' /etc/sysconfig/network-scripts/ifcfg-eth0
sed -i 's/IPV6_DISABLED=no/IPV6_DISABLED=yes/g' /etc/sysconfig/network-scripts/ifcfg-eth0
Es posible que si gestionamos la red via NetworkManager nos aparezcan las siguientes trazas en /var/log/messages:
Feb 4 19:37:05 node01 NetworkManager[718]: <warn> [1707075425.6232] ipv6ll[763149cc2844be78,ifindex=2]: changed: no IPv6 link local address to retry after Duplicate Address Detection failures (back off)
Feb 4 19:37:15 node01 NetworkManager[718]: <warn> [1707075435.6268] platform-linux: do-add-ip6-address[2: fe80::f03c:91ff:fe58:4a99]: failure 13 (Permission denied)
Feb 4 19:37:17 node01 NetworkManager[718]: <warn> [1707075437.6290] ipv6ll[763149cc2844be78,ifindex=2]: changed: no IPv6 link local address to retry after Duplicate Address Detection failures (back off)
Feb 4 19:37:27 node01 NetworkManager[718]: <warn> [1707075447.6379] platform-linux: do-add-ip6-address[2: fe80::f03c:91ff:fe58:4a99]: failure 13 (Permission denied)
Feb 4 19:37:29 node01 NetworkManager[718]: <warn> [1707075449.6401] ipv6ll[763149cc2844be78,ifindex=2]: changed: no IPv6 link local address to retry after Duplicate Address Detection failures (back off)
En cualquier caso, las podremos eliminar con los siguientes comandos:
nmcli con mod eth0 ipv6.method disabled
nmcli device modify eth0 ipv6.method disabled