Pour éviter l'erreur ICMPv6: RA: ndisc_router_discovery failed to add default route
Correction, désactiver l’annonce des routes (accept_ra) :

nano /etc/sysctl.conf

# Uncomment the next line to enable packet forwarding for IPv6
#  Enabling this option disables Stateless Address Autoconfiguration
#  based on Router Advertisements for this host
net.ipv6.conf.all.forwarding=1

# Accept Router Advertisements
net.ipv6.conf.all.accept_ra=0

Activer net.ipv6.conf.all.forwarding=1 et ajouter net.ipv6.conf.all.accept_ra=0
Puis sysctl -p pour une validation immédiate