SQUID:
CVMFS on WorkerNodes uses IPv6 (configure flag: CVMFS_IPFAMILY_PREFER )
CVMFS frontier is still IPv4 even while both systems dual-stack, but if dual-stack is configured in case the IPv4 service is shut down it will smoothly switch over to IPv6
DNS:
- it is not enough that both (host and DNS server) are dual-stack configured
- /etc/resolve.conf does need the ipv6 address of the resolver