/etc/default/ufw
IPV6=yes
DEFAULT_INPUT_POLICY="DROP"
DEFAULT_OUTPUT_POLICY="DROP"
DEFAULT_FORWARD_POLICY="DROP"
DEFAULT_APPLICATION_POLICY="SKIP"
MANAGE_BUILTINS=no
IPT_SYSCTL=/etc/ufw/sysctl.conf
IPT_MODULES="nf_conntrack_ftp nf_nat_ftp nf_conntrack_netbios_ns"

/etc/ufw/sysctl.conf
net/ipv4/conf/default/rp_filter=1
net/ipv4/conf/all/rp_filter=1
net/ipv4/conf/default/accept_source_route=0
net/ipv4/conf/all/accept_source_route=0
net/ipv6/conf/default/accept_source_route=0
net/ipv6/conf/all/accept_source_route=0
net/ipv4/conf/default/accept_redirects=0
net/ipv4/conf/all/accept_redirects=0
net/ipv6/conf/default/accept_redirects=0
net/ipv6/conf/all/accept_redirects=0
net/ipv4/icmp_echo_ignore_broadcasts=1
net/ipv4/icmp_ignore_bogus_error_responses=1
net/ipv4/icmp_echo_ignore_all=0
net/ipv4/conf/default/log_martians=0
net/ipv4/conf/all/log_martians=0
net/ipv4/tcp_sack=1