For Ubuntu:
net.ipv4.conf.all.send_redirects=0
net.ipv4.conf.default.send_redirects=0
net.ipv4.conf.all.secure_redirects=0
net.ipv4.conf.default.secure_redirects=0
net.ipv4.conf.all.log_martians=1
net.ipv4.conf.default.log_martians=1
net.ipv6.conf.all.accept_ra=0
net.ipv6.conf.default.accept_ra=0
# redundant parameters (defaults on Ubuntu 24.04 LTS)
net.ipv4.icmp_echo_ignore_broadcasts=1
net.ipv4.icmp_ignore_bogus_error_responses=1
net.ipv4.tcp_syncookies=1
net.ipv4.conf.all.accept_redirects=0
net.ipv4.conf.default.accept_redirects=0
net.ipv4.conf.all.accept_source_route=0
net.ipv6.conf.all.accept_source_route=0