/etc/sysctl.d/10-network-security.conf is in procps 1:3.2.8-11ubuntu6.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 | # Turn on Source Address Verification in all interfaces to
# prevent some spoofing attacks.
net.ipv4.conf.default.rp_filter=1
net.ipv4.conf.all.rp_filter=1
# Turn on SYN-flood protections. Starting with 2.6.26, there is no loss
# of TCP functionality/features under normal conditions. When flood
# protections kick in under high unanswered-SYN load, the system
# should remain more stable, with a trade off of some loss of TCP
# functionality/features (e.g. TCP Window scaling).
net.ipv4.tcp_syncookies=1
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