/etc/sysctl.d/11-gce-network-security.conf is in gce-compute-image-packages 20180129+dfsg1-0ubuntu3.
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 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 | # Copyright 2016 Google Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# Google-recommended kernel parameters
# 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
# Ignore source-routed packets
net.ipv4.conf.all.accept_source_route=0
net.ipv4.conf.default.accept_source_route=0
# Ignore ICMP redirects from non-GW hosts
net.ipv4.conf.all.accept_redirects=0
net.ipv4.conf.default.accept_redirects=0
net.ipv4.conf.all.secure_redirects=1
net.ipv4.conf.default.secure_redirects=1
# Don't pass traffic between networks or act as a router
net.ipv4.ip_forward=0
net.ipv4.conf.all.send_redirects=0
net.ipv4.conf.default.send_redirects=0
# Turn on Source Address Verification in all interfaces to
# prevent some spoofing attacks.
net.ipv4.conf.all.rp_filter=1
net.ipv4.conf.default.rp_filter=1
# Ignore ICMP broadcasts to avoid participating in Smurf attacks
net.ipv4.icmp_echo_ignore_broadcasts=1
# Ignore bad ICMP errors
net.ipv4.icmp_ignore_bogus_error_responses=1
# Log spoofed, source-routed, and redirect packets
net.ipv4.conf.all.log_martians=1
net.ipv4.conf.default.log_martians=1
# RFC 1337 fix
net.ipv4.tcp_rfc1337=1
# Addresses of mmap base, heap, stack and VDSO page are randomized
kernel.randomize_va_space=2
# Reboot the machine soon after a kernel panic.
kernel.panic=10
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