@ -28,6 +28,7 @@
## :ballot_box_with_check: TODO
- [ ] Add useful Iptables configuration examples
- [x] Add useful Kernel Settings (sysctl) configuration
- [ ] Add links to useful external resources
- [ ] Add advanced configuration examples, commands, rules
@ -38,6 +39,14 @@
- [Tools to help you configure Iptables ](#tools-to-help-you-configure-iptables )
- [Manuals/Howtos/Tutorials ](#manualshowtostutorials )
- [Useful Kernel Settings (sysctl) configuration ](#useful-kernel-settings-sysctl-configuration )
* [rp_filter ](#rp_filter )
* [log_martians ](#log_martians )
* [send_redirects ](#send_redirects )
* [accept_source_route ](#accept_source_route )
* [accept_redirects ](#accept_redirects )
* [tcp_syncookies ](#tcp_syncookies )
* [icmp_echo_ignore_broadcasts ](#icmp_echo_ignore_broadcasts )
* [ip_forward ](#ip_forward )
- [How it works? ](#how-it-works )
- [Iptables Rules ](#iptables-rules )
* [Saving Rules ](#saving-rules )
@ -131,70 +140,112 @@
### Useful Kernel Settings (sysctl) Configuration
```bash
cat < < EOF > /etc/sysctl.d/40-custom.conf
##### rp_filter
#---------------------------------------------------------------
# Disable routing triangulation. Respond to queries out
# the same interface, not another. Helps to maintain state
# Also protects against IP spoofing
#---------------------------------------------------------------
> _Disable routing triangulation. Respond to queries out the same interface, not another. Also protects against IP spoofing._
```bash
cat < < EOF > > /etc/sysctl.d/40-custom.conf
net/ipv4/conf/all/rp_filter = 1
EOF
```
- [rp_filter and LPIC-3 Linux Security ](https://www.theurbanpenguin.com/rp_filter-and-lpic-3-linux-security/ )
- [Linux kernel rp_filter settings (Reverse path filtering) ](https://www.slashroot.in/linux-kernel-rpfilter-settings-reverse-path-filtering )
- [Reverse Path Filtering ](http://tldp.org/HOWTO/Adv-Routing-HOWTO/lartc.kernel.rpf.html )
#---------------------------------------------------------------
# Enable logging of packets with malformed IP addresses
#---------------------------------------------------------------
##### log_martians
> _Enable logging of packets with malformed IP addresses._
```bash
cat < < EOF > > /etc/sysctl.d/40-custom.conf
net/ipv4/conf/all/log_martians = 1
EOF
```
- [What is the usefulness of logging of martians packet? ](https://serverfault.com/questions/570980/what-is-the-usefulness-of-logging-of-martians-packet-e-g-net-ipv4-conf-all-lo )
#---------------------------------------------------------------
# Disable redirects
#---------------------------------------------------------------
##### send_redirects
> _Disables sending of all IPv4 ICMP redirected packets on all interfaces._
```bash
cat < < EOF > > /etc/sysctl.d/40-custom.conf
net/ipv4/conf/all/send_redirects = 0
EOF
```
- [Disable source routing ](https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/security_guide/sect-security_guide-server_security-disable-source-routing )
- [What are ICMP redirects and should they be blocked? ](https://askubuntu.com/questions/118273/what-are-icmp-redirects-and-should-they-be-blocked )
#---------------------------------------------------------------
# Disable source routed packets
#---------------------------------------------------------------
##### accept_source_route
> _Disable source routed packets (packets with the Strict Source Route (SSR) or Loose Source Routing (LSR) option set)._
```bash
cat < < EOF > > /etc/sysctl.d/40-custom.conf
net/ipv4/conf/all/accept_source_route = 0
EOF
```
- [Disable source routing ](https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/security_guide/sect-security_guide-server_security-disable-source-routing )
- [The system must not accept IPv4 source-routed packets by default. ](https://www.stigviewer.com/stig/red_hat_enterprise_linux_6/2017-12-08/finding/V-38529 )
#---------------------------------------------------------------
# Disable acceptance of ICMP redirects
#---------------------------------------------------------------
##### accept_redirects
> _Disable acceptance of ICMP redirects._
```bash
cat < < EOF > > /etc/sysctl.d/40-custom.conf
net/ipv4/conf/all/accept_redirects = 0
EOF
```
- [What are ICMP redirects and should they be blocked? ](https://askubuntu.com/questions/118273/what-are-icmp-redirects-and-should-they-be-blocked )
- [The Red Hat Enterprise Linux operating system must ignore Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirect messages. ](https://www.stigviewer.com/stig/red_hat_enterprise_linux_7/2018-11-28/finding/V-73175 )
#---------------------------------------------------------------
# Turn on protection from Denial of Service (DOS) attacks
#---------------------------------------------------------------
##### tcp_syncookies
> _Turn on SYN-flood protections (protection from Denial of Service (DOS) attacks)._
```bash
cat < < EOF > > /etc/sysctl.d/40-custom.conf
net/ipv4/tcp_syncookies = 1
EOF
```
- [Hardening your TCP/IP Stack Against SYN Floods ](https://www.ndchost.com/wiki/server-administration/hardening-tcpip-syn-flood )
- [Linux: Turn On TCP SYN Cookie Protection ](https://www.cyberciti.biz/faq/enable-tcp-syn-cookie-protection/ )
- [Better alternative for tcp_syncookies in Linux ](https://serverfault.com/questions/705504/better-alternative-for-tcp-syncookies-in-linux )
#---------------------------------------------------------------
# Disable responding to ping broadcasts
#---------------------------------------------------------------
##### icmp_echo_ignore_broadcasts
> _Disable responding to ping broadcasts._
```bash
cat < < EOF > > /etc/sysctl.d/40-custom.conf
net/ipv4/icmp_echo_ignore_broadcasts = 1
EOF
```
- [What is ICMP broadcast good for? ](https://superuser.com/questions/306065/what-is-icmp-broadcast-good-for )
- [The system must not respond to ICMPv4 sent to a broadcast address. ](https://www.stigviewer.com/stig/red_hat_enterprise_linux_6/2018-11-28/finding/V-38535 )
#---------------------------------------------------------------
# Enable IP routing. Required if your firewall is protecting a
# network, NAT included
#---------------------------------------------------------------
##### ip_forward
net/ipv4/ip_forward = 1
> _Enable IP routing. Required if your firewall is protecting a network, NAT included._
```bash
cat < < EOF > > /etc/sysctl.d/40-custom.conf
net/ipv4/ip_forward = 1
EOF
```
- [Introduction to routers ](http://linux-training.be/security/ch10.html )
- [How to Enable IP Forwarding in Linux ](http://www.ducea.com/2006/08/01/how-to-enable-ip-forwarding-in-linux/ )
- [What is kernel ip forwarding? ](https://unix.stackexchange.com/questions/14056/what-is-kernel-ip-forwarding )
### How it works?
< p align = "center" >