diff --git a/etc/sysctl.d/tcp_hardening.conf b/etc/sysctl.d/tcp_hardening.conf
index 7174c2d..85b6ddf 100644
--- a/etc/sysctl.d/tcp_hardening.conf
+++ b/etc/sysctl.d/tcp_hardening.conf
@@ -35,6 +35,7 @@ net.ipv4.conf.default.accept_source_route=0
 
 ## Enable reverse path filtering to prevent IP spoofing and
 ## mitigate vulnerabilities such as CVE-2019-14899.
+## https://forums.whonix.org/t/enable-reverse-path-filtering/8594
 net.ipv4.conf.default.rp_filter=1
 net.ipv4.conf.all.rp_filter=1