Adds iptables known-issue

content/k3s/latest/en/known-issues/_index.md

@@ -7,3 +7,7 @@ The Known Issues are updated periodically and designed to inform you about any i
 **Snap Docker**
 
 If you plan to use k3s with docker, Docker installed via a snap package is not recommended as it has been known to cause issues running k3s.
+
+**Iptables**
+
+If you are running iptables in nftables mode instead of legacy you might encounter issues. We recommend utilizing newer iptables (such as 1.6.1+) to avoid issues.