From d8a9812adc0c5b4accc12cd7d1d16efba02af1aa Mon Sep 17 00:00:00 2001
From: sebres <serg.brester@sebres.de>
Date: Mon, 9 Jan 2023 16:21:36 +0100
Subject: [PATCH] improve auto detection of IPv6 - try to check sysctl
 net.ipv6.conf.all.disable_ipv6 (prefer value read from
 `/proc/sys/net/ipv6/conf/all/disable_ipv6`)

---
 fail2ban/server/ipdns.py | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fail2ban/server/ipdns.py b/fail2ban/server/ipdns.py
index 68757c25..aca0f6a6 100644
--- a/fail2ban/server/ipdns.py
+++ b/fail2ban/server/ipdns.py
@@ -212,6 +212,13 @@ class DNSUtils:
 	def _IPv6IsSupportedBySystem():
 		if not socket.has_ipv6:
 			return False
+		# try to check sysctl net.ipv6.conf.all.disable_ipv6:
+		try:
+			with open('/proc/sys/net/ipv6/conf/all/disable_ipv6', 'rb') as f:
+				# if 1 - disabled, 0 - enabled
+				return not int(f.read())
+		except:
+			pass
 		s = None
 		try:
 			# try to create INET6 socket: