From c34adc472c711358feccd760520fdb3602b2c1ff Mon Sep 17 00:00:00 2001
From: Kleissner <peter@kleissner.investments>
Date: Mon, 1 Mar 2021 04:13:18 +0100
Subject: [PATCH] Prevent link-local to non-link-local connections for
 multicast and broadcast.

---
 Network IPv4 Broadcast.go | 5 +++++
 Network IPv6 Multicast.go | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/Network IPv4 Broadcast.go b/Network IPv4 Broadcast.go
index bc48d54..946a1da 100644
--- a/Network IPv4 Broadcast.go	
+++ b/Network IPv4 Broadcast.go	
@@ -71,6 +71,11 @@ func (network *Network) BroadcastIPv4Listen() {
 			continue
 		}
 
+		// For good network practice (and reducing amount of parallel connections), do not allow link-local to talk to non-link-local addresses.
+		if sender.(*net.UDPAddr).IP.IsLinkLocalUnicast() != network.address.IP.IsLinkLocalUnicast() {
+			continue
+		}
+
 		//fmt.Printf("BroadcastIPv4Listen from %s at network %s\n", sender.String(), network.address.String())
 
 		if length < packetLengthMin {
diff --git a/Network IPv6 Multicast.go b/Network IPv6 Multicast.go
index eeae8e9..1437f37 100644
--- a/Network IPv6 Multicast.go	
+++ b/Network IPv6 Multicast.go	
@@ -117,6 +117,11 @@ func (network *Network) MulticastIPv6Listen() {
 			continue
 		}
 
+		// For good network practice (and reducing amount of parallel connections), do not allow link-local to talk to non-link-local addresses.
+		if sender.(*net.UDPAddr).IP.IsLinkLocalUnicast() != network.address.IP.IsLinkLocalUnicast() {
+			continue
+		}
+
 		//fmt.Printf("MulticastIPv6Listen from %s at network %s\n", sender.String(), network.address.String())
 
 		if length < packetLengthMin {