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Fix /net_restart and IPv6 multicast bugs #2002

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Fix /net_restart and IPv6 multicast bugs #2002

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62d6443
Set outgoing multicast interface for IPv6 LAN discovery
slipher Jun 11, 2026
58b9629
Comment about IPv6 multicast address
slipher Jun 14, 2026
c1f04d7
Log index parsed from net_mcast6iface
slipher Jun 11, 2026
6afb97b
Fix /net_restart on *nix with running server
slipher Sep 29, 2026
94fb3e3
Fix IP6 multicast receiving after /net_restart
slipher Sep 30, 2026
91d058a
Don't try to bind to IPv6 multicast address
slipher Sep 30, 2026
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49 changes: 28 additions & 21 deletions src/engine/qcommon/net_ip.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -88,6 +88,7 @@ static bool winsockInitialized = false;
# endif

# include <arpa/inet.h>
# include <fcntl.h>
# include <netdb.h>
# include <netinet/in.h>
# include <sys/socket.h>
Expand Down Expand Up @@ -149,6 +150,7 @@ static SOCKET socks_socket = INVALID_SOCKET;
static SOCKET multicast6_socket = INVALID_SOCKET;

// Keep track of currently joined multicast group.
// Also stores the multicast address info for clients though they don't join a group
static struct ipv6_mreq curgroup;

// And the currently bound address.
Expand All @@ -159,6 +161,10 @@ static struct sockaddr_in6 boundto;
#endif

// use an admin local address per default so that network admins can decide on how to handle quake3 traffic.
// However, an admin-local address usually doesn't go anywhere besides without special network
// configuration. Could use ff02 instead of ff04 meaning a link-local address more like IPv4, but
// then it doesn't work without manually setting net_mcast6iface.
// The final 4 quartets spell "ioquake3". TODO change for Daemon?
#define NET_MULTICAST_IP6 "ff04::696f:7175:616b:6533"

static const int MAX_IPS = 32;
Expand Down Expand Up @@ -946,6 +952,7 @@ SOCKET NET_IPSocket( const char *net_interface, int port, struct sockaddr_in *bi
newsocket = WSASocketW( PF_INET, SOCK_DGRAM, IPPROTO_UDP, nullptr, 0, WSA_FLAG_NO_HANDLE_INHERIT );
#else
newsocket = socket( PF_INET, SOCK_DGRAM, IPPROTO_UDP );
fcntl( newsocket, F_SETFD, FD_CLOEXEC );
#endif

if ( newsocket == INVALID_SOCKET )
Expand Down Expand Up @@ -1020,7 +1027,7 @@ SOCKET NET_IPSocket( const char *net_interface, int port, struct sockaddr_in *bi
NET_IP6Socket
====================
*/
SOCKET NET_IP6Socket( const char *net_interface, int port, struct sockaddr_in6 *bindto, int *err )
SOCKET NET_IP6Socket( const char *net_interface, int port, bool multicastSend, struct sockaddr_in6 *bindto, int *err )
{
SOCKET newsocket;
struct sockaddr_in6 address;
Expand All @@ -1037,6 +1044,7 @@ SOCKET NET_IP6Socket( const char *net_interface, int port, struct sockaddr_in6 *
newsocket = WSASocketW( PF_INET6, SOCK_DGRAM, IPPROTO_UDP, nullptr, 0, WSA_FLAG_NO_HANDLE_INHERIT );
#else
newsocket = socket( PF_INET6, SOCK_DGRAM, IPPROTO_UDP );
fcntl( newsocket, F_SETFD, FD_CLOEXEC );
#endif

if ( newsocket == INVALID_SOCKET )
Expand Down Expand Up @@ -1068,6 +1076,13 @@ SOCKET NET_IP6Socket( const char *net_interface, int port, struct sockaddr_in6 *
}
#endif

if ( multicastSend && curgroup.ipv6mr_interface && SOCKET_ERROR == setsockopt(
newsocket, IPPROTO_IPV6, IPV6_MULTICAST_IF, reinterpret_cast<const char *>( &curgroup.ipv6mr_interface ),
sizeof( curgroup.ipv6mr_interface ) ) )
{
Log::Warn( "NET_IP6Socket: couldn't set outbound multicast scope for socket: %s", NET_ErrorString() );
}

if ( !net_interface || !net_interface[ 0 ] )
{
memset( &address, 0, sizeof( address ) );
Expand Down Expand Up @@ -1140,6 +1155,7 @@ void NET_SetMulticast6()
curgroup.ipv6mr_interface = net_mcast6iface->integer;
#else
curgroup.ipv6mr_interface = if_nametoindex( net_mcast6iface->string );
Log::Notice( "Parsed IPv6 interface index: %d", curgroup.ipv6mr_interface );
#endif
}
else
Expand All @@ -1163,36 +1179,20 @@ void NET_JoinMulticast6()
return;
}

if ( IN6_IS_ADDR_MULTICAST( &boundto.sin6_addr ) || IN6_IS_ADDR_UNSPECIFIED( &boundto.sin6_addr ) )
if ( IN6_IS_ADDR_UNSPECIFIED( &boundto.sin6_addr ) )
{
// The way the socket was bound does not prohibit receiving multi-cast packets. So we don't need to open a new one.
multicast6_socket = ip6_socket;
}
else
{
if ( ( multicast6_socket = NET_IP6Socket( net_mcast6addr->string, ntohs( boundto.sin6_port ), nullptr, &err ) ) == INVALID_SOCKET )
if ( ( multicast6_socket = NET_IP6Socket( nullptr, ntohs( boundto.sin6_port ), false, nullptr, &err ) ) == INVALID_SOCKET )

@DolceTriade DolceTriade Oct 2, 2026

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Why nullptr now?

@slipher slipher Oct 2, 2026

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Don't try to bind to IPv6 multicast address

Internet sources say you are supposed to bind to the all-zeroes address
if you want to receive multicast packets, not the multicast address.
Indeed, when tested on Windows the attempt to bind to a multicast
address produced an error.

And null is treated as the all-zeroes address.

{
// If the OS does not support binding to multicast addresses, like Windows XP, at least try with a non-multicast socket.
multicast6_socket = ip6_socket;
}
}

if ( curgroup.ipv6mr_interface )
{
if ( setsockopt( multicast6_socket, IPPROTO_IPV6, IPV6_MULTICAST_IF,
( char * ) &curgroup.ipv6mr_interface, sizeof( curgroup.ipv6mr_interface ) ) < 0 )
{
Log::Notice( "NET_JoinMulticast6: Couldn't set scope on multicast socket: %s", NET_ErrorString() );

if ( multicast6_socket != ip6_socket )
{
closesocket( multicast6_socket );
multicast6_socket = INVALID_SOCKET;
return;
}
}
}

if ( setsockopt( multicast6_socket, IPPROTO_IPV6, IPV6_JOIN_GROUP, ( char * ) &curgroup, sizeof( curgroup ) ) )
{
Log::Notice( "NET_JoinMulticast6: Couldn't join multicast group: %s", NET_ErrorString() );
Expand Down Expand Up @@ -1246,6 +1246,7 @@ void NET_OpenSocks( int port )
socks_socket = WSASocketW( AF_INET, SOCK_STREAM, IPPROTO_TCP, nullptr, 0, WSA_FLAG_NO_HANDLE_INHERIT );
#else
socks_socket = socket( AF_INET, SOCK_STREAM, IPPROTO_TCP );
fcntl( socks_socket, F_SETFD, FD_CLOEXEC );
#endif

if ( socks_socket == INVALID_SOCKET )
Expand Down Expand Up @@ -1624,7 +1625,8 @@ static void NET_OpenIP( bool serverMode )
{
for ( i = ( port6 == PORT_ANY ? 1 : MAX_TRY_PORTS ); i; i-- )
{
ip6_socket = NET_IP6Socket( net_ip6->string, port6, &boundto, &err );
bool sendingMulticast = !serverMode && !( net_enabled->integer & NET_DISABLEMCAST );

@DolceTriade DolceTriade Oct 2, 2026

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Why conditional here?

@slipher slipher Oct 2, 2026

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Only the client can send multicast packets. This is supposed to be the equivalent of the IPv4 broadcast, to search for servers in a LAN. The server responds with a normal packet.

ip6_socket = NET_IP6Socket( net_ip6->string, port6, sendingMulticast, &boundto, &err );

if ( ip6_socket != INVALID_SOCKET )
{
Expand Down Expand Up @@ -1737,8 +1739,8 @@ void NET_EnableNetworking( bool serverMode )

networkingEnabled = true;

NET_SetMulticast6(); // just parses cvars
NET_OpenIP( serverMode );
NET_SetMulticast6();
SV_NET_Config();
}

Expand Down Expand Up @@ -1888,4 +1890,9 @@ void NET_Restart_f()
#else
NET_EnableNetworking( com_sv_running.Get() );
#endif

if ( com_sv_running.Get() )
{
NET_JoinMulticast6();
}
}
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