mdns broadcasting all interfaces while I want to bind only specified one

[eldereal]

I want my service bind only some interfaces. I can achieve it by:

swarm.listen_on(format!("/ip4/192.168.1.100/tcp/12345").parse()?)?;

By this, the service only listens on 192.168.1.100. But when I enable mdns service, It still broadcasting all interface addresses.

How to restrict mdns only specified addresses in such case? I think this should be a common issue, maybe I missed something. But I searched the document and sources and find no clues.

[dariusc93]

Hey @eldereal. I may be wrong, but reviewing the code it looks like this would likely require changing InterfaceState so it would use an explicit addresses instead of an unspecified address.

rust-libp2p/protocols/mdns/src/behaviour/iface.rs

Lines 121 to 154 in a2a2816

	let recv_socket = match addr {
	IpAddr::V4(addr) => {
	let socket = Socket::new(Domain::IPV4, Type::DGRAM, Some(socket2::Protocol::UDP))?;
	socket.set_reuse_address(true)?;
	#[cfg(unix)]
	socket.set_reuse_port(true)?;
	socket.bind(&SocketAddr::new(IpAddr::V4(Ipv4Addr::UNSPECIFIED), 5353).into())?;
	socket.set_multicast_loop_v4(true)?;
	socket.set_multicast_ttl_v4(255)?;
	socket.join_multicast_v4(&crate::IPV4_MDNS_MULTICAST_ADDRESS, &addr)?;
	U::from_std(UdpSocket::from(socket))?
	}
	IpAddr::V6(_) => {
	let socket = Socket::new(Domain::IPV6, Type::DGRAM, Some(socket2::Protocol::UDP))?;
	socket.set_reuse_address(true)?;
	#[cfg(unix)]
	socket.set_reuse_port(true)?;
	socket.bind(&SocketAddr::new(IpAddr::V6(Ipv6Addr::UNSPECIFIED), 5353).into())?;
	socket.set_multicast_loop_v6(true)?;
	// TODO: find interface matching addr.
	socket.join_multicast_v6(&crate::IPV6_MDNS_MULTICAST_ADDRESS, 0)?;
	U::from_std(UdpSocket::from(socket))?
	}
	};
	let bind_addr = match addr {
	IpAddr::V4(_) => SocketAddr::new(addr, 0),
	IpAddr::V6(_addr) => {
	// TODO: if-watch should return the scope_id of an address
	// as a workaround we bind to unspecified, which means that
	// this probably won't work when using multiple interfaces.
	// SocketAddr::V6(SocketAddrV6::new(addr, 0, 0, scope_id))
	SocketAddr::new(IpAddr::V6(Ipv6Addr::UNSPECIFIED), 0)
	}
	};

Any reason why you would like to use a specific address?

[eldereal]

Thank you @dariusc93 for your reply. My case is the server has two interfaces. One is public and one is private. I want peers only works in private network and do not expose data to public network. I will have a try to rewrite this code.

[drHuangMHT]

My idea would be exposing attack surface as little as possible. I'm also looking forward to this change!