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socket.connect does not use specified localAddress for DNS lookup #14617
Description
Version: 8.2.1
Platform: Windows 10, x64
Subsystem: DNS / Net
I am establishing a TCP connection to a remote server over a cellular modem. However, I have not made the cellular modem the primary network adapter. I have made the modem's interface metric very high, so that by default sockets still open over WiFi. Because of this configuration, I have to specify the modem's IP if I want to connect using it.
However, when I run this code, the DNS lookup fails. For repro: my primary network adapter is a wireless network card, and I am connected to a local network that does not have internet access. I am connected over ethernet (second priority). I am connected to a USB cellular modem (lowest priority)
var net = require('net');
var sock = net.Socket();
const options = {
localAddress: "192.168.10.2", // address of a cellular modem
host: "google.com",
port: 5000
};
sock.connect(options);
sock.on('lookup', function(err, address, family, host) {
console.log(address);
// address variable has '10.0.0.1', not the actual address of the server
});
I was able to get to the bottom of this problem. The DNS lookup fails because dns.lookup() (used by default) does not use the network adapter that the socket tries to connect over. As I understand it, dns.lookup() uses a system tool that uses the primary network adapter. I don't think this is desirable behavior, but am not sure what to do about it. If a function exists in core that allows users to do DNS lookup over a specific network adapter, this should become the new default for sockets. If this function does not exist, I would like to see it added.
Activity
bnoordhuis commentedon Aug 4, 2017
Just so we're on the same page, the .localAddress option uses the address as-is, it doesn't do DNS resolution. I infer that isn't what you meant but I mention it in case I inferred wrong.
Not quite.
dns.lookup()uses a system tool, period.It sounds like the system resolver is configured incorrectly. That is not a node.js issue; you would have the same problem in another language or runtime.
bnoordhuis commentedon Aug 8, 2017
No follow-up so I'll assume this is working for you. Closing.
kodmanyagha commentedon Apr 17, 2020
how can I configure system resolver correctly?