NWEthernetChannel not working as expected - swift

Question

The "Advances in Networking" talk for WWDC2019 featured a new class, introduced in Mac OS X 10.15 called NWEthernetChannel to monitor a custom (non-IP) protocol. This is for MacOS.
I am interested in monitoring Cisco Discovery Protocol (CDP) packets, however, the class is not working as expected - the receiveHandler is not receiving any data.
What I verified:
NWEthernetChannel is alive and in the ready state, monitoring the active NWInterface called eth0.
As per the documentation, the com.apple.developer.networking.custom-protocol entitlement is set.
I verified the same logic using sudo tcpdump -nn -v -i en0 -s 1500 'ether[20:2] == 0x2000'. This returned the expected result.
Please see my implementation below:
self._ethernetChannel = NWEthernetChannel(on: self._ethernetInterface!, etherType: 0x2000)
self._ethernetChannel!.stateUpdateHandler = {state in switch state {
case .ready:
NSLog("ready");
break;
case .waiting(let error as NWError):
print("Waiting:", error);
break;
case .failed(let error as NWError):
print("Failed:", error);
break;
case .cancelled:
print("cancelled");
break;
case .preparing:
print("preparing");
break;
case .setup:
print("setup");
default:
NSLog("default");
break;
}}
self._ethernetChannel!.receiveHandler = {(packetData, vlanTag, localAddress, remoteAddress) in
print("received data");
};
self._ethernetChannel!.start(queue: .main);
Can someone shed some light?