Chewie uses PAE Group address as SA

[knollpoi]

I am using Chewie as a standalone authenticator (as a component in a system outside of faucetsdn) for a switch that does not have a built-in authenticator.

When a supplicant attached to the switch sends an EAPOL-Start, it sets the DA to the PAE Group address (01-80-C2-00-00-03), and SA to its own MAC address.

Chewie receives the EAPOL-Start and responds, as expected, with an EAPOL-EAP message. This message sets DA to the MAC address of the supplicant, and SA to the PAE Group Address.

I believe setting SA=PAE Group Address is invalid, and is being dropped by the supplicant and/or other network elements in the path between Chewie and the supplicant (depending on the specific network topology I am testing).

I think the cause of this is that Chewie is simply setting the SA of sent EAPOL frames to the port_id which is copied from the DA of the received EAPOL-Start. I think the fix is as simple as checking if the received DA is 01-80-C2-00-00-03, and if it is, setting port_id to the local MAC address.

I am willing to submit a patch to fix this, but it is unclear where in the code is best to make this check.

Please provide guidance and I will make my best attempt to supply a patch.

[gizmoguy]

Hi @knoll01,

Thanks for reporting this issue and interested in hearing how integrating Chewie with other switches go, we haven't done much integration testing with external systems that aren't faucet as yet.

I took a look at this and I think the piece we need to modify is this function:

chewie/chewie/chewie.py

Lines 300 to 307 in dab415d

	eap_queue_message = self.eap_output_messages.get()
	self.logger.info("Sending message %s from %s to %s",
	eap_queue_message.message,
	str(eap_queue_message.port_mac),
	str(eap_queue_message.src_mac))
	self.eap_socket.send(MessagePacker.ethernet_pack(eap_queue_message.message,
	eap_queue_message.port_mac,
	eap_queue_message.src_mac))

If you want to attempt to get a patch out, then I'm happy to review it, or if that code doesn't make sense I'm happy to take a crack at fixing it.