Friday, January 5, 2018

Network Security: Promiscuous Mode

When a frame enters a NIC, if the destination Mac address is not the NIC's Mac address, a broadcast or a multicast, the NIC with drop the frame. Promiscuous mode is a mode for a wired or wireless NIC which causes the NIC to pass all traffic it receives up the networking stack on a machine. Now, the NIC will accept and read frames that have unicast addresses other than the NIC's Mac address. Of course, on a switch network, promiscuous mode is not useful since the switch will only send frames to ports associated with destination Mac addresses as listed in the switches CAM, content addressable memory table, also known as SAT, source address table. The one exception is an unknown unicast when a switch doesn't know which port a destination Mac address is associated with. The switch will flood the frame out of all ports except the port on which the frame originated. Normally, this won't be a problem because every data exchange should be preceded by an ARP request and an ARP reply. Which makes the communicating stations known to the switch before any data is transferred. In a future unit, we'll explore an attack and mitigation for actually seeing unknown unicasts contain data after the ARPs. On wi-fi networks with encryption using WPA Two, by default, packets to or from other hosts will not be able to be decrypted by the NIC. And will not be captured. So, promiscuous mode works the same as non-promiscuous mode. On wi-fi networks without encryption, promiscuous mode works, as it does on wired networks. Allowing NICs to read traffic with unicast addresses other than the NIC's Mac address. Monitor mode also allows a device with a wireless NIC to monitor all traffic received from a wireless network. The big difference between promiscuous mode and monitor mode is that monitor mode allows packets to be captured without having to associate with a wireless access point first. Another difference is that monitor mode only applies to wireless networks while promiscuous mode can be used on both wired and wireless networks. Monitor mode is like listening to people's conversations as you walk across the RIT campus.

Promiscuous mode is like sitting down with a bunch of people at a table, at a restaurant. You can hear conversations between other people at the same table. Each client on a WPA Two, PSK infrastructure has their own handshake. So, by default, you won't be able to monitor any traffic except your own on an encrypted network. However, if you know the preshared key and capture their handshake, you can decrypt their whole session.

1 comment:

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