MAC-Based Access Control is one method for preventing unauthorized access to the Wireless LAN. This article discusses how MAC-Based Access Control works and provides step-by-step configuration instructions for Microsoft NPS and Dashboard.
MAC-Based Access Control
We are starting to roll out ClearPass and MAC authentication using Cisco switches. We are having problems with Cisco phones and trying to profile them correctly. We have the following config on the ports Interface gig1/0/1 switchport access vlan 501 switchport mode access switchport voice vlan 6. Because the MAC address of the device is used as the authentication credentials, an attacker can easily gain network access by spoofing the MAC address of previously authenticated clients. Deploying MAC-Based Access Control in Cisco ISE Below are the steps necessary in order to deploy MAC-based Access Control in Cisco ISE.
A properly configured AP will attempt to authenticate a MAC address using Secure-PAP authentication with the ACS. The MAC addresses are entered into the ACS as users, with the username and password being the MAC address. From the ACS main menu, click on the USER SETUP button. (for local database mac) It seems my authentication only works if i program the mac address of the 'remote' wlc (the wlc holding the AP). This is a pitty, as i was hoping to centralise all 'appoved' mac addresses on the guest controller and not on each individual wlc seperatly. Also, suppose i want a radius server to validate the mac address. The RADIUS server used for authentication can vary depending on the network. The Tunnel-Password attribute is the field that is used on the RADIUS server to bind the MAC address and PSK. If the PSK matches the RADIUS server's entry for the client's MAC address, the wireless client is authenticated and associated on the wireless network.
It is critical to control which devices can access the wireless LAN. MAC-Based Access Control can be used to provide port based network access control on MR series access points. With MAC-Based Access Control, devices must be authenticated by a RADIUS server before network access is granted on an SSID. The AP (RADIUS client) sends a RADIUS Access-Request to the RADIUS server containing the username and password of the connecting wireless device. The username and password combination is always the MAC address of the connecting device, lower case without delimiting characters. If a RADIUS policy exists on the server that specifies the device should be granted access and the credentials are correct, the RADIUS server will respond with an Access-Accept message. Upon receiving this message, the AP will grant network access to the device on the SSID. If the RADIUS server replies with an Access-Reject because the device does not match a policy, the AP will not grant network access. Below is a diagram showing a successful authentication.
MAC-Based Access Control has some security implications which must be considered. One is that it is not an association method that supports wireless encryption. Therefore clients will need to rely on upper layer protocols for encrypting traffic such as SSL or IPsec once a device has gained network access. The second being the credentials used. Because the MAC address of the device is used as the credentials, an attacker can easily gain network access by spoofing the MAC address of previously authenticated clients. Below are the steps necessary in order, to deploy MAC-Based Access Control using Microsoft NPS.
Cisco promotes its Identity Services Engine (ISE) as “intuitive network security for the digital age.” But Switchzilla has just explained that it’s not very good at handling the growing practice of MAC address randomization by mobile devices.
A refresher: MAC addresses are unique identifiers assigned to network interface controllers, and are disclosed when devices communicate with each other on a network. MAC addresses were developed in more innocent times before we all started carrying networked devices around with us, and that they promiscuously probe Wi-Fi hotspots and Bluetooth gizmos prior to initiating connections. Those probes, and human-initiated connections, are often made without regard for the fact that it’s possible to track a device through space by following its MAC address from network to network.
The tech world wised up to this, and started to program devices to periodically randomize their MAC addresses when probing so that the handhelds stopped leaving such easy-to-follow breadcrumb trails. This probing technique appeared in version 8 of both iOS and Android, in 2014 and 2017 respectively. Android 10 added MAC address randomization for all network activities in 2019; iOS 14 added it this week. Windows 10 has had it for a while, too.
Which brings us to September 15, 2020, when Cisco disclosed in a field notice that “Identity Services Engine MAC Address Lookup Might Fail with Android 10 and Apple iOS 14 Devices Due to the Use of MAC Randomization on the Mobile Client Devices.”
The field notice explains that unless ISE is fed policies to handle MAC address randomization, “previously provisioned mobile devices and the policies configured based on profiling identity groups might be incorrectly matched after the new MAC address randomization behavior takes effect.
“This could result in network connectivity disruption for these mobile devices.”
Cisco explains the cause of the problem as follows:
Even though the Android 10 and iOS 14 devices are set up to use randomized MAC addresses, when a wireless profile is created on the device the MAC address is always generated with the same random MAC address for the given wireless profile. This is true even when the wireless profile is deleted and recreated. However, when the dual-SSID BYOD flow is used, different MAC addresses will be generated for the onboarding SSID and the secured SSID. This causes a policy mismatch when using the precreated ISE BYOD Employee_EAP-TLS authorization rule.
![For For](https://supportforums.cisco.com/legacyfs/online/legacy/5/6/8/96865-ISE_Author_Pf.png)
This also impacts the single-SSID BYOD flow for devices that have been onboarded while running a previous version of iOS. Prior to iOS 14, the device uses a real MAC address for wireless access. However, upon upgrade to iOS 14, all existing wireless profiles will be updated to use random MAC addresses. Since the MAC address used during the previous version of iOS and after iOS 14 is different, authentication might fail if MAC address related conditions are used in conjunction with BYOD.
iOS 14, which became available today, therefore seems to be a part of the problem. But not all of it because ISE has offered MAC randomization workarounds in March 2020 prior to version 14's official release.
Cisco Authentication List
Cisco’s latest field notice advises: “There is currently no large scale solution for the issues introduced by third-party MAC address randomization, only workarounds are available.” That workaround is detailed in the field notice, and has five steps; it doesn’t look horribly onerous.
The Register leaves it to our readers to decide if the need for a workaround represents “intuitive network security for the digital age.” ®
Cisco Authentication Port Control Auto
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