Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 114

MAC Authentication Bypass MAC authentication bypass (MAB) enables you to provide MAC-based security by allowing only known MAC addresses within the network using a RADIUS server. 802.1X-enabled clients can authenticate themselves using the 802.1X protocol. Other devices that do not use 802.1X - like IP phones, printers, and IP fax machines - still need connectivity to the network. The guest VLAN provides one way to access the network. However, placing trusted devices on the quarantined VLAN is not the best practice. MAB allows devices that have known static MAC addresses to be authenticated using their MAC address, and places them into a VLAN different from the VLAN in which unknown devices are placed. For an 802.1X-incapable device, 802.1X times out if the device does not respond to the Request Identity frame. If MAB is enabled, the port is then put into learning state and waits indefinitely until the device sends a packet. Once its MAC is learned, it is sent for authentication to the RADIUS server (as both the username and password, in hexadecimal format without any colons). If the server authenticates successfully, the port is dynamically assigned to a MAB VLAN using a RADIUS attribute 81, or is assigned to the untagged VLAN of the port. Afterward, packets from any other MAC address are dropped. If authentication fails, the authenticator waits the quiet-period and then restarts the authentication process. MAC authentication bypass works in conjunction and in competition with the guest VLAN and authentication-fail VLAN. When both features are enabled: 1. If authentication fails, the port it is placed into the authentication-fail VLAN. 2. If the host does not respond to the Request Identity frame, the port transitions to MAB initiation state. 3. If MAB times out or MAC authentication fails, the port is placed into the guest VLAN. If both MAB and re-authentication are enabled, when the re-auth period finishes and whether the previous authentication was through MAB or 802.1X, 802.1X authentication is tried first. If 802.1X times out, MAB authentication is tried. The port remains authorized throughout the reauthentication process. Once a port is enabled/disabled through 802.1X authentication, changes to MAB do not take effect until the MAC is asked to re-authenticate or the port status is toggled. MAB in Single-host and Multi-Host Mode In single-host and multi-host mode, the switch attempts to authenticate a supplicant using 802.1X. If 802.1X times out because the supplicant does not respond to the Request Identity frame and MAB is enabled, the switch attempts to authenticate the first MAC it learns on the port. Afterwards, for singlehost mode, traffic from all other MACs is dropped; for multi-host mode, all traffic from all other MACs is accepted. After a port is authenticated by MAB, if the switch detects an 802.1X EAPoL start message from the authenticated MAC, the switch re-authenticates using 802.1X first, while keeping the port authorized. NOTE: If the switch is in multi-host mode, a MAC address that was MAB-authenticated but later was disabled from MAB authentication, is not denied access but moved to the guest VLAN. If the switch is in single-host mode, the MAC address is disallowed access. MAB in Multi-Supplicant Authentication Mode Multi-supplicant authentication (multi-auth) mode is similar to other 802.1X modes in that the switch first attempts to authenticate a supplicant using 802.1X. 802.1X times out if the supplicant does not respond 114 802.1X