Comnet CNGE11FX3TX8MS, Инструкция по установке и эксплуатации

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INS_CNGE11FX3TX8MS[POE][HO] Rev. 11.6.17 PAGE 62
INSTRUCTION MANUAL CNGE11FX3TX8MS[POE][HO]
TECH SUPPORT: 1.888.678.9427
Object Description
Admin State
If NAS is globally enabled, this selection controls the port’s authentication mode. The following modes are available:
Force Authorized
In this mode, the switch will send one EAPOL Success frame when the port link comes up, and any client on the port will be
allowed network access without authentication.
Force Unauthorized
In this mode, the switch will send one EAPOL Failure frame when the port link comes up, and any client on the port will be
disallowed network access.
Port-based 802.1X
In the 802.1X-world, the user is called the supplicant, the switch is the authenticator, and the RADIUS server is the authentication
server. The authenticator acts as the man-in-the-middle, forwarding requests and responses between the supplicant and the
authentication server. Frames sent between the supplicant and the switch are special 802.1X frames, known as EAPOL (EAP
Over LANs) frames. EAPOL frames encapsulate EAP PDUs (RFC3748). Frames sent between the switch and the RADIUS server
are RADIUS packets. RADIUS packets also encapsulate EAP PDUs together with other attributes like the switch’s IP address,
name, and the supplicant’s port number on the switch. EAP is very flexible, in that it allows for different authentication methods,
like MD5-Challenge, PEAP, and TLS. The important thing is that the authenticator (the switch) doesn’t need to know which
authentication method the supplicant and the authentication server are using, or how many information exchange frames are
needed for a particular method. The switch simply encapsulates the EAP part of the frame into the relevant type (EAPOL or
RADIUS) and forwards it.
When authentication is complete, the RADIUS server sends a special packet containing a success or failure indication. Besides
forwarding this decision to the supplicant, the switch uses it to open up or block traffic on the switch port connected to the
supplicant.
Note: Suppose two backend servers are enabled and that the server timeout is configured to X seconds (using the AAA
configuration page), and suppose that the first server in the list is currently down (but not considered dead). Now, if the supplicant
retransmits EAPOL Start frames at a rate faster than X seconds, then it will never get authenticated, because the switch will cancel
on-going backend authentication server requests whenever it receives a new EAPOL Start frame from the supplicant. And since
the server hasn’t yet failed (because the X seconds haven’t expired), the same server will be contacted upon the next backend
authentication server request from the switch. This scenario will loop forever. Therefore, the server timeout should be smaller than
the supplicant’s EAPOL Start frame retransmission rate.
Single 802.1X
In port-based 802.1X authentication, once a supplicant is successfully authenticated on a port, the whole port is opened for
network traffic. This allows other clients connected to the port (for instance through a hub) to piggy-back on the successfully
authenticated client and get network access even though they really aren’t authenticated. To overcome this security breach, use
the Single 802.1X variant.
Single 802.1X is really not an IEEE standard, but features many of the same characteristics as does port-based 802.1X. In Single
802.1X, at most one supplicant can get authenticated on the port at a time. Normal EAPOL frames are used in the communication
between the supplicant and the switch. If more than one supplicant is connected to a port, the one that comes first when the
port’s link comes up will be the first one considered. If that supplicant doesn’t provide valid credentials within a certain amount
of time, another supplicant will get a chance. Once a supplicant is successfully authenticated, only that supplicant will be allowed
access. This is the most secure of all the supported modes. In this mode, the Port Security module is used to secure a supplicant’s
MAC address once successfully authenticated.
Multi 802.1X
Multi 802.1X is - like Single 802.1X - not an IEEE standard, but a variant that features many of the same characteristics. In Multi
802.1X, one or more supplicants can get authenticated on the same port at the same time. Each supplicant is authenticated
individually and secured in the MAC table using the Port Security module.
In Multi 802.1X it is not possible to use the multicast BPDU MAC address as destination MAC address for EAPOL frames sent from
the switch towards the supplicant, since that would cause all supplicants attached to the port to reply to requests sent from the
switch. Instead, the switch uses the supplicant’s MAC address, which is obtained from the first EAPOL Start or EAPOL Response
Identity frame sent by the supplicant. An exception to this is when no supplicants are attached. In this case, the switch sends
EAPOL Request Identity frames using the BPDU multicast MAC address as destination - to wake up any supplicants that might be
on the port.
The maximum number of supplicants that can be attached to a port can be limited using the Port Security Limit Control
functionality.
MAC-based Auth.
Unlike port-based 802.1X, MAC-based authentication is not a standard, but merely a best-practices method adopted by the
industry. In MAC-based authentication, users are called clients, and the switch acts as the supplicant on behalf of clients. The
initial frame (any kind of frame) sent by a client is snooped by the switch, which in turn uses the client’s MAC address as both
username and password in the subsequent EAP exchange with the RADIUS server. The 6-byte MAC address is converted to a
string on the following form “xx-xx-xx-xx-xx-xx”, that is, a dash (-) is used as separator between the lower-cased hexadecimal digits.
The switch only supports the MD5-Challenge authentication method, so the RADIUS server must be configured accordingly.
When authentication is complete, the RADIUS server sends a success or failure indication, which in turn causes the switch to open
up or block traffic for that particular client, using the Port Security module. Only then will frames from the client be forwarded on
the switch. There are no EAPOL frames involved in this authentication, and therefore, MAC-based Authentication has nothing to
do with the 802.1X standard.
The advantage of MAC-based authentication over 802.1X-based authentication is that the clients don’t need special supplicant
software to authenticate. The disadvantage is that MAC addresses can be spoofed by malicious users - equipment whose MAC
address is a valid RADIUS user can be used by anyone. Also, only the MD5-Challenge method is supported. The maximum
number of clients that can be attached to a port can be limited using the Port Security Limit Control functionality.