C
HAPTER
4
| Configuring the Switch
Configuring Security
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standard defines a port-based access control procedure that prevents
unauthorized access to a network by requiring users to first submit
credentials for authentication. Access to all switch ports in a network can
be centrally controlled from a server, which means that authorized users
can use the same credentials for authentication from any point within the
network.
Figure 27: Using Port Security
This switch uses the Extensible Authentication Protocol over LANs (EAPOL)
to exchange authentication protocol messages with the client, and a
remote RADIUS authentication server to verify user identity and access
rights. These backend servers are configured on the AAA menu (see
page 109).
When a client (i.e., Supplicant) connects to a switch port, the switch (i.e.,
Authenticator) responds with an EAPOL identity request. The client
provides its identity (such as a user name) in an EAPOL response to the
switch, which it forwards to the RADIUS server. The RADIUS server verifies
the client identity and sends an access challenge back to the client. The
EAP packet from the RADIUS server contains not only the challenge, but
the authentication method to be used. The client can reject the
authentication method and request another, depending on the
configuration of the client software and the RADIUS server. The encryption
method used by IEEE 802.1X to pass authentication messages can be MD5
(Message-Digest 5), TLS (Transport Layer Security), PEAP (Protected
Extensible Authentication Protocol), or TTLS (Tunneled Transport Layer
Security). However, note that the only encryption method supported by
MAC-Based authentication is MD5. The client responds to the appropriate
method with its credentials, such as a password or certificate. The RADIUS
server verifies the client credentials and responds with an accept or reject
packet. If authentication is successful, the switch allows the client to
access the network. Otherwise, network access is denied and the port
remains blocked.
802.1x
client
RADIUS
server
1. Client attempts to access a switch port.
2. Switch sends client an identity request.
3. Client sends back identity information.
4. Switch forwards this to authentication server.
5. Authentication server challenges client.
6. Client responds with proper credentials.
7. Authentication server approves access.
8. Switch grants client access to this port.
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