The RADIUS security system is a distributed server or client for a secure network against unauthorized access. The are several steps to configure RADIUS authentication on the cisco router, so let get started.

Step 1: Use a computer laptop connect to the Cisco Router
Step 2: Configure hostname CCNA-R1
Step 3: Configure CCNA-R1 using the IP address of each interface (Fa0/0: netmask: Fa0/1: netmask: and no shutdown to enable both interfaces to active.
Router#config t
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#hostname CCNA-R1
CCNA-R1(config)#interface fastEthernet 0/0
CCNA-R1(config-if)#ip add
CCNA-R1(config-if)#ip address
CCNA-R1(config-if)#no sh
CCNA-R1(config-if)#no shutdown

%LINK-5-CHANGED: Interface FastEthernet0/0, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up

CCNA-R1(config-if)#int fa0/1
CCNA-R1(config-if)#ip add
CCNA-R1(config-if)#no sh
CCNA-R1(config-if)#no shutdown

%LINK-5-CHANGED: Interface FastEthernet0/1, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to up


Step 4: Configure Radius authentication for Telnet access on CCNA-R1

RADIUS Server host:
RADIUS Secret Key: P@ssw0rd

a. Configuration on CCNA-R1

We are using the command line, aaa new-model, to tell the router that you’re using either RADIUS for authentication.

CCNA-R1(config)#aaa new-model

b. Tells the router the IP address of the RADIUS server and the shared secret.

CCNA-R1(config)#radius-server key p@ssword
CCNA-R1(config)#radius-server host key P@ssw0rd

c. The aaa authentication command is used to start RADIUS authentication on the router as a default method for login.

CCNA-R1(config)#aaa new-model
CCNA-R1(config)#aaa authentication login default group radius local

g. Configuration of the virtual teletype interfaces for login

CCNA-R1(config)#line vty 0 4
CCNA-R1(config-line)#login authentication default
CCNA-R1(config-line)#do copy run start
Destination filename [startup-config]?
Building configuration…

Step 5: Test connectivity to CCNA-R1 by ping from the laptop

Packet Tracer PC Command Line 1.0

Pinging with 32 bytes of data:

Request timed out.
Reply from bytes=32 time=3ms TTL=127
Reply from bytes=32 time<1ms TTL=127
Reply from bytes=32 time=10ms TTL=127

Ping statistics for
Packets: Sent = 4, Received = 3, Lost = 1 (25% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 10ms, Average = 4ms


Step 6: Test telnet connectivity to CCNA-R1 and authentication
Username: ccna
Password: cisco
Trying …Open

User Access Verification

Username: ccna


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RADIUS Authentication on Cisco Router on YouTube

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