Administrator Guide

• If the credentials are valid:
• RADIUS server sends a request to the SMS–OTP daemon to generate an OTP for the user.
• A challenge authentication is sent from the RADIUS server as Reply–Message attribute.
• If the Reply–Message attribute is not sent from the RADIUS server, the default text is the Response.
• 2FA is successful only on providing the correct OTP.
• If the credentials are invalid, the authentication fails.
NOTE: 2FA does not support RADIUS authentications done with REST, Web UI, and OMI.
Handling Access-Challenge Message
To provide a two-step verification in addition to the username and password, NAS prompts for additional information. An Access-
Challenge request is sent from the RADIUS server to NAS.
The RADIUS server returns one of the following responses:
• Access-Challenge—If the user credentials are valid, the NAS server receives an Access-Challenge request from the RADIUS server.
• Access-Accept—NAS validates the username and password. If the credentials are valid, the RADIUS server sends an Access-
Request to the short message service one time password (SMS-OTP) daemon to generate an OTP. The OTP is sent to the user’s e-
mail ID or mobile. If the OTP is valid, the RADIUS server authenticates the 2FA user and sends an Access-Accept response to NAS.
• Access-Reject—NAS validates the OTP and if the OTP is invalid, the RADIUS server does not authenticate the user and sends an
Access-Reject response to NAS.
Configuring Challenge Response Authentication for SSHv2
To configure challenge response authentication for SSHv2, perform the following steps:
1. Enable challenge response authentication for SSHv2.
CONFIGURATION mode
ip ssh challenge-response-authentication enable
2. View the configuration.
EXEC mode
show ip ssh
DellEMC# show ip ssh
SSH server : enabled.
SSH server version : v2.
SSH server vrf : default.
SSH server ciphers : aes256-ctr,aes256-cbc,aes192-ctr,aes192-cbc,aes128-ctr,aes128-
cbc,3des-cbc.
SSH server macs : hmac-sha2-256,hmac-sha1,hmac-sha1-96,hmac-md5,hmac-md5-96.
SSH server kex algorithms : diffie-hellman-group-exchange-sha1,diffie-hellman-group1-
sha1,diffie-hellman-group14-sha1.
Password Authentication : enabled.
Hostbased Authentication : disabled.
RSA Authentication : disabled.
Challenge Response Auth : enabled.
Vty Encryption HMAC Remote IP
2 aes128-cbc hmac-md5 10.16.127.141
4 aes128-cbc hmac-md5 10.16.127.141
* 5 aes128-cbc hmac-md5 10.16.127.141
DellEMC#
SMS-OTP Mechanism
A short message service one time password (SMS-OTP) is a free RADIUS module to implement two factor authentication. There are
multiple 2FA mechanisms that can be deployed with the RADIUS. Mechanisms such as the Google authenticator do not rely on the
Access-Challenge message and the SMS-OTP module rely on the Access-challenge message. The main objective of this feature is to
handle the Access-Challenge messages and sends the Access-Request message with user’s response.
Security
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