Administrator Guide

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.
This module requires NAS for handling the access challenge from the RADIUS server. NAS sends the input OTP in an Access-
Request to the RADIUS server, and the user authentication succeeds or fails depending upon the Access-Accept or Access-
Reject response received at NAS from the RADIUS server.
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Security