RADIUS AAA

Cumulus Linux provides add-on packages to enable RADIUS users to log into the switch transparently with minimal configuration. There is no need to create accounts or directories on the switch. Authentication uses PAM and includes login, ssh, sudo and su.

Install the RADIUS Packages

If you use Linux commands to configure RADIUS AAA, you must install the RADIUS libnss-mapuser and libpam-radius-auth packages before you start configuration. The packages are in the cumulus-local-apt-archive repository, which is embedded in the Cumulus Linux image. You can install the packages even when the switch is not connected to the internet.

To install the RADIUS packages:

cumulus@switch:~$ sudo apt-get update
cumulus@switch:~$ sudo apt-get install libnss-mapuser libpam-radius-auth

cumulus@switch:~$ sudo apt-get -y -o Dpkg::Options::=--force-confnew install libnss-mapuser libpam-radius-auth

After installation completes, either reboot the switch or run the sudo systemctl restart nvued command.

The nvshow group includes the radius_user account, and the nvset and nvapply groups. The sudo groups include the radius_priv_user account. This enables all RADIUS logins to run NVUE nv show commands and all privileged RADIUS users to also run nv set, nv unset, and nv apply commands, and to use sudo.

Required RADIUS Client Configuration

After you install the required RADIUS packages, configure the following required settings on the switch (the RADIUS client):

• Set the IP address or hostname of at least one RADIUS server. You can specify a port for the server (optional). The default port number is 1812.
• Set the secret key shared between the RADIUS server and client. If you include special characters in the key (such as $), you must enclose the key in single quotes (').
• If you use NVUE commands to configure RADIUS, you must also:
  • Set the priority at which Cumulus Linux contacts a RADIUS server for load balancing. You can set a value between 1 and 100. The lower value is the higher priority.
  • Set the priority for the authentication order for local and RADIUS users. You can set a value between 1 and 100. The lower value is the higher priority.
  • Enable RADIUS.

cumulus@switch:~$ nv set system aaa radius server 192.168.0.254 port 42
cumulus@switch:~$ nv set system aaa radius server 192.168.0.254 secret 'myradius$key'
cumulus@switch:~$ nv set system aaa radius server 192.168.0.254 priority 10
cumulus@switch:~$ nv set system aaa authentication-order 10 radius
cumulus@switch:~$ nv set system aaa authentication-order 20 local
cumulus@switch:~$ nv set system aaa radius enable on
cumulus@switch:~$ nv config apply

...
mapped_priv_user   radius_priv_user

# server[:port]    shared_secret   timeout (secs)  src_ip
192.168.0.254:42   myradius$key       3
...

Optional RADIUS Configuration

You can configure the following global RADIUS settings and server specific settings.

cumulus@switch:~$ nv set system aaa radius vrf mgmt
cumulus@switch:~$ nv set system aaa radius privilege-level 10
cumulus@switch:~$ nv set system aaa radius retransmit 8
cumulus@switch:~$ nv set system aaa radius timeout 10
cumulus@switch:~$ nv set system aaa radius source-ipv4 192.168.1.10
cumulus@switch:~$ nv set system aaa radius debug enable
cumulus@switch:~$ nv config apply

cumulus@switch:~$ nv set system aaa radius server 192.168.0.254 source-ip 192.168.1.10
cumulus@switch:~$ nv set system aaa radius server 192.168.0.254 timeout 10
cumulus@switch:~$ nv config apply

...
# Set the minimum privilege level in VSA attribute shell:privilege-level=VALUE
# default is 15, range is 0-15.
privilege-level 10
#
#  Uncomment to enable debugging, can be used instead of altering pam files
debug
#
# Account for privileged radius user mapping.  If you change it here,  you need
# to change /etc/nss_mapuser.conf as well
mapped_priv_user radius_priv_user

# server[:port]                                    shared_secret       timeout (secs)     src_ip
192.168.0.254:42                                   myradius$key        10                 192.168.1.10        

vrf-name mgmt

Enable Login without Local Accounts

LDAP is not commonly used with switches and adding accounts locally is cumbersome, Cumulus Linux includes a mapping capability with the libnss-mapuser package.

Mapping uses two NSS (Name Service Switch) plugins, one for account name, and one for UID lookup. The installation process configures these accounts automatically in the /etc/nsswitch.conf file and removes them when you delete the package. See the nss_mapuser (8) man page for the full description of this plugin.

A username is mapped at login to a fixed account specified in the configuration file, with the fields of the fixed account used as a template for the user that is logging in.

For example, if you look up the name dave and the fixed account in the configuration file is radius\_user, and that entry in /etc/passwd is:

radius_user:x:1017:1002:radius user:/home/radius_user:/bin/bash

then the matching line that returns when you run getent passwd dave is:

cumulus@switch:~$ getent passwd dave
dave:x:1017:1002:dave mapped user:/home/dave:/bin/bash

The login process creates the home directory /home/dave if it does not already exist and populates it with the standard skeleton files by the mkhomedir_helper command.

The configuration file /etc/nss_mapuser.conf configures the plugins. The file includes the mapped account name, which is radius_user by default. You can change the mapped account name by editing the file. The nss_mapuser (5) man page describes the configuration file.

A flat file mapping derives from the session number assigned during login, which persists across su and sudo. Cumulus Linux removes the mapping at logout.

Local Fallback Authentication

If a site wants to allow local fallback authentication for a user when none of the RADIUS servers are reachable, you can add a privileged user account as a local account on the switch. The local account must have the same unique identifier as the privileged user and the shell must be the same.

To configure local fallback authentication:

1. Add a local privileged user account. For example, if the radius_priv_user account in the /etc/passwd file is radius_priv_user:x:1002:1001::/home/radius_priv_user:/sbin/radius_shell, run the following command to add a local privileged user account named johnadmin:

   cumulus@switch:~$ sudo useradd -u 1002 -g 1001 -o -s /sbin/radius_shell johnadmin
   

2. To enable the local privileged user to run sudo and NVUE commands, run the following commands:

   cumulus@switch:~$ sudo adduser johnadmin nvset
   cumulus@switch:~$ sudo adduser johnadmin nvapply
   cumulus@switch:~$ sudo adduser johnadmin sudo
   cumulus@switch:~$ sudo systemctl restart nvued
   

3. Edit the /etc/passwd file to move the local user line before to the radius_priv_user line:

   cumulus@switch:~$ sudo vi /etc/passwd
   ...
   johnadmin:x:1002:1001::/home/johnadmin:/sbin/radius_shell
   radius_priv_user:x:1002:1001::/home/radius_priv_user:/sbin/radius_shell
   

4. To set the local password for the local user, run the following command:

   cumulus@switch:~$ sudo passwd johnadmin
   

Verify RADIUS Client Configuration

To verify the RADIUS client configuration, log in as a non-privileged user and run the nv set interface command.

In this example, the ops user is not a privileged RADIUS user so the ops user cannot add an interface.

ops@leaf01:~$ nv set interface swp1
ERROR: User ops does not have permission to make networking changes.

In this example, the admin user is a privileged RADIUS user (with privilege level 15) so is able to add interface swp1.

admin@leaf01:~$ nv set interface swp1
admin@leaf01:~$ nv apply

Show RADIUS Configuration

To show global RADIUS configuration, run the nv show system aaa radius command:

cumulus@switch:~$ nv show system aaa radius
                 operational    applied      
---------------  -------------  -------------
enable           on             on           
vrf              mgmt           mgmt         
debug            disabled       disabled     
privilege-level                 15           
retransmit       0              0            
port                            1812         
timeout                         3            
[server]         192.168.0.254  192.168.0.254

To show all RADIUS configured servers, run the nv show system aaa radius server command:

cumulus@switch:~$ nv show system aaa radius server
Hostname       Port  Priority  Password  source-ip     Timeout
-------------  ----  --------  --------  ------------  -------
192.168.0.254  42    1         *         192.168.1.10  10

To show configuration for a specific RADIUS server, run the nv show system aaa radius server <server> command:

cumulus@switch:~$ nv show system aaa radius server 192.168.0.254
           operational   applied     
---------  ------------  ------------
port       42            42          
timeout    10            10          
secret     *             *           
priority   1             10          

Remove RADIUS Client Packages

Remove the RADIUS packages with the following command:

cumulus@switch:~$ sudo apt-get remove libnss-mapuser libpam-radius-auth

When you remove the packages, Cumulus Linux deletes the plugins from the /etc/nsswitch.conf file and from the PAM files.

To remove all configuration files for these packages, run:

cumulus@switch:~$ sudo apt-get purge libnss-mapuser libpam-radius-auth

To remove the home directories of the RADIUS users, obtain the list by running the following command:

cumulus@switch:~$ sudo ls -l /home | grep radius

For all users listed, except the radius_user, run the following command to remove the home directories:

cumulus@switch:~$ sudo deluser --remove-home USERNAME

USERNAME is the account name (the home directory relative portion). This command gives the following warning because the user is not listed in the /etc/passwd file.

userdel: cannot remove entry 'USERNAME' from /etc/passwd
/usr/sbin/deluser: `/usr/sbin/userdel USERNAME' returned error code 1. Exiting.

After you remove all the RADIUS users, run the command to remove the fixed account. If there are changes to the account in the /etc/nss_mapuser.conf file, use that account name instead of radius_user.

cumulus@switch:~$ sudo deluser --remove-home radius_user
cumulus@switch:~$ sudo deluser --remove-home radius_priv_user
cumulus@switch:~$ sudo delgroup radius_users

Considerations

• If two or more RADIUS users log in simultaneously, a UID lookup only returns the user that logs in first. Any process that either user runs applies to both, and all files that either user creates apply to the first name matched. This process is similar to adding two local users to the password file with the same UID and GID, and is an inherent limitation of using the UID for the fixed user from the password file. The current algorithm returns the first name matching the UID from the mapping file, which is either the first or second user that logs in.

• When you install both the TACACS+ and the RADIUS AAA client, Cumulus Linux does not attempt the RADIUS login. As a workaround, do not install both the TACACS+ and the RADIUS AAA client on the same switch.

• When the RADIUS server is reachable outside of the management VRF, such as the default VRF, you might see the following error message when you try to run sudo:

  2008-10-31T07:06:36.191359+00:00 SW01 sudo: pam_radius_auth(sudo:auth): Bind for server 10.1.1.25 failed: Cannot assign requested address
  2008-10-31T07:06:36.192307+00:00 sw01 sudo: pam_radius_auth(sudo:auth): No valid server found in configuration file /etc/pam_radius_auth.conf
  

  The error occurs because sudo tries to authenticate to the RADIUS server through the management VRF. Before you run sudo, you must set the shell to the correct VRF:

  cumulus@switch:~$ vrf exec default bash
  cumulus@switch:~$ sudo