Summary: This note outlines best practices for deploying TACACS+ on Cisco IOS-XE devices, focusing on security, redundancy, and efficient management.
- Redundancy: Always deploy at least two TACACS+ servers for high availability. Configure your IOS-XE devices to use multiple server hosts to ensure continuous authentication and authorization services even if one server fails.
- Shared Key: Use strong, complex, and consistent shared keys across all TACACS+ servers and IOS-XE devices. This key is crucial for securing communication between the client (IOS-XE) and the server.
- Load Balancing: If using multiple servers, consider implementing a load-balancing mechanism (e.g., round-robin or least-connections) at the server level, or configure multiple server groups on the IOS-XE device for distribution.
- Time Synchronization: Ensure accurate NTP synchronization between IOS-XE devices and TACACS+ servers to prevent authentication issues related to time skews.
- Enable AAA New-Model: Always start by enabling the AAA new-model for modern AAA services:
aaa new-model
- Define TACACS+ Server Groups: Group your TACACS+ servers for redundancy and easier management. Specify the server IP addresses and the shared key.
aaa group server tacacs+ TACACS_SERVERS
server name TACACS_SERVER_1
server name TACACS_SERVER_2
!
tacacs server TACACS_SERVER_1
address ipv4 10.10.10.1
key <STRONG_SHARED_KEY>
tacacs server TACACS_SERVER_2
address ipv4 10.10.10.2
key <STRONG_SHARED_KEY>
- Authentication:
- Login Authentication: Configure line console, VTY, and auxiliary lines to use TACACS+ for login authentication, with a local fallback option for emergencies.
aaa authentication login default group TACACS_SERVERS local
line vty 0 15
login authentication default
line console 0
login authentication default
- Enable Authentication: For privileged EXEC mode, use TACACS+ if required.
aaa authentication enable default group TACACS_SERVERS enable
- Authorization:
- Accounting: Configure accounting to log user activity, including login/logout and executed commands, to the TACACS+ server. This is vital for auditing and security.
aaa accounting exec default start-stop group TACACS_SERVERS
aaa accounting commands 1 default start-stop group TACACS_SERVERS
aaa accounting commands 15 default start-stop group TACACS_SERVERS
- Source Interface: Explicitly define a source interface for TACACS+ traffic to ensure consistent communication and simplify firewall rules.
ip tacacs source-interface GigabitEthernet0/0
¶ 3. Network Connectivity and Security
- Reachability: Ensure full IP reachability between IOS-XE devices and TACACS+ servers. Verify using
ping and traceroute.
- Firewall Rules: Configure firewalls to allow TCP port 49 (TACACS+) traffic between IOS-XE devices and the TACACS+ servers.
- Transport Layer Security: While TACACS+ encrypts the entire packet body, consider securing the transport further if traversing untrusted networks (e.g., IPsec VPNs) for maximum protection.
- Local Fallback: Always configure a local fallback mechanism (e.g.,
local keyword in AAA methods) for authentication and authorization. This ensures network administrators can still access devices if TACACS+ servers are unreachable.
- Hardening Local Accounts: If local fallback is used, ensure local accounts are strong, well-managed, and used only for emergency access.
¶ 4. Testing and Monitoring
- Thorough Testing: After initial configuration, rigorously test all authentication, authorization, and accounting functionalities from various access points (console, SSH, Telnet) and with different user roles.
- Logging and Monitoring: Configure IOS-XE devices to send syslog messages to a central logging server. Monitor TACACS+ server logs for authentication failures or unauthorized access attempts.
- Regular Audits: Periodically review TACACS+ configurations on both the servers and the IOS-XE devices, as well as access policies, to ensure they align with security policies.
- Troubleshooting Commands: Utilize commands like
show tacacs, debug tacacs authentication, debug aaa authentication, debug aaa authorization to troubleshoot issues.
By following these best practices, you can establish a robust, secure, and highly available TACACS+ deployment for managing your Cisco IOS-XE network devices.