Cisco NX-OS/IOS Configuration Basics Comparison

Cisco NXOS and IOS are two different operating systems used on different Cisco devices. NXOS is used on Cisco’s Nexus line of data center switches, while IOS (Internetwork Operating System) is used on most Cisco routers and switches outside of the Nexus line.

Here are some basic comparisons between the configuration of the two:

1. Configuration Modes:

• IOS: To configure most settings, you must enter Global Configuration mode with the `configure terminal` command.
• NXOS: There is no specific Global Configuration mode. Most commands that would be placed in Global Configuration mode in IOS can be placed in the normal enabled (privileged EXEC) mode in NXOS.

2. Saving Configurations:

• IOS: Configuration changes must be saved manually using `copy runningconfig startupconfig` (or `write memory`) to persist through reboots.
• NXOS: Changes to the configuration are saved automatically and persist through reboots.

3. Interfaces Configuration:

• IOS: You have to navigate to each interface to configure it (using `interface` command).
• NXOS: Supports configuring multiple interfaces at once using the `interface range` command.

4. Feature Control:

• IOS: Most features are enabled by default.
• NXOS: Many features are disabled by default and must be enabled manually using the `feature` command (like `feature interfacevlan` to enable VLAN interfaces).

5. VLAN Configuration:

• IOS: VLANs are configured in the global config mode.
• NXOS: VLANs are configured in their own config mode.

6. File System:

• IOS: Uses a hierarchical file system (like Unix).
• NXOS: Uses a checkpoint/rollback file system that allows the administrator to take a snapshot (checkpoint) of the configuration and roll back to that point if necessary.

7. VRFs:

• IOS: Default VRF is known as “global” and management VRF as “mgmtintf”.
• NXOS: Default VRF is known as “default” and management VRF as “management”.

8. Modularity:

• IOS: Some versions of IOS offer modularity (IOSXE and IOS XR).
• NXOS: It’s a modular operating system (each process runs as a separate process on the system and is separate from others).

9. Virtual Device Contexts:

• IOS: Does not support Virtual Device Contexts (VDCs).
• NXOS: Supports Virtual Device Contexts, allowing partitioning of a single physical device into multiple logical devices.

10. Default Switchport Mode:

• IOS: Default mode is dynamic auto.
• NXOS: Default mode is access.

11. Spanning Tree Protocol:

• IOS: Default is PVST+ (Per VLAN Spanning Tree Plus).
• NXOS: Default is RapidPVST+.

12. Switchport Trunk Encapsulation:

• IOS: Supports both ISL and 802.1Q, and you must specify which one to use before enabling trunking.
• NXOS: Supports only 802.1Q.

13. Command Alias:

• IOS: Does not support command alias by default.
• NXOS: Supports creating alias commands.

14. Python Scripting:

• IOS: Python scripting is not supported (although it is supported in the more recent IOSXE).
• NXOS: Python scripting is supported.

15. Configuration Synchronization:

• IOS: Does not support configuration synchronization.
• NXOS: Supports configuration synchronization between devices for improved consistency and error reduction.


• IOS: Not all devices support ERSPAN (Encapsulated Remote Switched Port Analyzer).
• NXOS: Supports ERSPAN.

17. Object Groups:

• IOS: Typically used in firewall configurations.
• NXOS: Object groups can be used in various configurations, increasing efficiency and reducing repeated commands.

18. System Resources:

• IOS: Automatically allocates resources.
• NXOS: Resources can be manually allocated per module using the system resources command.

19. Control Plane Policing:

• IOS: Uses Control Plane Policing (CoPP) to protect the Control plane against excessive traffic.
• NXOS: Uses Control Plane Policing (CoPP) and also Control Plane Protection (CPPr) for more granularity.

20. Access Control Lists:

• IOS: Extended ACLs use the `accesslist` command from 100199.
• NXOS: There is no specific range for extended ACLs.

21. TimeBased ACLs:

• IOS: Supports timebased ACLs.
• NXOS: Does not support timebased ACLs.

22. DHCP Configuration:

• IOS: Uses `service dhcp` command to enable DHCP service.
• NXOS: DHCP is enabled by default.

23. Unicast Reverse Path Forwarding (uRPF):

• IOS: Configured on an interface with the `ip verify unicast source reachablevia` command.
• NXOS: Configured using a policy map and then applying to an interface.

24. Syslog Messages:

• IOS: Default timestamp includes milliseconds.
• NXOS: Default timestamp does not include milliseconds.

25. Quality of Service (QoS):

• IOS: MQC (Modular Quality of Service CLI) is used to create QoS policies.
• NXOS: Similar to MQC but also allows direct configuration under the interfaces.

Please note that this list is not exhaustive and the features supported may vary between different hardware models and software versions within both NXOS and IOS families. Always refer to the official documentation for specific features on specific devices.