NXOS vs IOS

Owned by Vasileios Bouloukos (Unlicensed)
Last updated: Feb 17, 2018

NX-OS is the operating system of the Cisco Nexus  Series switches. NX-OS unifies L2 classic and lossless Ethernet switching and storage switching in one operating system. NX-OS is a Linux-based, next-generation operating system with high availability, modularity, resiliency, and serviceability at its foundation. NX-OS is highly attuned to data center applications and designed to support a unified fabric. Based on the industry-proven Cisco SAN-OS software, NX-OS facilitates continuous availability and sets the standard for mission-critical data center environments. The self-healing and highly modular design of NX-OS makes zero-impact operations a reality and enables excellent operational flexibility.

There are key differences that should be aware of a Network Engineer who is familiar with the CISCO IOS. The most important are highlighted below:

  • NX-OS uses a feature-based license model. Features such as vPC and Fibre Channel over Ethernet (FCoE) can be enabled via the feature configuration command. Configuration and verification commands are not available until the specific feature has been enabled.For instance, I have a Nexus 7k switch with the basic license scheme and I need to configure BGP. In this case, I will need to order and install the LAN_ENTERPRISE_SERVICES_PKG. Then, it would be possible to activate the BGP feature and configure BGP.
  • NX-OS supports VDCs only for Nexus 7000 platforms. This capability enables a physical device to be partitioned into logical devices. The default VDC is used when you log in for the first time.
  • By default Secure Shell version 2 (SSHv2) is enabled and Telnet is disabled.
  • The default login administrator user is admin and it is not possible to login anymore with just a password. In particuar, the Cisco IOS supports login to a network device e.g. via telnet or ssh by providing just a single password (not username). Now, the NX-OS does not support this option and you have to provide username AND password to login (e.g. via telnet or ssh) to the device. 
  • NX-OS uses a kickstart image and a system image. The kickstart image provides the Linux kernel and the system image provides the Layer 2/3 functionalities and features such as OTV, DHCP etc.
  • All Ethernet interfaces are called Ethernet. The FastEthernet, GigabitEthernet, TenGigabitEthernet interface naming convention no longer exists.
  • EtherChannel (IOS) name convention has been replaced by Port-Channel (NX-OS).
  • The Write memory command is no longer available and has been replaced with the copy running-config startup-config.
  • Show commands can be executed identically from both the exec and config mode.
  • Show commands have parser help even in configuration mode.
  • Slash (forward-slash) notation supported for all IPv4/IPv6 masks. For instance

In any case the NX-OS alias command syntax can be used to create an alias for a shortcut. For instance it is possible to still use the "write" IOS command in NX-OS to save the running configuration.