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First look of Open NX-OS

Cisco NX-OS is the network operating system that is used in Cisco Nexus switches. These Nexus switches from Cisco are built for DATA-CENTERS. In this post I will give you a brief idea regarding the NX-OS operating system.  NX-OS has been evolved from SAN-OS which was originally developed for MDS switches by Cisco only. These MDS switches are used for storage network.

Cisco NX-OS is purely based on Micro-kernel Linux where as traditional Cisco IOS is also based on Linux but with Monolithic kernel. I will tell you the difference between these two types of kernel below in this post because it is the key difference between NX-OS and IOS.

 Monolithic Kernel :

Monolithic kernel is a single large process running entirely in a single address space or memory space. It is a single static binary file. All kernel services exists and executes in the kernel address space. If one process having some problem then it will effect all other processes and may interrupt the complete kernel flow. As an example, let's  suppose in IOS if OSPF process having some problem then it will effect all other processes and it may lead your router to hang or restart. You may have experienced it already that sometimes in such cases after restarting the router everything runs fine.

In Monolithic kernel you can not start or restart single service as you have to restart the complete device. Have you ever restart BGP or STP process in Cisco IOS ? Is there any command for it ? NO...

Micro-kernel Linux :

In Micro-kernel , kernel is divided into smaller services. These services run in their separate/individual memory spaces. As they are running in separate memory space one service does not impact other service. This is like different VMs(virtual machines) in Vmware. One VM does not impact other VM. You can also restart or shutdown single service in case of some error. In NX-OS, you can shutdown OSPF service and start BGP service by "Feature-set" command. In NX-OS , Cisco call "service" as a "Module"

Using above description, NX-OS provide these following plus features than IOS :

Molecularity :

Modules or services are loaded into kernel only when needed. These modules can be loaded and unloaded on demand.

Fault Isolation :

This module provides complete process isolation for NX-OS features and services.


This module is helpful in graceful restart or initialization of processes.

I know most of the Juniper freaks out here say that this is same as JUNOS giggle. Yes it is same as JUNOS. After so many years, Cisco realizes this and developed NX-OS. I don't know why Cisco takes so long to realize this.

For so many years they are shipping this NX-OS in their data-center switch which they call Nexus series switches. Cisco Nexus 2000 , 5000 and 7000 are the example of switches which are running on NX-OS. These switches are high performance switches which are intentionally developed for data-center. They can switch or route massive traffic of data-center with latency of less than 1 ms.

As SDN (Software define network) is evolving day by day and to cop up with this paradigm shift, Cisco is working towards OPEN NX-OS.


Open NX-OS is based on Wind River Linux 5. Now it is possible to run any standard Linux-based application on Cisco Nexus switch. It is open to integrate common third-party configuration management like puppet , Chef etc. and network monitoring software like splunk , nagios etc. directly on Nexus switch itself. In previous versions of NX-OS, every thing is closed.  It means you were not able to access underlying Linux of NX-OS. You can only run commands etc. but in Open NX-OS, Cisco has exposed an access to the linux kernel networking stack, where the switch physical and logical interfaces have representation as a net device and an IP address in the kernel layer. Confuse ? Don't worry , In simple language they have provided access to BASH shell of Linux kernel.

In Open NX-OS, you can access to Bourne - Again Shell (BASH). While using bash commands, one can access and manage the underlying linux system on the device. This provides only glimpse of OPEN NX-OS but I am sure you get the essence. So lets jump into the command prompt of Open NX-OS for now:

Some Glimpse of Open NX-OS :

To access Bash shell in Open NX-OS you need to enable "feature bash-shell" command.
n9k_nx_os(config)# feature
bash-shell              lacp                    pbr                     ssh
bfd                     ldap                    pim                     tacacs+
bgp                     lldp                    private-vlan            telnet
dhcp                    msdp                    privilege               tunnel
eigrp                   nat                     ptp                     udld
evmed                   ntp                     rip                     vmtracker
fabric                  nv                      scheduler               vn-segment-vlan-based
hsrp                    nxapi                   scp-server              vpc
interface-vlan          ospf                    sflow                   vrrp
isis                    ospfv3                  sftp-server             vrrpv3
itd                     password                sla                     vtp
n9k_nx_os(config)# feature bash-shell

To get into Bash shell from normal NX-OS command prompt :
n9k_nx_os(config)# run
run          run-script
n9k_nx_os(config)# run
bash         guestshell
n9k_nx_os(config)# run bash ?
*** No matching command found in current mode, matching in (exec) mode ***
  LINE   The command to execute

n9k_nx_os(config)# run bash

There are few commands which I have tried successfully in BASH Shell of Open NX-OS :

bash-4.2$ ls
bin        etc           isan_lib.img  lib64     modflash    root      usbslot2  vdc_12  vdc_4
boot       home          isan_lib_ro   linuxrc   nfsroot     rpms      usr       vdc_13  vdc_5
bootflash  init          isan_lib_rw   log       nginx       sbin      usr.img   vdc_14  vdc_6
cgroup     isan          lc            logflash  nginx_1_fe  slot0     usr_ro    vdc_15  vdc_7
data       isan_bin.img  lcimages      media     nxos        smack     usr_rw    vdc_16  vdc_8
debug      isan_bin_ro   lc_ro         mgmt      opt         sys       var       vdc_17  vdc_9
debugfs    isan_bin_rw   lc_rw         mnt       proc        tmp       vdc_10    vdc_2   vmachine
dev        isanboot      lib           mod-1     rd          usbslot1  vdc_11    vdc_3   volatile

bash-4.2$ free
             total       used       free     shared    buffers     cached
Mem:      12282348    4530196    7752152          0      46500    1766136
-/+ buffers/cache:    2717560    9564788
Swap:            0          0          0

bash-4.2$ uname -a
Linux n9k_nx_os 3.4.43-WR5.0.1.13_standard #1 SMP Thu Aug 27 14:35:24 PDT 2015 x86_64 GNU/Linux

bash-4.2$ yum
yum yum-updatesd yumdownloader
bash-4.2$ yum
RPM-GPG-KEY-puppetlabs RPM-GPG-KEY-reductive.1
RPM-GPG-KEY-puppetlabs.1 puppetlabs-release-pc1-cisco-wrlinux-5.noarch.rpm
RPM-GPG-KEY-reductive puppetlabs-release-pc1-cisco-wrlinux-5.noarch.rpm.1
bash-4.2$ yum

You are thinking now that how can I get this Open NX-OS access ? Right ? Don't worry soon I will publish new post regarding this.

Output of "Show version" of OPEN NX-OS :

n9k_nx_os# show version
Cisco Nexus Operating System (NX-OS) Software
TAC support:
Copyright (c) 2002-2015, Cisco Systems, Inc. All rights reserved.
The copyrights to certain works contained herein are owned by
other third parties and are used and distributed under license.
Some parts of this software are covered under the GNU Public
License. A copy of the license is available at

  BIOS: version
  NXOS: version 7.0(3)I2(1)
  BIOS compile time:
  NXOS image file is: bootflash:///nxos.7.0.3.I2.1.bin
  NXOS compile time:  9/3/2015 16:00:00 [09/04/2015 00:18:15]

  cisco NX-OSv Chassis
  Intel(R) Xeon(R) CPU E5-4667 v3 @ 2.00GHz with 12282348 kB of memory.

  Device name: n9k_nx_os
  bootflash:    3509454 kB
Kernel uptime is 0 day(s), 0 hour(s), 39 minute(s), 3 second(s)

Last reset
  Reason: Unknown
  System version:

  Core Plugin, Ethernet Plugin

Active Package(s):

Output of "Show version" of traditional NX-OS :

NX-OS_Sw1# show version
Cisco Nexus Operating System (NX-OS) Software
TAC support:
Copyright (c) 2002-2014, Cisco Systems, Inc. All rights reserved.
The copyrights to certain works contained herein are owned by
other third parties and are used and distributed under license.
Some parts of this software are covered under the GNU Public
License. A copy of the license is available at

  BIOS:      version 2.1.0
  loader:    version N/A
  kickstart: version 7.0(1)N1(1)
  system:    version 7.0(1)N1(1)
  Power Sequencer Firmware:
             Module 1: version v4.0
             Module 2: version v4.0
  Fabric Power Sequencer Firmware: Module 1: version v3.0
  Microcontroller Firmware:        version v0.0.0.15
  QSFP Microcontroller Firmware:
             Module 2: v2.0.0.0
  SFP Microcontroller Firmware:
             Module 1: v1.3.0.0
  BIOS compile time:       02/24/2014
  kickstart image file is: bootflash:///n6000-uk9-kickstart.7.0.1.N1.1.bin
  kickstart compile time:  3/19/2014 14:00:00 [03/20/2014 08:25:34]
  system image file is:    bootflash:///n6000-uk9.7.0.1.N1.1.bin
  system compile time:     3/19/2014 14:00:00 [03/20/2014 08:27:35]

  cisco Nexus 5672UP Chassis ("Nexus 5672UP Supervisor")
  Intel(R) Xeon(R) CPU  @ 1.80 with 8243416 kB of memory.
  Processor Board ID 

  Device name: NX-OS_Sw1
  bootflash:    8028160 kB

Kernel uptime is 163 day(s), 1 hour(s), 55 minute(s), 43 second(s)

Last reset
  Reason: Unknown
  System version: 7.0(1)N1(1)

  Core Plugin, Ethernet Plugin

This is all I have to introduce about OPEN NX-OS to you guys. Hope you enjoyed my post. Will post more details about the OPEN NX-OS in my future posts. Till then Keep Networking !!!


  1. Nice post!, Everthing was so clear.
    My question is, Will it be possible to Upgrade NX-7ks from actual NX-OS system to the new OPEN-NX-OS?

  2. Thanks for the comment. currently Open NX-OS is in development mode. Soon in future we can upgrade our existing NX-OS to OPEN NX-OS.

  3. very nice post


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