Breakout is a mechanism to divide a high bandwidth interface into smaller bandwidth interfaces. Cisco Nexus switches support the breakout of high bandwidth interfaces at the module level or at the per-port level. In this lesson we will learn how to Configuring Interfaces Breakout in Nexus.

So, we can split interfaces in two methods. These are-

  • Module Level Breakout
  • Dynamic Breakout

Module Level Breakout:

When we want to breakout a full module, then this is the way to do that. Below command will need to be executed.

interface breakout module < module_number >

Example:
Nexus(config)# interface breakout module 1
Module will be reloaded. Are you sure you want to continue(yes/no)? yes

If you want to revert back, then use no interface breakout module command.

You have to keep in mind, a modular level breakout needs the module reload and all configurations of that particular module will be deleted.

Dynamic Breakout:

This is the method for peer interface breakout. Below command will help to breakout the interface at port level.

interface breakout module {module_no.} port {port_no.} map {new_port_map}

Example:
Nexus(config)# interface breakout module 2 port 1 map 10g-4x

Breakout LAB:

In this LAB we will breakout a 40G interface into 4x10G interface. We are using N9K-C93180LC-EX as our physical hardware.

How to Configuring Interfaces Breakout in Nexus

N9K-C93180LC-EX# show module
Mod Ports             Module-Type                       Model          Status
--- ----- ------------------------------------- --------------------- ---------
1    32   28x40G + 4x40/100G Ethernet Module    N9K-C93180LC-EX       active *

We are using default portmode for this particular model.

N9K-C93180LC-EX# show running-config | i portmode
hardware profile portmode 4x100G+28x40G

Before breakout, here is the “show interface brief” output.

N9K-C93180LC-EX# show interface brief | i Eth1/
Eth1/1        --      eth  routed down    XCVR not inserted          auto(D) --
Eth1/2        --      eth  routed down    XCVR not inserted          auto(D) --
Eth1/3        --      eth  routed down    XCVR not inserted          auto(D) --
Eth1/4        --      eth  routed down    XCVR not inserted          auto(D) --

--- output omitted ---

Before configuring any breakout, it’s recommended to check the release note and configuration guide to know details about limitation or best practices. In this particular model below are the limitations-

For default portmode, if we do 4x10G breakout, then it is supported only on 1,3,5,…,27 port number. And if we breakout, then the corresponding bottom port will be non-operational. For example, if we configure port 1, then port 2 will be non-operational. If we configure port 3, then port 4 will be non-operational.

There is also limitation, if you use other portmodes. So, it is highly recommended to check Cisco nexus configuration guide as reference.

Now, let’s move to the main configuration part.

N9K-C93180LC-EX(config)# interface breakout module 1 port 1,3 map ?
  10g-4x  Breaks out a 40G  high BW front panel port into four 10G ports
  25g-4x  Breaks out a 100G  high BW front panel port into four 25G ports
  50g-2x  Breaks out a 100G high BW front panel port into two 50G ports

N9K-C93180LC-EX(config)# interface breakout module 1 port 1,3 map 10g-4x

So, we are done with the breakout. Let’s verify our new interfaces.

N9K-C93180LC-EX# show interface brief | i Eth1/
Eth1/1/1      859     eth  access up      none                        10G(D) --
Eth1/1/2      859     eth  access up      none                        10G(D) --
Eth1/1/3      859     eth  access up      none                        10G(D) --
Eth1/1/4      859     eth  access up      none                        10G(D) --
Eth1/3/1      859     eth  access up      none                        10G(D) --
Eth1/3/2      859     eth  access up      none                        10G(D) --
Eth1/3/3      859     eth  access up      none                        10G(D) --
Eth1/3/4      859     eth  access up      none                        10G(D) --
Eth1/5        --      eth  routed down    XCVR not inserted          auto(D) --
Eth1/6        --      eth  routed down    XCVR not inserted          auto(D) --
Eth1/7        --      eth  routed down    XCVR not inserted          auto(D) --

--- output omitted ---

Clearly, we can see that, our Eth1/1 interface is now becoming Eth1/1/1-4, and Eth1/3 port into Eth1/3/1-4. So, this is how we do the breakout in nexus.

Written by Rajib Kumer Das

I am Rajib Kumer Das, a network engineer with 7+ years of experience in multi-vendor environment. In my current company, I am responsible to take care critical projects and it's support cases. I do have several vendor certificates and have plans to go further.

This article has 3 comments

  1. Piyal Reply

    It is very helpful to understand, Thanks for the post and keep continue.

  2. Eden Reply

    Configuring breakout on QSFP ports using speed 10000 adds interface breakout module module number port port range map – in the running-config output.

    • Rajib Kumer Das Reply

      Yes, “interface breakout module {module number} port {port range} map {map}” is the command for breakout. But, I didn’t get your point. Please elaborate.

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