Arista Warrior, 2nd Edition

Chapter 9. Configuration Management

In addition to the normal operations such as write memory, copy run start, and the like, the running configuration in Arista’s Extensible Operating System (EOS) can be managed in a variety of interesting ways. To understand the majority of them, I’d like to begin with the command configure replace.

Configure Replace

Remember that Arista EOS, much like the industry standard CLI, is additive. In other words, if you want to remove a command from the running configuration, you must add a command to negate the existing command. For example, if I have a switch that has the following configuration

Arista(config-if-Et1)#sho active
interface Ethernet1
   no switchport
   ip address 10.10.10.1/24

to remove the IP address, I must add a command to do so:

Arista(config-if-Et1)#no ip address
Arista(config-if-Et1)#sho active
interface Ethernet1
   no switchport

Given this model, for decades the only way to load a completely new configuration on a device was either to carefully negate every existing command (a practical impossibility in most cases, not to mention a recipe for network disruption) or to overwrite the startup-config with something else and reload the device. This is a massively disruptive process that can take a large amount of time depending on the device and configuration in play.

In EOS 4.14, Arista added a new option to the configure command that allows you to replace the running configuration on a live switch. This is a very big deal that doesn’t ...