Hello my friend,

Today topic of the network programmability is popular. There is a quite pragmatic approach behind this popularity, which is to lower the operational costs of the network and increase its agility. By agility I mean the way how we create the network services, which time we spend on it and so on. Let’s evaluate how model-driven configuration can help us to do it for Nokia SR OS 16.0.

Brief description

Why have I mentioned SR OS version 16.0? Because model-driven CLI is available starting from SR OS 16.0.R1, which was released some days ago (beginning of June 2018). Actually, it’s one of the very important introductions of this the release in direction of network programmability.

The idea of model-driven CLI (shortly MD-CLI) is very straightforward: to have a single configuration approach based on YANG-models for all configuration interfaces:

• CLI
• NETCONF
• gRPC

You remember, some time ago, we were configuring Nokia (Alcatel-Lucent) SR OS and Cisco IOS XR using NETCONF/YANG (link). We did some reverse engineering activities to rebuild the structure of YANG models directly from the router, though it was possible to read original YANG packages. One of the reasons for that was different structure (or at least not clear relations) between CLI configuration model and YANG data mode. This is something MD-CLI overcomes.

There are some new features, what makes life of the configurator easier, which we’ll review in this article.

What we are going to test?

We’ll review new MD-CLI (model-driven CLI), which is available in Nokia SR OS starting from version 16.0.R1. We aren’t configuring any particular technologies and so on, but we rather focus on CLI itself.

Software version

The following infrastructure is used in my lab:

• CentOS 7 with python 2.7.
• Ansible 2.5.2
• Nokia VSR 16.0.R1 (NEW!)

See the previous article to get details how to build the lab

Nokia VSR 16.0.R1 is the current latest version of VSR, which has been released in the beginning of June 2018.

Topology

As we aren’t configuring particular technologies, there is no particular topology. New VSR is just connected to the management network and is reachable over SSH:

No initial configuration is provided as Nokia VSR has default configuration.

Deployment of Nokia VSR 16.0.R1

The deployment of VM with Nokia VSR 16.0.R1 is just the same as it was for VSR 15.0. You can either read some information about manual deployment or you can use our VNF onboarding tool with small modifications. If you are familiar with Ansible, you can easily update it.

Usage of MD-CLI

When we are logged into newly deployed Nokia VSR 16.0.R1 router, we see just standard CLI, nothing new

Let’s briefly check the version of our Nokia VSR:

Having checked that VSR has correct version, we can enable MD-CLI mode, which is disabled by default. To do that we need to enter the following two commands, logout and log in back to the CLI:

As you might see after re-login the CLI looks in a bit different way. Let’s check what is available from the commands in the top level of MD-CLI by default:

Most of the commands are familiar to you, but there are some new like “edit-config” and “quit-config”

What are the changes then? Let’s review them one by one.

#1. Candidate config

Long ago we have shown the possibility to use candidate config option for previous releases of Nokia SR OS. Now it’s mandatory in MD-CLI. So we need to enter the “edit-config” mode, before we can do anything and by the end of the configuration we’ll need to commit changes in order they are implemented. Let’s try to test without new command:

The message is self-explanatory, so we enable configuration mode:

#2. Watching into existing config

Now we are able to configure something. But before we start configuration, we can review the existing configuration using new structure:

The output of Info will depend on the role that user has. As we are using default “admin” with unlimited rights, we can see everything.

To show running configuration from any user, there is another new command:

This command was introduced instead of “admin display-config” used in classic CLI.

It’s also possible using “info detail” to see the default values, which are configured and not shown normally:

You might spot that there are some a lot of commands starting with “##” symbol. It shows the command, that might exist in certain configuration context, but it isn’t configured currently. On the one hand it gives you additional possibility to see, where you need to configure something; on the other hand you don’t need to guess anymore, if there is implicit (default) value is configured or nothing is configured.

There is also possibility to review config file in form of exact commands needs to be issued to get it using keyword “full-context” after “info” command:

This option of “info” output provides you understanding, which commands you need to apply from top-level context to avoid walk between configuration contexts.

#3. Configuration process

Configuration process hasn’t changed, though some commands might be different (really, just minority of the commands). Let’s provision the card to see how it works:

You see that navigation across CLI has changed. Now there is no long string before “#”, which points to configuration context. It’s shown in “[]”, just before the line, where we enter configuration commands.

As I said earlier, all the configuration is done only in candidate mode, that’s why no changes are applied unless we commit them:

Before committing changes, we have possibility to see what is changing in this iteration:

Now we commit changes and review that they are applied:

With bold I’ve highlighted the fact that “*” symbol, which means unsaved changes, are removed after configuration is committed, as we configured in the very beginning, during activation of MD-CLI, auto-save function.

#4. Configuration commands’ sequence doesn’t matter any more

In previous versions of Nokia SR OS, even if we use candidate mode (link), there were some problems, if the sequence of the commends aren’t correct. With SR OS 16.0.R1 this problem is solved:

As you see, the sequence isn’t correct, as I’m assigning port to the interface before I really configure port to use dot1q encapsulation and before I in general provision corresponding MDA.

Moreover, due to further adaptation of YANG models, the command to configure IPv4 address on interfaces has changed to distinguish each component of IP addresses, which is highlighted by first bold entry. The second bold entry also shows changes to activation of context using “admin-state” comparing to previous “shutdown / no shutdown” construct

Now, when we have entered commands in false order, let’s try to apply them to see, if it works correct:

When we see the commands to be applied using “compare” functions, the commands are already in correct order. So there is no problem, when we issue commit.

#5. Switching to classic CLI

Even if we have activated MD-CLI and we are in MD-CLI mode, we have possibility to switch to classic CLI view and/or just call commands from that mode.

To call the command from another CLI mode just use “//” before the command:

In order to switch to another CLI mode, again, just use “//” without any further command:

Besides informational message, the console definition changes from “[] admin@VSR#” to ordinary “VSR#”, what we have in previous versions.

Lessons learned

As you have seen, some commands have changed. That’s why we would need to learn new commands, if we want to configure MD-CLI manually. But I’d say it makes sense to learn new command and config structure, as it will make easy development of network automation scripts and modules, using NETCONF/YANG model.

Conclusion

The network operations is typically quite rigid to introduction of new CLI modes, as they have learned a lot previous commands and have scripts build to utilize them. But in this case Nokia introduces possibility to switch back from MD-CLI to classic CLI, so the migration is easier and smoother comparing to “make-and-break” approach having only one CLI mode. I personally find new MD-CLI more logical from data model prospective and useful due to mandatory “candidate” mode and compare option. Take care and good bye!

P.S.

If you have further questions or you need help with your networks, I’m happy to assist you, just send me message. Also don’t forget to share the article on your social media, if you like it.

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BR,

Anton Karneliuk