# NSO API using Python

Load **blank.ssh.enabled.cfg**

```
#IOS-XE
config replace flash:blank.ssh.enabled.cfg
 
#IOS-XR
configure
load bootflash:blank.ssh.enabled.cfg
commit replace
```

Create a python script that interacts with NSO’s northbound API.

* The script should create Lo303 on R3 with ip address 30.30.30.30/32
* After creating that loopback, the script should interate through all XE devices and print out each Loopback with its name and IP address.

## Answer <a href="#ed57c6aa-1c45-46a7-bf1e-314253118c94" id="ed57c6aa-1c45-46a7-bf1e-314253118c94"></a>

Create the following python script on the nso server.

```
import ncs

with ncs.maapi.single_write_trans('admin', 'python') as t:
    root = ncs.maagic.get_root(t)
    device_cbd = root.devices.device['r3']
    device_cbd.config.ios__interface['Loopback'].create('300')
    device_cbd.config.ios__interface.Loopback['300'].ip.address.primary.address = '3.3.3.3'
    device_cbd.config.ios__interface.Loopback['300'].ip.address.primary.mask = '255.255.255.255'
    t.apply()


with ncs.maapi.single_read_trans('admin', 'python') as t:
    root = ncs.maagic.get_root(t)
    devices = root.devices
    for device in devices.device:
        if 'ios-cli' in device.device_type.cli.ned_id:
            for interface in device.config.ios__interface.Loopback:
                print(f'{device.name} has loopback {interface.name} with IP {interface.ip.address.primary.address}')
```

<div align="left"><figure><img src="/files/7PQtC79juuyxY8tJdKoM" alt=""><figcaption></figcaption></figure></div>

## Explanation <a href="#id-1cb8dde3-d4d1-808c-8c36-f857515aaeee" id="id-1cb8dde3-d4d1-808c-8c36-f857515aaeee"></a>

First, we need to understand how the loopback interface is accessed in modeled config. This is different than the native IOS-XE config. We have two ways we can see this. One is using “ | display xpath” from NSO:

<div align="left"><figure><img src="/files/zP8NgeFJdsgQKsw95UDL" alt=""><figcaption></figcaption></figure></div>

Another is by staging the config and displaying in XML before aborting.

<div align="left"><figure><img src="/files/zbHiyWACwJnKOhgbVmmZ" alt=""><figcaption></figcaption></figure></div>

This gives us the modeled data for a loopback interface.

First the script starts with the following line, which means to do a single write transaction. The next line gets us to the root of the NCS config database. When opening a transaction, you must at minimum specify the user (’admin’) and the context (’python’, as opposed to CLI, web UI etc). This just allows NSO to audit where the change came from.

```
import ncs

with ncs.maapi.single_write_trans('admin', 'python') as t:
    root = ncs.maagic.get_root(t)
```

Next, we start specifically at device r3 and create the loopback first. We must use the **create()** method. We can’t just assign a new container/list-element using python logic such as **\[’Loopback’]\[’300’] = …**. Instead we need to use **create()** so that NSO can validate the new data against the YANG schema.

```
import ncs

with ncs.maapi.single_write_trans('admin', 'python') as t:
    root = ncs.maagic.get_root(t)
    device_cbd = root.devices.device['r3']
    device_cbd.config.ios__interface['Loopback'].create('300')
```

However, note that while we need to use **.create()** to create a new list, we can use the python **del** to delete a leaf. This is because deleting information does not need to be validated against a YANG schema.

Finally, we add the attributes of the interface (the address and mask). Once the container is created using **create()**, we can add attributes using standard python logic. Using **t.apply()** applies the config (does a commit) within the transaction that we opened.

```
import ncs

with ncs.maapi.single_write_trans('admin', 'python') as t:
    root = ncs.maagic.get_root(t)
    device_cbd = root.devices.device['r3']
    device_cbd.config.ios__interface['Loopback'].create('300')
    device_cbd.config.ios__interface.Loopback['300'].ip.address.primary.address = '3.3.3.3'
    device_cbd.config.ios__interface.Loopback['300'].ip.address.primary.mask = '255.255.255.255'
    t.apply()
```

Next, we use a single read transaction to iterate through all XE devices and print their loopback information. I use an if statement that checks the NED to determine whether this is XE or XR. We’ll see a better way to iterate over a group in the next lab.

```
with ncs.maapi.single_read_trans('admin', 'python') as t:
    root = ncs.maagic.get_root(t)
    devices = root.devices
    for device in devices.device:
        if 'ios-cli' in device.device_type.cli.ned_id:
            for interface in device.config.ios__interface.Loopback:
                print(f'{device.name} has loopback {interface.name} with IP {interface.ip.address.primary.address}')
```


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