Discovering NETCONF RPCs

We've seen in the previous recipes how to use some common RPCs to query system state information on our JUNOS OS devices. But how exactly did we discover the cryptic connection between, for example, the CLI command show route and the RPC equivalent <get-route-information>? The JUNOS OS management daemon, mgd, is responsible for speaking the necessary native protocol to the type of client requesting information: either a human operator on the CLI, or a machine interface via XML. It maps the available system calls to both a CLI and an RPC. In this recipe, we'll explore this mapping.

Getting ready

Ensure you have access to a working JUNOS OS device. You don't necessarily need to have completed the previous recipes on setting up NETCONF remote access.

How to do it...

The steps for the recipe are as follows:

1. Log in to the JUNOS OS device using your normal user credentials and choose the operational mode CLI command that you'd like to work with:

      adamc@router> show arp 
      MAC Address Address Name Interface Flags
      0a:00:27:00:00:00 10.0.201.1 adamc-mac em0.0 none

2. Execute the command, but use the pipe modifier in order to query the XML that maps to the corresponding RPC call:

      adamc@router> show arp | display xml rpc 
      <rpc-reply                
      xmlns:JUNOS="http://xml.juniper.net/JUNOS/15.1F6/JUNOS">
      <rpc>
      <get-arp-table-information>
      </get-arp-table-information>
      </rpc>
      <cli>
      <banner></banner>
      </cli>
      </rpc-reply>

3. Repeat the command, but this time use the pipe modifier in order to explore the XML which maps to the response from the RPC call:

      adamc@router> show arp | display xml 
      <rpc-reply    
      xmlns:JUNOS="http://xml.juniper.net/JUNOS/15.1F6/JUNOS">
      <arp-table-information    
      xmlns="http://xml.juniper.net/JUNOS/15.1F6/JUNOS-arp"    
      JUNOS:style="normal">
      <arp-table-entry>
      <mac-address>0a:00:27:00:00:00</mac-address>
      <ip-address>10.0.201.1</ip-address>
      <hostname>adamc-mac</hostname>
      <interface-name>em0.0</interface-name>
      <arp-table-entry-flags>
      <none/>
      </arp-table-entry-flags>
      </arp-table-entry>
      </arp-table-information>
      <cli>
      <banner></banner>
      </cli>
      </rpc-reply>

How it works...

In step 1, we see the basic command that we're using as a CLI operator.

In step 2, the extra output pipe causes the JUNOS OS management daemon to not actually execute the command, but instead tell us the RPC that it would use if it were executing the command. So, in this case, we can see that it's <get-arp-table-information>, which is the focus of our attention.

In step 3, we get to learn what the likely response from this RPC will be when our automation app makes the RPC call. In this case, the normal tabular format seen by the human is presented to a machine reader, with each of the fields decorated by XML tags. This allows easy and unambiguous interpretation of the response.

There's more...

Using the JUNOS OS | xml rpc modifier is also particularly useful for understanding how to present complicated arguments. In this case, for example, it's possible to see how we filter the output of the show route command (which would ordinarily be large and unwieldy) for a specific destination and table:

      adamc@router> show route table inet.0 1.0.0.1/32 | display xml         
      rpc 
      <rpc-reply  xmlns:JUNOS=" http://xml.juniper.net/  
       JUNOS/15.1F6/JUNOS">
      <rpc>
      <get-route-information>
      <destination>1.0.0.1/32</destination>
      <table>inet.0</table>
      </get-route-information>
      </rpc>
      <cli>
      <banner></banner>
      </cli>
      </rpc-reply>

See also

Juniper make great efforts to document the JUNOS OS XML API. You can find the latest version of their XML API explorer at https://apps.juniper.net/xmlapi. It provides a browser-based explorer of the configuration tags available and the operational mode RPCs available as in the following screenshot:

Figure 1.1 Juniper XML API Explorer