How to Use RPCs and Operational Mode Commands in Op Scripts

Using RPCs in Op Scripts

To use an RPC in a SLAX or XSLT op script, include the RPC in a variable declaration, and then invoke the RPC using the jcs:invoke() or jcs:execute() extension function with RPC variable as an argument. The jcs:invoke() function executes the RPC on the local device. The jcs:execute() function, in conjunction with a connection handle, executes the RPC on a remote device.

The following snippet, which invokes an RPC on the local device, is expanded and fully described in Example: Customize Output of the show interfaces terse Command Using an Op Script:

XSLT Syntax

<xsl:variable name="rpc">
    <get-interface-information/> # Junos RPC for the show interfaces command
</xsl:variable>
<xsl:variable name="out" select="jcs:invoke($rpc)"/>
...

SLAX Syntax

var $rpc = <get-interface-information>;
var $out = jcs:invoke($rpc);

The following snippet invokes the same RPC on a remote device:

XSLT Syntax

<xsl:variable name="rpc">
    <get-interface-information/> # Junos RPC for the show interfaces command
</xsl:variable>
<xsl:variable name="connection" select="jcs:open('198.51.100.1', 'bsmith', 'test123')"/>
<xsl:variable name="out" select="jcs:execute($connection, $rpc)"/>
<xsl:value-of select="jcs:close($connection)"/>
...

SLAX Syntax

var $rpc = <get-interface-information>;
var $connection = jcs:open('198.51.100.1', 'bsmith', 'test123');
var $out = jcs:execute($connection, $rpc);
expr jcs:close($connection);

In Python op scripts, RPCs are easy to execute using Junos PyEZ APIs. Each instance of the Junos PyEZ Device class has an rpc property that enables you to execute any RPC available through the Junos XML API. After establishing a session with a local or remote device, you can execute the RPC by appending the rpc property and RPC method name to the device instance. The return value is an XML object starting at the first element under the <rpc-reply> tag.

To execute the RPC on the local device, create the Device instance using an empty argument list. To execute the RPC on a remote device, create an instance of Device using the appropriate arguments to connect to that device.

The following code invokes an RPC on the local device and prints the reply:

Python Syntax

from jnpr.junos import Device
from lxml import etree

with Device() as jdev:
    rsp = jdev.rpc.get_interface_information()
    print (etree.tostring(rsp, encoding='unicode'))

The following code invokes the same RPC on a remote device and prints the reply:

Python Syntax

from jnpr.junos import Device
from lxml import etree
import jcs

user = jcs.get_input('Enter username: ')
password = jcs.get_secret('Enter user password: ')

with Device(host='198.51.100.1', user=user, password=password) as jdev:
    rsp = jdev.rpc.get_interface_information()
    print (etree.tostring(rsp, encoding='unicode'))

To execute an RPC on a remote device, an SSH session must be established. In order for the script to establish the connection, you must either configure the SSH host key information for the remote device on the local device where the script will be executed, or the SSH host key information for the remote device must exist in the known hosts file of the user executing the script. For each remote device where an RPC is executed, configure the SSH host key information with one of the following methods:

• To configure SSH known hosts on the local device, include the host statement, and specify hostname and host key options for the remote device at the [edit security ssh-known-hosts] hierarchy level of the configuration.

• To manually retrieve SSH host key information, issue the set security ssh-known-hosts fetch-from-server hostname configuration mode command to instruct Junos OS to connect to the remote device and add the key.

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  user@host# set security ssh-known-hosts fetch-from-server router2
  The authenticity of host 'router2 (198.51.100.1)' can't be established.
  RSA key fingerprint is 30:18:99:7a:3c:ed:40:04:0f:fd:c1:57:7e:6b:f3:90.
  Are you sure you want to continue connecting (yes/no)? yes
  Warning: Permanently added 'router2,198.51.100.1' (RSA) to the list of known hosts.

• To manually import SSH host key information from a file, use the set security ssh-known-hosts load-key-file filename configuration mode command and specify the known-hosts file.

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  user@host# set security ssh-known-hosts load-key-file /var/tmp/known_hosts
  Import SSH host keys from trusted source /var/tmp/known_hosts ? [yes,no] (no) yes

• Alternatively, the user executing the script can log in to the local device, SSH to the remote device, and then manually accept the host key, which is added to that user’s known hosts file. In the following example, root is logged in to router1. In order to execute a remote RPC on router2, root adds the host key of router2 by issuing the ssh router2 operational mode command and manually accepting the key.

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  root@router1> ssh router2
  The authenticity of host 'router2 (198.51.100.1)' can't be established.
  RSA key fingerprint is 30:18:99:7a:3c:ed:40:04:0f:fd:c1:57:7e:6b:f3:90.
  Are you sure you want to continue connecting (yes/no)? yes
  Warning: Permanently added 'router2,198.51.100.1' (RSA) to the list of known hosts.

Displaying the RPC Tags for a Command

You can display the RPC XML tags for operational mode commands in the CLI of the device. To display the RPC XML tags for a command, enter display xml rpc after the pipe symbol ( | ).

The following example displays the RPC tags for the show route command:

user@host> show route | display xml rpc 
<rpc-reply xmlns:junos="http://xml.juniper.net/junos/10.1I0/junos">
    <rpc>
        <get-route-information>
        </get-route-information>
    </rpc>
    <cli>
        <banner></banner>
    </cli>
</rpc-reply>

SLAX and XSLT scripts can execute RPCs using the RPC XML tags. Python scripts must convert the RPC tags and command options into a format suitable for Python. For more information about using Junos PyEZ to execute RPCs and about mapping RPC tags to the corresponding Python method and method arguments, see Using Junos PyEZ to Execute RPCs on Devices Running Junos OS.

Using Operational Mode Commands in Op Scripts

Some operational mode commands do not have XML equivalents. SLAX and XSLT scripts can execute commands that have no XML equivalent using the <command> element. Python scripts can execute these commands by using the Junos PyEZ cli() method defined in the Device class.

If a command is not listed in the Junos XML API Operational Developer Reference, the command does not have an XML equivalent. Another way to determine whether a command has an XML equivalent is to issue the command followed by the | display xml command, for example:

user@host> operational-mode-command | display xml

If the output includes only tag elements like <output>, <cli>, and <banner>, the command might not have an XML equivalent. In the following example, the output indicates that the show host command has no XML equivalent:

user@host> show host hostname | display xml
<rpc-reply xmlns:junos="http://xml.juniper.net/junos/10.0R1/junos">
    <output>
       ...
    </output>
    <cli>
        <banner></banner>
    </cli>
</rpc-reply>

user@host> show services cos statistics forwarding-class | display xml
<rpc-reply xmlns:junos="http://xml.juniper.net/junos/8.3I0/junos">
    <cli>
        <banner></banner>
    </cli>
</rpc-reply>

SLAX and XSLT op scripts can include commands that have no XML equivalent. Use the <command>, <xsl:value-of>, and <output> elements in the script, as shown in the following code snippet. This snippet is expanded and fully described in Example: Display DNS Hostname Information Using an Op Script.

<xsl:variable name="query">
    <command> 
        <xsl:value-of select="concat('show host ', $hostname)"/>
    </command>
</xsl:variable>
<xsl:variable name="result" select="jcs:invoke($query)"/>
<xsl:variable name="host" select="$result"/>
<output>
    <xsl:value-of select="concat('Name: ', $host)"/>
</output>
...

Python op scripts can execute commands that have no XML equivalent by using Junos PyEZ APIs. The cli() method defined in the Device class executes an operational mode command and returns the output in text format. For example:

from jnpr.junos import Device

def main():

    with Device() as jdev:
        res = jdev.cli('show host hostname', warning=False)
        print (res)

if __name__ == "__main__":
    main()

You can also specify format='xml' to return the output formatted as Junos OS XML elements. For more information about the Junos PyEZ cli() method, see http://junos-pyez.readthedocs.org/en/latest/_modules/jnpr/junos/device.html#Device.cli .