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Technical Configuration Example
Feature Automation Script—
enable-primary-nexthop.slax, enable-alternate-nexthop.slax
Automatically switch between the primary and alternate next hop based on the ping result returned from a
remote host.
Juniper Networks, Inc.
1194 North Mathilda Avenue
Sunnyvale, CA 94089
USA
408-745-2000
www.juniper.net
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Table of Contents
enable-primary-nexthop.slax, enable-alternate-nexthop.slax
1
Description................................................................................................................... 1
System Requirements .................................................................................................. 1
What it Does ................................................................................................................ 1
Set Up .......................................................................................................................... 1
How to Run .................................................................................................................. 3

iii
enable-primary-nexthop.slax, enable-alternate-nexthop.slax
Description
Use real-time performance monitoring (RPM) to automatically use an alternate next-hop
path to reach a remote host when it becomes unreachable, and re-establish the original
path when the remote host becomes reachable again.
System Requirements
All platforms; JUNOS Software 9.3 and above.
What it Does
When a device has been pingable for the last few tries and then the ping test fails, a script
is triggered that enables an alternate next hop for the device, temporarily disabling the
interfaced associated with the primary next hop to the not-pingable device. When the ping
test is again successful, the temporary next hop is disabled and the original route is
re-established.
Set Up
1.
Copy the scripts enable-primary-nexthop.slax and enable-alternate-nexthop.slax to
/var/db/scripts/event directory on the router.
2.
Use a text editor to create two configuration sections: one for the real-time monitoring
of the target address, and one for the event-related configuration to enable the next
hop.
Description

1
: enable-primary-nexthop.slax, enable-alternate-nexthop.slax
a.
For the RPM-related configuration, create and save the configuration shown
below. In the area marked EDIT HERE, enter the valid IP address that can be
pinged as the target address. This is the address for which you will have the
system enable the primary or alternate next-hop routes as needed.
services {
rpm {
probe icmp-ping-probe {
test ping-probe-test {
probe-type icmp-ping;
target address 10.63.0.50; /* EDIT HERE */
test-interval 60;
}
}
}
}
b.
For the event-related configuration, create and save the configuration shown
below. In the areas marked EDIT HERE, enter the name of the primary next-hop
interface that will be enabled or disabled based on the ping test event.
event-options {
policy enable-primary-nexthop {
events ping_test_completed;
within 60 {
trigger on 1;
}
within 120 events ping_test_failed;
then {
event-script enable-primary-nexthop.slax {
arguments {
next-hop-interface <interface-name>; /* EDIT HERE */
}
output-filename foo;
destination foo;
}
}
}
policy enable-alternate-nexthop{
events ping_test_failed;
within 60 {
trigger on 1;
}
within 120 events ping_test_completed;
then {
event-script enable-alternate-nexthop.slax {
arguments {
next-hop-interface <interface-name>; /* EDIT HERE */
}
output-filename zoo;
destination foo;
}
}
}
destinations {
foo {
archive-sites {
/var/tmp;
}
}
}
}
Set Up

2
: enable-primary-nexthop.slax, enable-alternate-nexthop.slax
3.
Enable the scripts by adding the file statement and script filenames to the [edit
event-options event-script] hierarchy level as shown below. Only superusers can enable
event scripts in the configuration.
[edit event-options event-script]
user@host# set file enable-primary-nexthop.slax
[edit event-options event-script]
user@host# set file enable-alternate-nexthop.slax
4.
Load the configuration information:
a.
Use the text editor to open the configuration file that was created previously, and
copy its contents to the clipboard. Make sure you have copied both configuration
sections, the RPM-related and the event-related.
b.
On the device, enter configuration mode:
user@host% cli
user@host> configure
Entering configuration mode
[edit]
user@host#
c.
Use the load merge terminal command to load the configuration information and
merge it with the current configuration:
[edit]
user@host# load merge terminal
[Type ^D at a new line to end input]
> Paste the contents of the clipboard here <
d.
At the prompt, past the contents of the clipboard.
e.
Press Enter.
f.
Press Ctrl+D.
g.
Commit the configuration:
[edit]
user@host# commit and-quit
How to Run
Once the scripts and configurations have been loaded, the script
enable-alternate-nexthop.slax is launched upon event ping_test_failed—when the remote
destination was pingable in the last few tries and is not pingable in the latest try. The next
hop for the default route is added as dl2.0 and the interface passed to this script as an
argument is disabled.
How to Run

3
: enable-primary-nexthop.slax, enable-alternate-nexthop.slax
The script enable-primary-nexthop.slax is launched upon event ping_test_completed—when
the remote destination was not pingable in the last few tries and now is pingable in the
latest try. The next hop for the default route is added, the interface is passed as an
argument to it, and that interface gets enabled.
How to Run