Special shoutout to Cyber Elite @reaper for his contribution to this blog!
It's considered best practice to create an Out Of Band (OOB) network for the management interfaces of your security appliances and services, so that they cannot be compromised.
But an OOB network can create interesting challenges. Your appliances may need to access resources that are not available on the secured network. One example is Palo Alto Networks' integrated User Identification mechanisms, where either the firewall reads security audit logs on an Active Directory server, or the server gets an agent software installed that does the reading and sends the output back to the firewall. If the AD server is not connected to the secured network, a different route needs to be taken to get that information on the firewall.
For this particular use case, a service route can be configured that redirects connections originating from the management plane, via the backplane, to the dataplane. This will force the outgoing connection to egress from a normal network interface without exposing the management interface (pretty cool, huh?).
To configure a service route:
Navigate to the Device tab on your firewall
Click the Setup section
Go to 'Services'
Find the 'Service Route Configuration' link
Enable the 'Customize' radio button
Scroll down to 'UID Agent' and
Select the new source interface and IP address for these connections
Device > Setup > Services > Service Route Configuration
NOTE: This will work for both the installed UID agent software and the clientless configuration on the firewall.