This article explains the setup where the user is trying to poll SNMP to a loopback IP in inet where the external physical interface is in a virtual router. This solution also hold good for SRX in packet mode
Your setup might look like the following:
In the current setup, the SNMP client is connected to an external interface ge-0/0/0 which is in a custom virtual router, and the client is trying to do SNMP polling on a loopback interface (lo0.1) which is in a default routing instance (inet.0).
ICMP, Telnet, and SSH will work from the SNMP client to lo0.1, but SNMP polling will not work. This setup is currently not supported and might give unpredictable results.
Clients from routing instances other than the default can access MIB objects and perform SNMP operations only on the logical system networks to which they belong. Clients from the default routing instance can access information related to all routing instances and logical system networks.
Also see the following: Understanding SNMP Support for Routing Instances .
2020-07-14: Article reviewed for accuracy; no changes required.