Hardware Requirements for Unified ISSU

The router must support unified ISSU. Therefore the router must be an E120, E320, or ERX-1440 router.
Two SRP modules must be installed in the router.
All installed combinations of line modules and IOAs must support unified ISSU. Unsupported modules that are online are reloaded during the unified ISSU, with consequent loss of connections and traffic forwarding.
Do not install IOAs in the chassis while the unified ISSU operation is in process.
The redundant SRP module must have at least 300 MB of free memory. Depending on their configuration, line modules require up to 75 MB of free memory.

For information about modules supported on E120 and E320 routers:

See E120 and E320 Module Guide, Table 1, Modules and IOAs for detailed module specifications.
See E120 and E320 Module Guide, Appendix A, IOA Protocol Support for information about the modules that support unified ISSU.
On the ERX-1440, certain hardware updates might require a module to be cold restarted. Unified ISSU cannot be successfully accomplished with such modules. In this case, the behavior is the same as for unsupported line modules. The unified ISSU process reboots these modules and holds them down until the supported modules on the router complete the unified ISSU process.
When hardware updates are required for modules that you have installed in an ERX-1440 router, contact your Juniper Networks representative to determine whether the update affects unified ISSU.