# Unified ISSU Platform Considerations

Unified ISSU is supported on E120 and E320 routers. Unified ISSU is also supported on the ERX1440 router with the SRP-40G PLUS with 2GB of memory. Unified ISSU on the ERX1440 requires a license key.

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.

For information about modules supported on the ERX1440 router:

- See ERX Module Guide, Table 1, ERX Module Combinations for detailed module specifications.
- See ERX Module Guide, Appendix A, Module Protocol Support for information about the modules that support unified ISSU.

Redundant SRP modules are required for unified ISSU support.

Unified ISSU is not supported on the ERX7xx models, the ERX1410 router, and the ERX310 router.

| Note: In JunosE Release 11.3.0, the design enhancements for reenabling CSR FPGA upgrades are implemented, which enables you to perform a stateless upgrade (non-unified ISSU method, with router-wide outage for users) from JunosE releases numbered lower than Release 11.3.0 to JunosE Release 11.3.0. However, you cannot run a unified ISSU procedure from JunosE releases that do not contain the design changes for CSR FPGA functionality (earlier than Release 11.3.0) to JunosE releases that contain the enhanced CSR FPGA design (Release 11.3.0 and later releases), if the router chassis contains ES2 10G LMs or REV-02 ES2 10G LMs. In releases numbered lower than Release 11.3.0, you could not perform either a conventional upgrade or a unified ISSU process on ES2 10G LMs that contained the CSR FPGA upgraded image. You could only download the image from serial Programmable Read-Only Memory (PROM), which was a factory image. If your network contains routers installed with LMs other than ES2 10G LMs or REV-02 ES2 10G LMs, a preferred suggestion is to transfer subscribers configured on the ES2 10G LMs or REV-02 10G LMs to other LMs available in your environment when you perform unified ISSU. This transfer of subcribers to other LMs avoids disruption of user sessions owing to the limitation that exists with performing a unified ISSU operation on ES2 10 LMs and REV-02 10G LMs.