Junos OS Evolved ensures all nodes in a system are running the same software version.
If you insert an RE that has the same current software version as the primary RE into the system, the new RE joins the system, and the configurations and the other software versions automatically synchronize from the existing RE to the new RE, even if you have not configured the auto-sw-sync statement.
If you insert an RE that has a different software version into the system and you have not configured the auto-sw-sync enable statement, the RE is kept outside the system and the system generates a software mismatch alarm. The alarm message displays the RE name and the version of software on the newly-inserted RE, similar to the following: Software Version Mismatch on re1:junos-evo-install-ptx-x86-64-20.4R2.6-EVO..
user@host-re0> show system alarms 2 alarms currently active
Alarm time Class Description
2021-04-19 16:02:26 PDT Major Re1 Node unreachable
2021-04-19 16:04:46 PDT Major Software Version Mismatch on re1:junos-evo-install-ptx-x86-64-20.4R2.6-EVO
To clear the alarms and bring the RE into the system, manually synchronize the primary RE to the new RE with the request system software sync all-versions operational mode command.
We recommend that you configure the auto-sw-sync enable configuration statement at the [edit
system] hierarchy level before inserting a new RE into the system. When you do so, the RE in the system detects the newly-inserted RE and automatically synchronizes the software to the new RE. All images are synchronized to the new RE and the system reboots the inserted RE. When the newly-inserted RE comes back up, it joins the system. Each software image has the configuration used when the image ran stored with it. The configuration associated with the current running image is
synchronized from the primary RE to the backup RE. Configurations stored with the rollback and other images are also synchronized to the backup RE when you configure the auto-sw-sync enable statement on the primary RE.
To replace an RE in a dual-RE system:
1. Configure the auto-sw-sync enable statement.
Enter configuration mode, configure the auto-sw-sync enable statement, commit the configuration, and exit configuration mode to get back to operational mode:
user@host-re0> edit
user@host-re0# set system software auto-sw-sync enable user@host-re0# commit
commit complete user@host-re0# exit user@host-re0>
2. Replace the RE.
3. Allow several minutes for the software and configurations to synchronize and for the newly-inserted RE to reboot.
4. Verify that the newly-inserted RE is now part of the system and that the software versions on both REs are the same, by issuing the show system software list operational mode command.
You must make sure that the system has finished synchronizing all of the images in the background before you switch control to the newly-inserted RE to ensure that the newly-inserted RE does not remove any images from the existing RE.
user@host-re0> show system software list [...output truncated...]
---node: re0
---Active boot device is primary: /dev/sda List of installed version(s) :
'-' running version
'>' next boot version after upgrade/downgrade '<' rollback boot version
- junos-evo-install-ptx-x86-64-20.4R2.13-EVO - [2021-05-05 09:19:16]
< junos-evo-install-ptx-x86-64-20.4R2.14-EVO - [2021-05-05 09:03:23]
---node: re1
---Active boot device is primary: /dev/sda List of installed version(s) :
'-' running version
'>' next boot version after upgrade/downgrade '<' rollback boot version
- junos-evo-install-ptx-x86-64-20.4R2.13-EVO - [2021-05-05 09:22:09]
< junos-evo-install-ptx-x86-64-20.4R2.14-EVO - [2021-05-05 09:06:50]
5. If the software was not automatically synchronized or if you decided not to configure the auto-sw-sync enable statement, manually auto-sw-synchronize the software versions and configurations to the newly-inserted RE, by issuing the request system software sync all-versions operational mode command from the primary RE.
All software images and configurations stored with the images are synchronized to the new RE and the new RE is rebooted. When the new RE comes back up, it joins the system.
6. (Required if you have a rescue configuration) Synchronize the rescue configuration from the primary RE to the secondary RE with the file copy rescue-config-filename secondary-re-name:/config/
command on the primary RE.
For a dual-RE system, when the secondary RE boots with a different current image than the primary RE's current image and the auto-sw-sync enable statement is configured, the primary RE
synchronizes the current image to the secondary RE. The primary RE also synchronizes the rollback software image and the other images to the secondary RE. If the current configuration file
(juniper.conf.gz) from the primary RE matches the current configuration file on the secondary RE, then the primary RE does not synchronize the rescue configuration (rescue.conf.gz) to the secondary RE. For example:
user@host-re0> file copy /config/rescue.conf.gz re1:/config/
7. Verify that the newly-inserted RE can function properly with the request chassis routing-engine master release operational mode command on the primary RE to release control to the newly-inserted RE.
If the newly-inserted RE then does not become the primary RE, issue the request chassis routing-engine master release command on the inserted RE to release control, remove the newly-inserted RE, get a different RE and insert it, and repeat this procedure.
For more information about node synchronization, see "request system software sync" on page 211 and
"auto-sw-sync" on page 164.