Failover in Case of a Routing Engine Failure
Graceful Routing Engine switchover (GRES) is supported in case of a Routing Engine failure. A failure of the Routing Engine stops the pgcpd process. When the Junos OS high-availability framework detects the Routing Engine failure, it switches control of the BGF to the pgcpd process on the backup Routing Engine. The pgcpd process stores completed H.248 states, and these states survive a restart or a switchover. After the restart or switchover is completed, the pgcpd process reapplies the states.
Gate Synchronization Procedure
When the IPC connection between the pgcpd process and the services PIC or MS-DPC is being reestablished, a synchronization process restores the previous state of gates, so session and call continuity is achieved. That is, existing calls stay active and voice sessions are not disconnected.
The synchronization process can result in the mismatching of gates. Mismatched gates are handled as follows:
- If the pgcpd process detects gates that exist in the Routing Engine, but are missing in the PIC or DPC, the pgcpd process reinstalls the gates on the PIC or DPC. Existing calls receive service from the PIC or DPC when the synchronization is complete.
- If the pgcpd process detects gates that exist on the PIC or DPC, but not on the Routing Engine, the pgcpd process removes the gates from the PIC or DPC. This removal causes the associated sessions to be closed, and the session resources to be released.
- If the pgcpd process detects gates that exist on the PIC or DPC and on the Routing Engine, but the versions of the gates do not match, the pgcpd process forces the Routing Engine version. Doing so maintains call continuity by making sure that the databases are synchronized, while limiting the effect to existing calls and sessions.
You can control the number of mismatches by configuring the synchronization properties.
