Configuring OSPF GR

This section describes how to configure OSPF GR to avoid traffic interruption and route flapping caused by the active/standby switchover.

Prerequisites

Before configuring OSPF GR, complete the following tasks:

Configuring IP addresses for interfaces to ensure that neighboring routers are reachable at the network layer.
Establishing the OSPF Neighbor Relationship.

Context

To avoid traffic interruption and route flapping caused by the active/standby switchover, you can enable OSPF GR.

After the OSPF process is restarted through Graceful Restart (GR), the Restarter and the Helper reestablish the neighbor relationship, exchange routing information, synchronize the LSDB, and update the routing table and forwarding table. These operations ensure the fast convergence of OSPF and the stability the network topology.

In practical applications, you can configure OSPF GR on the dual main control boards to avoid service forwarding from being affected by the fault occurred on the main control board.

Procedure

Access the system view.
```
system-view
```
Access the OSPF process view.
```
ospf [ process-id ]
```
Enable the opaque-LSA function.
```
opaque-capability enable
```
Opaque LSAs provide a generic mechanism for OSPF extension:
- OSPF supports GR using Type 9 LSAs.
- OSPF supports TE using Type 10 LSAs.
Before configuring OSPF GR, you must enable opaque LSA capability running the opaque-capability enable command.

When enabling or disabling the opaque LSA function, OSPF process will go down in order to renegotiate the new capability, which means that the traffic will be affected for few seconds.
Enable the OSPF GR function.
```
graceful-restart
```
After the graceful-restart command is run to enable GR for a FW, the Helper function is also enabled.
Set GR session parameters.
```
graceful-restart [ period period | planned-only | partial ] ^*
```
- Set period, the GR period on the Restarter is set. By default, the restart time is 120 seconds.
- Set planned-only, the Restarter supports only the planned GR. By default, the Restarter supports both the planned GR and unplanned GR.
- Set partial, the Restarter supports the partial GR. By default, the Restarter supports the totally GR.
Configure GR session parameters on the Helper.
1. Configure the local router to enter the Helper mode only after neighbors pass the filtering policies of the IP prefix or ACL.
  graceful-restart [ period period | partial | planned-only ] ^* helper-role { ip-prefix ip-prefix-name | acl-number acl-number }
2. Configure the Helper not to check the LSAs outside the AS (AS-external LSA).
  graceful-restart [ period period | partial | planned-only ] ^* helper-role ignore-external-lsa
  
  By default, the Helper checks the LSAs outside the AS.
3. Configure the Helper to support only the planned GR.
  graceful-restart [ period period | partial | planned-only ] ^* helper-role planned-only
  
  By default, the Helper supports both the planned GR and unplanned GR.
  
  To configure multiple parameters at the same time, run the graceful-restart [ period period | partial | planned-only ] ^* helper-role { { { ip-prefix ip-prefix-name | acl-number acl-number } | ignore-external-lsa | planned-only } ^* | never } command.