Nonstop forwarding with OSPFv2 and OSPFv3
On a Nonstop OSPFv2 router, failover of a MM does not result in the OSPF v2 router being removed from the OSPFv2 domain. A restart request is sent by the Nonstop OSPFv2 router to the neighboring OSPFv2 routers, after which the graceful restart process begins. This behavior applies to OSPFv3 as well.
A graceful restart allows an OSPF routing switch to stay on the forwarding path while being restarted. The routing switch sends “grace LSAs” that notify its neighbors that it intends to perform a graceful restart. During the configurable grace period, the restarting switch’s neighbors continue to announce the routing switch in their LSAs as long as the network topology remains unchanged. The neighbors run in “helper mode” while the routing switch restarts.
Graceful restart will fail under these conditions:
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There is a topology change during the graceful restart period. The helper switches exit helper mode and adjacencies are lost until the restarting switch rebuilds the adjacencies.
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The neighbor switches do not support helper mode.
For more information on OSPFv2 and OSPFv3 graceful restart, see RFC 3623 and RFC 5187.
Enabling nonstop forwarding for OSPFv2
The routing switch must be in ospf context when enabling Nonstop forwarding for OSPFv2. To enable Nonstop forwarding, enter this command.
Syntax
Enables nonstop forwarding for OSPFv2.
The no version of the command disables nonstop forwarding.
The commands must be executed in ospf context.
Default: Disabled
Example of enabling nonstop forwarding for OSPFv2
HP Switch(ospf)# nonstop
Configuring restart parameters for OSPFv2
Syntax
(ospf)# [no] restart interval 1-1800 [strict-lsa-checking]
Specify the graceful restart timeout interval in seconds.
The no version of the command sets the restart parameters to the default values.
Default: Disabled
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interval 1–1800
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The graceful restart timeout interval (grace period) in seconds. Default: 120 seconds
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strict-lsa-checking
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Used in OSFPv2 context to enable or disable strict LSA operation in a network segment for a neighboring router that is attempting a graceful restart. When enabled, this operation halts Helper mode support if a change in LSAs (topology change) is detected during the neighbor’s restart period.
The no form of this command disables strict LSA operation.
Default: Strict LSA operation enabled
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Viewing OSPFv2 nonstop forwarding information
To display the status of Nonstop forwarding information, enter the show ip ospf general command.
Example of output showing status of nonstop forwarding for OSPFv2
(HP_Switch_name#) show ip ospf general
OSPF General Status
OSPF protocol :enabled
Router ID :10.10.10.80
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.
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Nonstop forwarding : Enabled
Graceful Restart Interval : 500
Graceful Restart Helper Mode : Enabled
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.
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Enabling nonstop forwarding for OSPFv3
The routing switch must be in ospf3 context when enabling Nonstop forwarding for OSPFv3. To enable nonstop forwarding, enter this command.
Syntax
Enables nonstop forwarding for OSPFv3.
The no version of the command disables nonstop forwarding.
The commands must be executed in ospf3 context.
Default: Disabled
Example of enabling nonstop forwarding for OSPFv3
HP Switch(ospf3)# nonstop
Configuring restart parameters for OSPFv3
Syntax
(ospf3)# [no] restart interval 1-1800 [strict-lsa-checking]
Specify the graceful restart timeout interval in seconds.
The no version of the command sets the restart parameters to the default values. Default: Disabled
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interval 1-1800
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The graceful restart timeout interval (grace period) in seconds. Default: 120 seconds
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strict-lsa-checking
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Used in OSFPv3 context to enable or disable strict LSA operation in a network segment for a neighboring router that is attempting a graceful restart. When enabled, this operation halts Helper mode support if a change in LSAs (topology change) is detected during the neighbor’s restart period.
The no form of this command disables strict LSA operation.
Default: Strict LSA operation enabled
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Viewing OSPFv3 nonstop forwarding information
To display the status of Nonstop forwarding information, enter the show ipv6 ospf3 general command.
Example of output showing status of nonstop forwarding for OSPFv3
(HP_Switch_name#) show ipv6 ospf3 general
OSPFv3 General Status
OSPFv3 protocol :enabled
Router ID :10.10.10.80
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.
.
Nonstop forwarding : Enabled
Graceful Restart Interval : 500
Graceful Restart Helper Mode : Enabled
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