12.7.2 Stub router operation
You can use the max-metric router-lsa configuration command to enable stub router functionality at the domain level. You can also specify whether the router functions as a stub router on a permanent basis, or only at startup.
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(1) For normal operation
The router advertises maximum cost for its routes on a permanent basis. It continues to operate as a stub router until the user deletes the setting.
(2) When operating as a stub router after startup
The router advertises maximum cost for its routes when either of the events below occurs. It continues to operate as a stub router until the timer specified in the configuration expires.
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Starting the switch
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After switching the master switch (except when graceful restart is successful)
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After restarting the unicast routing program (except when graceful restart is successful)
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After graceful restart occurs and the Switch has failed to learn a route as a restart router,
You can stop the router from operating as a stub router by executing the clear ip ospf stub-router operation command or removing the setting from the configuration. The following figure shows the operation of a stub router:
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![[Figure Data]](./GRAPHICS/ZU310060.GIF)
(3) Notes
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Do not change the configuration of a stub router that is participating as a helper router in a graceful restart. The stub router might begin or cease operation causing disruption to the helper process.
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If a router is set up to always operate as a stub router and you then change the settings so that it operates as a stub router after startup, it will immediately cease to operate as a stub router.
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You cannot configure a virtual link through a stub router.
If the cost in the transit area is higher than 65535, the virtual link will mark itself as unreachable.
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In the older OSPF standard described in RFC 1247, routing information subject to a maximum metric is not used for SPF computation. For this reason, devices that do not conform to the newer OSPF standard will not register routes through the stub network.