Netgear XCM8810 Chassis User Manual - Page 677
Areas, Configuring Graceful OSPF Restart
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NETGEAR 8800 User Manual able to inform its neighbors in advance that OSPF is restarting. An unplanned restart would occur if there was some kind of system failure that caused a remote reboot or a crash of OSPF, or an MSM/MM failover occurs. As OSPF restarts, it informs its neighbors that it is in the midst of an unplanned restart. You can decide to configure a router to enter graceful restart for only planned restarts, for only unplanned restarts, or for both. Also, you can separately decide to configure a router to be a helper for only planned, only unplanned, or for both kinds of restarts. Configuring Graceful OSPF Restart To configure a router to perform graceful OSPF restart, use the following command: configure ospf restart [none | planned | unplanned | both] Since a router can act as a restart helper router to multiple neighbors, you will specify which neighbors to help. To configure a router to act as a graceful OSPF restart helper, use the following command: configure ospf [vlan [all | ] | area | virtual-link ] restart-helper [none | planned | unplanned | both] The graceful restart period sent out to helper routers can be configured with the following command: configure ospf restart grace-period By default, a helper router will terminate graceful restart if received LSAs would affect the restarting router. This will occur when the restart-helper receives an LSA that will be flooded to the restarting router or when there is a changed LSA on the restarting router's retransmission list when graceful restart is initiated. To disable this behavior, use the following command: disable ospf [vlan [all | ] | area | virtual-link ] restart-helper-lsa-check Areas OSPF allows parts of a network to be grouped together into areas. The topology within an area is hidden from the rest of the AS. Hiding this information enables a significant reduction in LSA traffic and reduces the computations needed to maintain the LSDB. Routing within the area is determined only by the topology of the area. The three types of routers defined by OSPF are as follows: • Internal router (IR)-An internal router has all of its interfaces within the same area. • Area border router (ABR)-An ABR has interfaces in multiple areas. It is responsible for exchanging summary advertisements with other ABRs. • Autonomous system border router (ASBR)-An ASBR acts as a gateway between OSPF and other routing protocols, or other autonomous systems. Chapter 24. OSPF | 677
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