OSFP details that is esay to ignore:

OSFP details that is esay to ignore:
1, Passive interface will not send hello packet, therefore will not form adjacency to any other router. But subnet that attached to this interface will be advertized inside OSPF
2, SPF calcuateion within the area will be triggered only when there is changes of type1 and type2 LSA in the update. Type1 and type2 LSA will only be exchanged within the area.
3, ABR is the router that at least has one interface connecting to backbone area, the the other one to the other area. ABS will generate 2 self type1 LSA, one is for Backbone type1 LSA, the the other is type1 LSA for the other area which ABR connects to.
4, OSPF uses a reference bandwidth of 100 Mbps for cost calculation. The formula to calculate the cost is reference bandwidth divided by interface bandwidth. For example, in the case of Ethernet, it is 100 Mbps / 10 Mbps = 10. Note: If ip ospf cost cost is used on the interface, it overrides this formulated cost. take reference bandwidth of 100mbps, any interface that greater or equal to 100mbps will have the same cost 1 becuase no fraction is allowed.So the OC-3, FastEthernet and GigabitEthernet will all have an OSPF cost of “1” given the default reference bandwidth.
5, With ‘default-information orignate’ command generate ASBR a default route into ospf area but only if there is a default route exited already in its routing table
6, In Cisco configuraiton, use “area x range” for net summary in ABR, and “summary-address …”in ASBR for external route summary. OSPF DOES NOT perform auto-summarizatio.


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