Ch.9: Advanced OSPF Flashcards
What formula do you use to calculate OSPF cost?
Interface cost = Reference BW / Interface BW (bps)
What is the default reference bandwidth for OSPF? What does this mean for higher interface speeds?
Default reference BW: 10^8 (100,000,000)
This means that all links faster than 100Mbps have a cost of 1
What is a potential negative impact of increasing the OSPF reference bandwidth?
Lower speed links may no longer be differentiated
Which command would adjust the reference bandwidth to a higher value?
(At the OSPF process)
> auto-cost reference-bandwidth [mbps]
This is only local to each router.
How would you adjust an interface’s OSPF cost? What is the advantage of this?
(At the interface configuration)
> ip ospf cost [1-65535]
Gives a high-level of control over an interface’s cost
What is an OSPF passive interface? How do you set it?
A passive interface will stop sending/receiving OSPF hello packets
(At the router OSPF configuration level)
> passive interface [interface-id]
(To enable for all interfaces)
passive-interface default
Where would you use a passive interface configuration?
On interfaces where you do not want an OSPF adjacency to be set
How do you inject a default route in an OSPF network?
On the uplink ASBR:
(In the router OSPF configuration)
> default-information originate
How would you configure interarea route summarization?
(In the router OSPF configuration)
> area [area-id] range [ip-address] [mask] [advertise | not advertise] [cost cost]
How would you configure summarization for external routes being summarized by an ASBR?
(In the router OSPF configuration)
> summary-address [ip-address] [mask] [not-advertise] [tag tag] [nssa-only]
What OSPF filtering option could you use to prevent an ABR from creating certain type 3 summary LSAs?
The filter-list command can be used to stop the ABR from creating a type 3 LSA for certain subnets.
This way the internal network can still have
