Sunday, March 05, 2006
Questions about OSPF facts that play tricks on your memory when you stay away from OSPF for a month.
Here is a post with questions I plan to re-visit once a week and think through to periodically reinforce some basic OSPF concepts that also need some thoughtful memorization. Some of these things like the multicast addresses used by OSPF are a matter of simply remembering things. However some things like the area types into which ABRs will generate default routes by default are a matter of thinking through the motivation behind such behavior to aid in 'smart' memorization. I am planning a separate post later about the latter method of smart memorization.
- How many different types of authentication methods can you use with OSPF?
- What is the default cost of an OSPF virtual link?
- What is the default metric type for an OSPF external route?
- Which kind of LSAs never age out?
- Do you need to visit every router in an area to make a normal area a stub area? How about for a converting a normal area to a totally stubby area? How about if you are just converting a stub area into a totally stubby area?
- Which IP transport protocol does OSPF use?
- What multicast addresses does OSPF use for its advertisements?
- What is the restriction w.r.t area types on areas that can be used by virtual links for transit?
- Which bit in the LSA controls translation of type-7 LSAa to type-5 LSAs? What kind of areas does this translation happen in?
- What kind of areas does OSPF inject default routes into by default?
- Which metric-type has a constant cost as it gets propagated through an OSPF network?
- Given an E1 and and E2 external route to the same prefix, which one would be preferred?
- Under what conditions might an ABR for a NSSA area not translate type-7 LSAs into type-5 LSAs and still be doing the right thing?
- Why might you want an ASBR to inject a default route into an OSPF area even if the ASBR itself did not have a default route? What command would you use to make that happen?
- On an NBMA network, which OSPF network types are RFC-compliant and which are Cisco extensions?
- Which are the OSPF network types for NBMA that need explicit neighbor statements?
- Which are the OSPF network types for NBMA that involve DR/BDR election?
- What is the default cost of external routes redistributed into OSPF?
- Which kind of stub areas are specified in an RFC and which are Cisco extensions?