JEFF关于OSPF水平分割的回信

Hi!
 
Split horizon is used on distance vector algorithms (rip, eigrp), to prevent a route from being advertised back out an interface in which it was received.  OSPF is not a distance vector algorithm.  A loop free topology is built, and using shortest path, route tables are built within areas.  The DV type behavior is between areas, with type 3 summary lsas.  In some cases, such as with   To prevent ospf type 3 LSAs from being advertised, you could use a filter list, area area-id filter-list prefix prefix-name in|out , and a prefix list.  The "in" keyword filters type 3 lsa from area 0 into the area-id specified.  "out" filters type 3 lsas from the area specified into other areas.   You could summarize the LSAs, which would allow the ABR to advertise a summarized version of the route into the area specified.
 
or, maybe they are wondering more about configuring ospf on nbma networks.  They could be thinking about configuring subinterfaces, which were developed to get around split horizon issues on an NBMA network using a DV algorithm.  Maybe they are thinking about getting all the link state information into the database within an area, and are thinking of the command IP OSPF NETWORK point-to-multipoint to configure OSPF over a nbma network. 
 
I'd probably want to clarify the interview question, by asking something like: "So, your question is how to enable type 3 LSAs to be advertised back into an area in which the route exists in the topology table?", which shows the interviewer that you know about how OSPF works, you could then tell them what you know.  Maybe by asking the question, you'll better understand what the interviewer is trying to ask.
 
Good luck!