I finally got it. It helps if you draw a picture of what is happening. Below is a message from Eric McMasters author of Routing Exam Cram. He summarized it for me. I hope this helps someone. BTW, 100% positive some part of this will show on the test. Thanks again Eric!!! Look at it as a big picture. First you have your AS. Within this AS you have multiple areas. Your intra-area routes are routes that are only passed within a single area. Intra-area routes (LSA's 1 and 2) are the only routes that are allowed in a totally stubby area. To gain access outside of the area in a totally stubby setup routers have to use a default route from the ABR. Intra-area routes do not go beyond the boundaries of the area itself. Inter-area routes (LSA's 3 and 4) advertise routes outside of the area. This allows a router in area 1 to know about a route in area 4. These inter-area routes do not go beyond the boundaries of the AS. Now your external routes (LSA 5) are routes that come from an external AS or another protocol that is being redistributed into OSPF. These routes are propagated across the entire network unless a stub, totally stub, or nssa are configured. If this is the case the type 5 LSA's are stopped at the ABR. Even by creating a "redistribute static subnets" or a "redistribute connected" command under the OSPF process these routes will be treated as External routes (Type 5 LSA's) and will be propagated across the entire network. Now for a brief breakdown of the stub, totally stubby, and nssa areas and how they operate. With a stub area you are allowing inter and intra area routes (Type 1-4 LSA's). This will allow a router to know of a specific route in another area along with specific routes in his own area. These are good because it blocks Type 5 LSA's at the ABR, which are always flooded across a network. For a router to gain access to route via another process or a route that is being redistributed it will need to use a default route that is provided by the ABR. With a totally stubby area you are limiting the types of routes that are propagating the area. In this case you are only allowing intra-area routes (Types 1-2 LSA's). This is means that routers only know of routes within their specific area. If they need to get to another area they will have to use the default route that is provided by the ABR. Now the most confusing is the NSSA or Not-So-Stubby-Area. According to the rules of OSPF an area can not be a stub or totally stub area if a router in that area is an ASBR (Autonomous System Boundary Router). An ASBR is a router that connects two different AS's or a router that is "redistributing" anything under the OSPF process. You have the option of creating a NSSA, which is similar in function to a stub area in that it allows Type 1-4 LSA's, but it converts the Type 5 LSA's that are being created by the ASBR into Type 7 LSA's. The Type 7 LSA's are converted back to Type 5's at the ABR. The other option is to create a totally NSSA which is similar to the totally stubby area, but only allows Type 1-2, and 7 LSA's. I know that this is probably more that what you were looking for as far as an answer to your question, but knowing which LSA's are used for what makes the whole OSPF process easier to understand. For more on LSA's and OSPF in general I would recommend that you go to the Cisco website and do a search on "OSPF Design Guide". This design guide has some very useful information and can help in understanding OSPF operation. You can also do a search on "OSPF LSA types" and find out more on the OSPF LSA operation and functions. Hope that I didn't overload you and that you found some of this information useful. Thanks. **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associates.html _________________________________ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
