Hi ninja
Just to elaborate on what your excerpt says, the ABR creates Type 3 LSA's to summarize the routes within its area. Type 3 LSA's are flooded by ABR's into the backbone where other ABR's can pick them up.
Type 4 LSA's describe REACHABILITY to ASBR's (autonomous system boundary routers, which connect to other AS's).
Type 5 and 7 LSA's are originated by ASBR's to describe routes external to the AS. (Type 5 is the usual external route LSA, Type 7's are generated by an ASBR in a "not-so-stubby area." The NSSA area's ABR will translate a Type 7 LSA into a Type 5 before advertising it into the backbone.
Whether the Type 5 gets accepted into other areas depends whether the area is a stub area.
Whether the Type 3 gets accepted into other areas depends whether the area is a totally stubby area.
So,
Type 3 LSA
-summarizes routes WITHIN an area
-created and advertised by an ABR
-flooded to the backbone
-will not be accepted into a TOTALLY STUBBY area
Type 4 LSA
-describes a route to an ASBR
-created by the ABR of the area where the ASBR is located
-flooded to the backbone
-will not be accepted into stub or totally stubby areas
Type 5 LSA
-can originate only in a non-stub area that contain an ASBR
-describes route to a destination outside the AS
-created by ASBR and flooded throughout area
-flooded by ABR into the backbone
-will not be accepted into stub or totally stubby areas
Type 6 LSA's are not supported by Cisco
Type 7 LSA
-originate only within a Not-So-Stubby Area
-NSSA is an area that doesn't allow external routes but still contains an ASBR (nice going)
-created by the ASBR in the NSSA area and forwarded to the ABR (NOT flooded within the NSSA)
-flooded by the ABR into the backbone
-will not be accepted into stub or totally stubby areas
Hope this helps - please rate the post if it does.
