08-22-2008 09:45 AM - edited 03-03-2019 11:14 PM
Hi NetPros,
In Cisco BSCI Official Exam Certification guide, page 189, the author says that ABR propagate Summary LSAs to other areas through the backbone area. He mentioned only LSA type 3.
Is it the same for LSA type 4?
Here's the excerpt:
"ABR LSA Propagation
When a router is configured as an ABR, it generates summary LSAs and floods them into the
backbone area. Adjacencies within an area are advertised using Type 1 or Type 2 LSAs, and these
prefixes are passed to the backbone using Type 3 summaries. These summaries are then injected
by other ABRs into their own areas (except for totally stubby areas).
External routes and summaries from other areas are received by the ABR and passed back into the
local area."
Solved! Go to Solution.
08-22-2008 10:42 AM
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.
08-22-2008 10:02 AM
No, it's not the same. Type 4 - ASBR-Summary LSA.
Keep reading, it will soon start to make sense. I highly suggest you get a couple of Cisco gear and lab it up. Then it will definitely make sense.
HTH,
__
Edison.
08-22-2008 10:43 AM
After learning about the ABRs and summaries can you now see why all areas must be connected directly or via virtual link to area 0?
08-22-2008 10:42 AM
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.
08-24-2008 07:27 AM
Thanks guys, especially CriscoSystems.
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