(This post will be replacing the subnetting post in my sticky threads up top the blog)
I pulled this topology from my older posts when I took a deep dive into the world of LSA’s, how to read the Topology table like a laundry list and under stand it, and what type of routers did what.
First I want to list links that are absolutely vital to read and understand for exam day, as you will run into questions regarding these in some fashion or another, and then I will sticky this post up top so the links are available there as well:
EIGRP Distribute-List / Prefix-List configuration – https://loopedback.com/2017/05/10/eigrp-deep-dive-into-prefix-list-configurations-access-list-vs-prefix-list-using-prefix-lists-to-filter-eigrp-routes-with-distribute-lists/
I could keep adding posts to that list all day, as they are pretty important, but you need to have a solid understanding of VPN Types and Tunnel Modes (and what they do), LSA Types and Database understanding, the IPv6 material and knowing how to configure and apply Prefix-Lists, etc. I’d say read all my posts, but I wrote them and my mind still slips on the materials!
Now I pulled this explanation of the LSA types from an older post where I summarized them using the Topology above, so I will paste these into this post, and sticky this thread up top for visibility and move on to the next topic for review!
So first, I will start with a description of each LSA type of the 7 of them:
- LSA Type 1 “Router” – “Router Link States” will be its header in the LSA DB, and the name is self explanatory, these LSA’s are generated by each router with updates on its local Link States, all router types generate and flood this LSA Type.
- LSA Type 2 “Network” – “Net Link States” are only generated and sent by DR’s and BDR’s to routers in the Same Area, that are also on the same multi-access network type, LSA type stays within its own Area, only seen in NON-Point-to-Point network types
- LSA Type 3 “Summary” – “Summary Net Link States” has nothing to do with summarization, but floods its summary of networks from one Area into others except for the Area it is part of – Not flooded into Total-Stub’d Areas (Stub or NSSA)
- LSA Type 4 “Summary ASB” – “Summary ASB Link States” LSA type is only created by ABR’s back to the ASBR, so when redistribution is configured on the ASBR Router it flips a bit in its “Router LSA” (Type 1!), and the ABR(s) then create LSA type 4’s to pass along throughout the network giving OSPF neighbors the path back to the ASBR – Not flooded into Stub Areas.
- LSA Type 5 “Autonomous System External Link State” – or “AS External Link States” in the OSPF LSA DB, these are your “O E1” and “O E2” Redistributed routes, generated from the ASBR itself OUTSIDE an NSSA Area – Not flooded into Stub Areas.
- LSA Type 6 – Not needed for the CCNP ROUTE, but it is for Multicast Extensions of OSPF (MOSPF), but again is not referenced in the the ROUTE exam, just wanted to mention for the sake of thoroughness
- LSA Type 7 “NSSA LSA’s” – This type of LSA is generated by the ASBR INSIDE an NSSA Area does Redistribution, as Type 5 Redistribution LSA’s cannot enter an NSSA Area
Phew. So to cover what type of routers create which type of LSA’s ONE MORE TIME:
- Type 1 – All Routers
- Type 2 – All DR’s
- Type 3, 4 – All ABR’s
- Type 5 – ASBR’s OUTSIDE the NSSA Areas (NSSA’s don’t allow LSA type 5)
- Type 6 – Reserved for MOSPF
- Type 7 – ASBR’s INSIDE the NSSA Areas (Type 7 LSA’s [N1, N2 in route table])
If you don’t fully understand LSA’s, please review Part 1, 2, and 3 of the OSPF LSA posts linked above as this is crucial to exam success if you get some OSPF questions!