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I want to say thank you, I am bluffed by how you have explained that, I have purchased many of CCNA & CCNP courses, but no one has explained it the way you did. Thank you
I have been searching for almost 7 years to know what is the LSA Types differences and their nonsense theory and you nailed it in a shot. Superb. It feels like no instructor knows what exactly LSA's are except you.
Sorry to be that person but there are actually 11 types of LSAs (OSPF). LSA Type 1 Router LSA LSA Type 2 Network LSA LSA Type 3 or 4 Summary LSA & ASBR LSA LSA Type 5 Autonomous System External LSA LSA Type 6 Multicast OSPF LSA Type LSA Type 7 Defined for Not-So-Stubby-Areas LSA Type 8 External Attribute LSA for BGP LSA Type 9,10,11 Opaque LSA RFC 5250 back in 2008 discusses these. Cisco, one, it not the largest, vendor which many people are familiar with, only supported 1-5 for the longest but other vendors supported OSPF LSAs (6-11) well before especially with the advent of Traffic Engineering (10-11 "Opaque" LSAs). Very good explanation on the 5 types you discussed here.
Thank you very much. I really appreciate your explanation with moving diagrams. I currently prepare myself for an exam and it was really hard for me to imagine how it works just out of the slides. Before this video I didn't even understand where the LSA are all send to.
Ed, you're a bit of a savant. I will never understand how you can have such a grasp of all of this. Your instruction is fantastic, I will have to review this when I'm not half asleep, but what you share with us is AMAZING.
Only a few days away from my CCNA, and your videos have helped explain some topics I was murky on after jeremy & david B's courses. You dont have a Security+ course do you?
Noted about BGP, Randy. As for EIGRP, I wrote three EIGRP articles you might enjoy: EIGRP Explained : www.practicalnetworking.net/stand-alone/eigrp-terminology/ EIGRP Metric : www.practicalnetworking.net/stand-alone/eigrp-metric/ EIGRP Feasibility Condition: www.practicalnetworking.net/stand-alone/eigrp-feasibility-condition/
Thank you for your great work, just one remark regarding type 4/5 LSA, you mentioned that router 6 (which is an ASBR) introduced itself to router 4 by type 1 LSA, assuming that this type 1 LSA will be forwarded by the ABR R2 as a type 3 LSA to other areas, so other areas will know about R6, so there will be no need for Type 4 LSA as a helper for this redistributed type 5 LSA !!
>> assuming that this type 1 LSA will be forwarded by the ABR R2 as a type 3 LSA This isn't entirely correct. The actual Type 1 LSA will not be forwarded. Instead, only specific information from _within_ the Type 1 LSA is forwarded -- specifically _only the IP Subnets contained in the Type 1 LSA are forwarded._ The Routers identity (which is included in Type 1 LSAs) is not included in the Type 3 LSAs. To really understand it, I'd recommend the LSA Deep DIve videos: Type 1 & 2: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-1FOBkIoDbCc.html Type 3: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-8fFtU5W9WGk.html
Thanks for both contributions. I'd like to make a remark about LSA type 5 that originates from an external non-OSPF domain in an NSSA area. Shouldn't it be converted from type 7 to type 5?
So glad you found these helpful, Huy. Cheers =) If you're willing... Could you do me a favor? Do you mind sharing this video on Linked In, Reddit, Twitter, Facebook, or any other social media you use? As an independent creator, that would be an _enormous_ help, and I would appreciate it _greatly_ .
Hi! I belive, that you missed one important moment about Type 2 LSAs. When you using Ethernet ports on touter (and nowadays you will mostly use Ethernet) routers by default will treat this links as multiaccess, because they can't know do this link connects directly to another router, or there can be switch in beetwen and potentially multiple routers. So, if you only connect two routers by Ethernet link directly to each other - they will treat this link as multiaccess, chose DR and BDR and will send Type 2 LSAs. You need to explicitly configure this links as p2p.
@ 2:52, if R2 and R3 are then configured with OSPF, would not Hello Packets, DBD, LSR, ... to form adjacency have happen? The forming of the adjacencies must take place with R2 and R3 before L1's can be sent. I can see how LSU/LSAs would be sent upstream from R1, or after adjacencies have already formed. Could you tell me what I am missing? What is the transition from creating full adjacencies between two OSPF routers and when LSA types begin to fully operate. Thanks!
Yes, all that would still happen. I'm simplifying that out in this video to focus on LSAs. But everything else in the series still applies (hello packets, LSU/LSR/LSA/DBD, neighbor adjacency sequence, and so on)
Why is R6’s Type 1 LSA / subnet that is sent to R4 not then sent to area 0 / R1 by R2 via a Type 3 LSA (if a type 3 is summarizing all the Type 1&2’s sent within its area) at which point it would know how to reach R6 when trying to get to the external subnet?
why did the area 0 and area 55 did not knew about router 6 through type 3 summary LSA, assuming R4 to be DR, would Type 3 LSA not have the knowledge to reach R6? that R4 can share with area 0 and then area 55, am missing something?
Many thanks. One question about example with 3 Routers R1,R2,R3 starting approx at 2:30, you mention that there's only 1 LSA type 1 per router (and update if necessary). When R3 emits its LSA type 1, in order for R2 to be aware of R3 update, I guess R1 propagates the update with a LSU (?), is it correct ? i am confused for now, with the propagation mechanism in order for all routers in area 0 to have the same LSDB.
Have a doubt at 11th minute of the video about type 4 LSA, R6 will introduce it to R4 by type 1 LSA, and these will be shared to area 0 via R2 as type 3 LSA, so Routers in R1 will knows about R6 right?
No sure to understand why there is no TYPE 2 LSAs on the 2 segments between R1and R2, and between R1 and R3 since there is also a DR on each link (this after minute 4). Arent these also multi-access links?
@10:56, it is stated that R6 has introduced itself into Area-44 using a Type-1 LSA. I am missing something here. Are we assuming that R4 and R6 are already neighbors? If so, how does this introduction happen?
Yes, they are already neighbors. The implication is that all routers in the same areas have become neighbors because of their Type 1 LSAs. Of course, normally they would be sending hello packets and validating various attributes, but for this video I'm simplifying and saying all routers in the same area are neighbors.
Hi Ed I don't get why we need type 4 LSA. When router R6 introduced it self in area 44 via type 1 LSA should the ABR router R2 have sent type 3 LSA including subnet 9.9..9.0/24 in the summary into area 0? so every routers how to reach R6.
So if a ASBR router introduces with Type 1 LSA to area 44. Why doesn't that type 1LSA get summerised within Typer 3LSA together with all of the other type 1 and 2 LSA's? Type 4LSA would seem like a owerhead. Im sure im missing some critical detail, can anyone explain?please
It's not the LSA itself that gets summarized by a Type 3. It's the _content of the LSA_ (in particular, the IP Networks contained in the LSA) that gets summarized by the type 3. Type 3 LSAs do not contain any information about the routers in foreign areas.
Yes! If you're building the topology, any of the routers on the multi access segment could be the DR (R2/R7/R8/R9). Itw ill be whichever router wins the DR election (or is the first to be stood up). Details in the DR video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Mi3tNSUjb78.html
If you say that the internal routers are representative of any number of internal routers, how about the ABRs? I've watched several intros to OSPF and they all use just a single ABR between areas which immediately makes be wonder about redundancy. I mean isn't this one of the main reasons to use a routing protocol, resilience to hardware (link or router) failures?
Type 3 LSA appears to be useless! In your example, if routers from area 55 does not know about router 6, then what was this type 3 LSA that they received?
I still don't understand why they created LSA5. They could use LSA1 that ASBR generates anyway to spread external routes. Just put all the external routes that you got via redistribution inside LSA1 and it's done. And you can spread them as normal LSA1. Instead of that they created LSA5 and when they realised that it was unreacheble they also created LSA4. I don't understand. I think I miss something. It looks like for me that they just didn't want to change LSA1. It was simpler to add a couple of more LSAs to handle external routes.
Probably not RU-vid videos, but I did write EIGRP articles you might enjoy: EIGRP Explained : www.practicalnetworking.net/stand-alone/eigrp-terminology/ EIGRP Metric : www.practicalnetworking.net/stand-alone/eigrp-metric/ EIGRP Feasibility Condition: www.practicalnetworking.net/stand-alone/eigrp-feasibility-condition/
