topic Re: OSPF Lsa Type 2 in Routing and SD-WAN

OSPF Lsa Type 2

surendrasinghtanwar667 — Tue, 03 Dec 2024 12:37:41 GMT

Hi, I have a question. If there is a DR, then LSA type 2 will be sent to all other routers, but why is DROTHER also sending individual LSA Type 1? I understand LSA Type 2 a little bit, which is that it is used to obtain the information of the router presented in the same subnet and multicast network.

Re: OSPF Lsa Type 2

MHM Cisco World — Tue, 03 Dec 2024 12:48:26 GMT

If you check opsf db you will see advertiser router IP' without lsa1 this IP is unknown for other router

MHM

Re: OSPF Lsa Type 2

surendrasinghtanwar667 — Tue, 03 Dec 2024 13:07:17 GMT

CAN YOU EXPLAIN ME LSA TYPE 2 FROM SCRACTH BECAUSE I AM NOT ABLE TO UNDERSTAND THIS CONCEPT

Re: OSPF Lsa Type 2

paul driver — Tue, 03 Dec 2024 13:14:40 GMT

Hello

@surendrasinghtanwar667 wrote:

Hi, I have a question. If there is a DR, then LSA type 2 will be sent to all other routers, but why is DROTHER also sending individual LSA Type 1? I understand LSA Type 2 a little bit, which is that it is used to obtain the information of the router presented in the same subnet and multicast network.

If you have DR/BDR then you have a multi access network segment, as such Type 2 LSAs advertise this and It the Drs responsibility to flood these type 2 lsas to all others rrtr on this same segment including rtrs that are DRothers.

Ospf Drothers are also rtrs obviously... and they send their own list on routed links via type 1 LSAs (router LSAs) just like another ospf rtr would do

Re: OSPF Lsa Type 2

paul driver — Tue, 03 Dec 2024 13:16:34 GMT

Hello

@MHM Cisco World wrote:

If you check opsf db you will see advertiser router IP' without lsa1 this IP is unknown for other router

Can you elaborate please , not sure what you mean "IP is unknown" ?

Re: OSPF Lsa Type 2

MHM Cisco World — Tue, 03 Dec 2024 14:14:06 GMT

Router# show ip ospf database asbr-summary
OSPF Router with id(192.168.239.66) (Process ID 300)
                Displaying Summary ASB Link States(Area 0.0.0.0)
	LS age: 1463
	Options: (No TOS-capability)
	LS Type: Summary Links(AS Boundary Router)
	Link State ID: 172.16.245.1 (AS Boundary Router address)
	Advertising Router: 172.16.241.5 <<- this IP
	LS Seq Number: 80000072
	Checksum: 0x3548
	Length: 28
	Network Mask: 0.0.0.0 TOS: 0  Metric: 1

This example of show ospf db' do for all type of lsa and you will see advertiser router IP. This IP is learn from LSA1.

MHM

Re: OSPF Lsa Type 2

surendrasinghtanwar667 — Tue, 03 Dec 2024 13:30:39 GMT

SO TYPE 1 LSA IS ONLY SENDED TO DR ONLY

Re: OSPF Lsa Type 2

paul driver — Tue, 03 Dec 2024 13:59:14 GMT

Hello

@MHM Cisco World wrote:
Router# show ip ospf database asbr-summary

This is incorrect what you are showing there is a type-4 LSA, the command for type 2 LSA is:

sh ip ospf database network

Re: OSPF Lsa Type 2

surendrasinghtanwar667 — Tue, 03 Dec 2024 14:03:26 GMT

Suppose that there are 5 Router. R1 R2 R3 R4 R5 R6 they are in multi access network and R1 AND R2 are DR AND BDR. There is one more router R6 which is not the part of this multi network access which is directly connected to R1 via serial cable so my doubt is either all DROTHER will send their individual LSA TO R6 or all DROTHER Router will send LSA to DR Router and then DR Router will send LSA 2 to R6 for creating complete topology of the entire network. Just clear this question

Re: OSPF Lsa Type 2

paul driver — Tue, 03 Dec 2024 14:11:30 GMT

Hello
Correct to the all DR routers mc address 224.0.0.6., in turn ONLY the DR will flood it updates to the all ospf routers on 224.0.0.5 mc address

Re: OSPF Lsa Type 2

MHM Cisco World — Tue, 03 Dec 2024 14:14:53 GMT

Apologies

Again you need to refresh your acknowledge.

MHM

Re: OSPF Lsa Type 2

paul driver — Tue, 03 Dec 2024 14:58:50 GMT

Hello

@MHM Cisco World wrote:

Again you need to refresh your acknowledge.

If your suggesting that your previous example of type4 lsa is related with a type 2 then you are mistaken
What you are showing is a external type LSA 4 originated from some ABR rtr advertising a destination of an ASBR located on a rtr in one of those areas.

The OP is querying type 2 LSAs and their functionality in OSPF it has nothing to do with type 4 LSAs and their functionality

So can you explain or any other please what i need to update my knowledge of as would be happy to say i am wrong if that is the case - as in essence that is what these forums are all about?

Re: OSPF Lsa Type 2

MHM Cisco World — Tue, 03 Dec 2024 16:33:52 GMT

Friend I really want to answer you but I have alot of topic need to cover
regarding LSA4 if Router send LSA4 to all routers to use this IP, how other routers know this IP ?
this job of LSA1
each routers advertise LSA1 to declare to all other routers these IP belong to me.
these IP can use for forward address for LSA4 and for other.

sorry again, if I am not answer you you can send me PM

MHM

Re: OSPF Lsa Type 2

paul driver — Tue, 03 Dec 2024 16:35:53 GMT

Hello @MHM Cisco World
i will stipulate this again - a type4 has absolutely nothing to do with a type 2 and i’ve no idea what ypu are talking about in reference to the OP what happens iif there is no muticaess network as such no DR so no type 2 what then?
So apologies I believe your understanding is incorrect not mine however this is open to discussion to the wider audience and i’m happy to be corrected

Edited
in addition you still haven’t explain g why would you show a command for a type 4 lsa when the command for a type 2 lsa exists ?

Re: OSPF Lsa Type 2

paul driver — Tue, 03 Dec 2024 17:10:18 GMT

Hello
so if you have an additional rtr that is directly connected via serial as such then no DR/ DR will it exit between RTR1 and RTR6 - you see a rtr can have various ospf network types running at the same time so even though rtr 1 is DR on one interface it can be a BDR/DRother or just a P2P on another -
as such in your example the the ospf link type will no doubt become a P2P so no type 2 lsas will exist - the rtr wi just exchange lsa type1/2 unless either rtr is also an abr/asbr etc..

Re: OSPF Lsa Type 2

Cristian Matei — Tue, 03 Dec 2024 16:52:41 GMT

Hi,

First, i'd say is important to clarify LSA Type 1 vs. LSA Type2, when we speak about OSPFv2. Each router will always send one LSA Type 1 per area, advertising all of its links, link type, associated prefix and cost within that area. Additionally, for each network segment where there is DR election, DR will advertise one LSA Type2, which contains all routers attached to that network segment and the network mask of the prefixes attached to that network segment.

To your given example, where R1 is the only router connected to R6, assuming all links are part of same area, R1 will be the router flooding all Type 1 LSA's as well as Type 2 LSA to R6.

Cristian.

Re: OSPF Lsa Type 2

paul driver — Tue, 03 Dec 2024 17:11:39 GMT

Hello @Cristian Matei
thanks for the sanity check.

Re: OSPF Lsa Type 2

surendrasinghtanwar667 — Thu, 05 Dec 2024 04:47:40 GMT

This is the topology where two transit area are there so according to this topology when i check the ospf LSDB Database then i am able to see all router LSA Type 1in R1 LSDB. So my question was that if all routers are sending LSA type 1 to each other so what is the use case of LSA TYPE 2 and why it is being used.

One more question is in transit area or multiaccess area type 2 lsa is generated so what information is shared with DR on that time does all DROTHER router share LSA type 1 information to DR and that information is being shared in the form of lsa type 2 .