the slides here said the default metric after using default-information originate always is 20 but when i try to do this command the result is different
You are correct. The External LSA that carries the default route has a metric (i.e. cost) of “1”…not 20. If you can tell me the name of the course and name of the video within that course where you took this screenshot I’ll ask our video producer’s to insert a note at that point.
As to whether-or-not this makes R1 an ASBR, take a look at the Type-1 Router LSA generated from R1. If that router is an ABR or an ASBR (or both) it will advertise that capability within its Router LSA.
OSPF Router with ID (0.0.0.1) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
0.0.0.1 0.0.0.1 553 0x80000002 0x002F03 5
0.0.0.2 0.0.0.2 600 0x80000002 0x00B087 4
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
0.0.0.0 0.0.0.1 553 0x80000001 0x00357C 1
R1#show ip ospf database router self-originate
OSPF Router with ID (0.0.0.1) (Process ID 1)
Router Link States (Area 0)
LS age: 24
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 0.0.0.1
Advertising Router: 0.0.0.1
LS Seq Number: 80000002
Checksum: 0x2F03
Length: 84
AS Boundary Router
Number of Links: 5
Link connected to: a Stub Network
(Link ID) Network/subnet number: 1.0.0.0
(Link Data) Network Mask: 255.254.0.0
Number of MTID metrics: 0
TOS 0 Metrics: 1
Link connected to: a Stub Network
(Link ID) Network/subnet number: 10.11.1.2
(Link Data) Network Mask: 255.255.255.254
Number of MTID metrics: 0
TOS 0 Metrics: 1
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 0.0.0.2
(Link Data) Router Interface address: 10.1.121.1
Number of MTID metrics: 0
TOS 0 Metrics: 64
Link connected to: a Stub Network
(Link ID) Network/subnet number: 10.1.121.0
(Link Data) Network Mask: 255.255.255.0
Number of MTID metrics: 0
TOS 0 Metrics: 64
Link connected to: a Stub Network
(Link ID) Network/subnet number: 10.1.12.0
(Link Data) Network Mask: 255.255.255.0
Number of MTID metrics: 0
TOS 0 Metrics: 1
i don`t see anything related to default routes on Type-1 router LSA on R1
R1<-.1-----------S1/0---------.2–>R2
10.1.121.0/24
The Type-1 Router LSA from R1 will not show you any information about the default route it generated. That is contained in a Type-5 External LSA. However, your question was if R1 became an ASBR by generating a default route and the output you provided (the Router LSA from R1) does show that is IS advertising itself as an ASBR:
sir, i`m going to ask you a very weird questions :
1-when R1 create a Type 5 external lsa, the default metric value is 20. but why the default metric value is different in the default route(metric=1 by default)?
2-in Type-1 Router LSA, why there is an indication that router is an ABR or an ASBR ?what does that means ?what problems does this behavior trying to solve?
The behavior of setting the default cost of External LSAs to 20…with the exception of the default-route (also contained in an External LSA) which has a cost of 1 is a Cisco thing. Other vendors (like Juniper) don’t use those values. I have no idea why Cisco decided to do it this way.
As to why a Type-1 router LSA contains flags for ABR or ASBR…I also do not know why. I don’t honestly know what purpose this solves since ABRs clearly place their own Router-ID inside of their type-3 Summary LSAs…and ASBRs place their router-ID inside of their Type-5 external LSAs.
Two very good questions for which you may never find an answer. If you do…please let me know.
in this part at the minue 41:15 , you asking yourself a question but i didnt understand that question you were talking about the stub area vs the default-information originate command and you asking yourself this command (quoted exactly like what you said) : "you might be thinking wait a second we just saw when we use the default-information originate command it creates a type 5 external lsa but youre telling me that stub area dont allowed that so how is the abr is going to do it?" sir, what is the meaning of this question?i dont understand your question
what was you mean by "stub area don`t allowed that "?
The purpose of Stub areas (Stub, Totally-Stubby, NSSA and Totally NSSA) is to prevent ABRs from flooding the area with Type-5 External LSAs. But this presents a dilemma because a Type-5 External LSA is created when you issue the command, “default-information originate”.
So in my video I was presenting a question;
How do we get a default route into a Stub area when…
…the command “default-information originate” by design creates a Type-5 external LSA and…
…Type-5 External LSAs are not allowed into Stub Areas
here,R2 is going to stop sending the external default route from R4 and will send a type-3 default route only for all these external routes including the default route.correct ?
Yes, that is correct. When the ABR (R2 in your diagram) is connected to a Stub, Totally-Stubby, or Totally NSSA area that ABR will dynamically generate a default route and inject it within a Type-3 Summary LSA.
If you and I are OSPF routers, after I form an adjacency with you I know what area you are in because that was part of the OSPF Hello packet you sent me. Let’s assume that the link you and I share is in Area-2. If I receive an OSPF Link-State Update packet from you this is what I will do:
If that packet contains any Type-1, Type-2, Type-3 or Type-4 LSAs I will place them into my Area-2 database (because they came from my neighbor in Area-2 and these LSAs are not allowed to be flooded beyond the area in which they originated).
I will then continue to flood those LSAs to any other connected neighbors I have in Area-2
If the Link-State Update packet contains any Type-5 External LSAs I will flood those to all of my neighbors, regardless of what area they are in. This means if I am an ABR with other neighbors in Area-0 and Area-7 I will flood the External LSAs to those neighbors too.
Because Type-5 LSAs are flooded throughout the entire OSPF domain, they don’t belong to any one specific area. That’s why in the output of “show IP ospf database” they are at the end of the output and no area value is associated with them.
but sir that`s totally weird to me because type-7 nssa external lsas are also external routes but as you can see there is area 2 indication here
the type-7 nssa external lsas are not belongs to ospf domain like the type-5 external lsas
Type-7 External LSA do not get flooded throughout the entire OSPF domain like Type-5’s do. Type-7 LSAs, are like Type-1’s through Type-4’s. Once they get originated by an ASBR in Area-X, they must stay in Area-X. In this case, Area-X must be configured as a Not So Stubby Area. That’s why Type-7’s are associated with an area in the output of “sho ip ospf database”.
