OSPF Virtual Link issue - behavior of example is not being replicated

[helcio]

  Hi to everybody.

  My question takes as starting point the example shown in:

  https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/47866-ospfdb7.html

  I'm trying to build that example in GNS3. 

  Straight to the point: in my topology, Router 1.1.1.1 doesn't advertise a Type 3 LSAs related to prefix 12.0.0.0/8 (which it learned through the virtual link) in Area 1. Neither Router 3.3.3.3 advertises a Type 3 LSA related to prefix 4.0.0.0/8 (which it learned through the virtual link) in Area 1.

   Am I missing something?

   Thanks in advance.

   PS: I've attached an image of topology for purpose of clarification

[MHM Cisco World]

 can i show routing table of ARB between Area 0 and Area 1?

[Georg Pauwen]

Hello,

not sure what you are missing. Based on the topology diagram you have posted, make sure your configs look like below:

R1

interface Ethernet2/0/0
ip address 4.0.0.1 255.0.0.0
!
interface Serial2/1/0
ip address 5.0.0.1 255.0.0.0
!
router ospf 1
router-id 1.1.1.1
network 4.0.0.0 0.0.0.255 area 0
network 5.0.0.0 0.0.0.255 area 1
area 1 virtual-link 3.3.3.3

R2

interface Serial0/1/0
ip address 5.0.0.2 255.0.0.0
!
interface A1/0/20
ip address 6.0.0.2 255.0.0.0
!
router ospf 1
router-id 2.2.2.2
network 5.0.0.0 0.0.0.255 area 1
network 6.0.0.0 0.0.0.255 area 1

R3

interface Ethernet0/0
ip address 12.0.0.3 255.0.0.0
!
interface A2/0.20
ip address 6.0.0.3 255.0.0.0
!
router ospf 1
router-id 3.3.3.3
network 6.0.0.0 0.0.0.255 area 1
network 12.0.0.0 0.0.0.255 area 2
area 1 virtual-link 1.1.1.1

[helcio]

   Hi, Georg.

   Let me be more specific. The first image shows the adaptation that I've made to example cited. 

   Please, take a look. The question is: why doesn't R1 advertise 3.3.3.0/24 to Area 52 using a Type 3 LSA? It learned about 3.3.3.0/24 from the virtual link. A similar question: why doesn't R3 advertise 1.1.1.0/24 to Area 52 using a Type 3 LSA? It learned about 1.1.1.0/24 from the virtual link.

   The second image shows that those Type 3 LSAs are not created by ABRs. I simply don't know why...

   Below are my OSPF configurations:

---

R1#show running-config | section ospf
router ospf 10
router-id 1.1.1.1
area 52 virtual-link 3.3.3.3
network 1.1.1.1 0.0.0.0 area 51
network 12.12.12.1 0.0.0.0 area 52

---

R2#sh running-config | section ospf
router ospf 10
router-id 2.2.2.2
network 0.0.0.0 255.255.255.255 area 52

---

R3#sh running-config | section ospf
router ospf 10
router-id 3.3.3.3
area 52 virtual-link 1.1.1.1
network 3.3.3.3 0.0.0.0 area 0
network 23.23.23.3 0.0.0.0 area 52

[Georg Pauwen]

Hello,

my OSPF database looks different from yours. Which IOS images are you using in GNS3 ?

[helcio]

   I'm using an image of a Router 7200 Series, Georg. For each one of the routers.

[Georg Pauwen]

Hello,

that could explain it. I am using IOSv versions. Can you post the full configs of your three routers so I can lab this up exactly like you did ?

[helcio]

   Hi, Georg.

   Yes, I can.

---

R1#sh running-config

interface FastEthernet0/0
ip address 1.1.1.1 255.255.255.0

interface Serial1/0
ip address 12.12.12.1 255.255.255.0

router ospf 10
router-id 1.1.1.1
area 52 virtual-link 3.3.3.3
network 1.1.1.1 0.0.0.0 area 51
network 12.12.12.1 0.0.0.0 area 52
---

R2#sh running-config

interface Serial1/0
ip address 12.12.12.2 255.255.255.0

interface Serial1/1
ip address 23.23.23.2 255.255.255.0

router ospf 10
router-id 2.2.2.2
network 0.0.0.0 255.255.255.255 area 52
---

R3#sh running-config

interface FastEthernet0/0
ip address 3.3.3.3 255.255.255.0

interface Serial1/1
ip address 23.23.23.3 255.255.255.0

router ospf 10
router-id 3.3.3.3
area 52 virtual-link 1.1.1.1
network 3.3.3.3 0.0.0.0 area 0
network 23.23.23.3 0.0.0.0 area 52
---

   In addition, I'm attaching an image that show how the topology is displayed in GNS3.

   Thank you for your time, Georg.

   Helcio

[MHM Cisco World]

check R1 and R3 router-id 
show ospf and see router-id for each one

[helcio]

   Hi!

---

R1#sh ip ospf 10
Routing Process "ospf 10" with ID 1.1.1.1

---

R3#sh ip ospf 10
Routing Process "ospf 10" with ID 3.3.3.3

---

   Those are the values that were defined in both configurations... 

[paul driver]

Hello
Based the the first topology you posted - The OSPF VL needs to be created between R1 and R3 and you should see route propagation from area 2 

Based the the second topology you posted - The OSPF VL needs to be created between R1 and R3 and you should see route propagation from area 51 

[paul driver]

Hello

   The second image shows that those Type 3 LSAs are not created by ABRs. I simply don't know why...

R2 should have all received routes as inter-area because all its links are in area 52

R3 is the the backbone rtr and as such has connection to R2 and R3 (VL) so i would say it’s only inter-area route should be area51 prefixes

R1 is now directly connected to the backbone rtr R3 via its VL so its should receive intra-area prefixes 

[helcio]

   Hi, Paul.

   I agree that R2 should have its OSPF entries marked as Inter-Area (IA). No questions about that.

   The fact that R2 does not receive TWO Type LSAs for 1.1.1.0/24 is what surprises me.

   I know R1 advertises 1.1.1.0/24 to Area 52 with cost equals to 1 because it is an ABR now (by mean of the the virtual link). I see that in GNS3, by the way.

   However, I think R3 should have advertised 1.1.1.0/24 to Area 52 as well. Let me explain: R3 learned about 1.1.1.0/24 by receiving a Type 3 LSA from R1 through the virtual link. I see that in GNS3. Because R3 is also an ABR, it should have advertised 1.1.1.0/24 to Area 52 with cost equals to 128. But I don't see that in GNS3. And I don't know why!

   If R2 received those Type LSAs, it would obviously choose that one sent by R2.    

[paul driver]

Hello

---

@helcio wrote:

1.1.1.0/24 to Area 52 with cost equals to 128  

---

Where do you get equal that costing from, R2 will choose the lower cost of the IA route, in this case it would be its serial interfaces(cost 64) + metric of summary lsa

sh ip ospf database summary | in 1.1|Me 

[helcio]

   Yes, I'm taking that into account. R2 has cost equals to 64 to both, R1 and R3.