OSPF Virtual Link Question

[hhhax7]

Studying for my ROUTE exam and had a practice question yesterday that I am kind of stuck on. Here is a picture of what the topology was like....

https://imgur.com/a/7iGH2CN

Every router ID was it's router number 4 times (R1 = 1.1.1.1, R2 = 2.2.2.2, R3 = 3.3.3.3). The issue is the loopback of R3 was not showing up in the routing table of R1. Obviously it is because R3 needs a virtual link to connect it to Area 0. So I did a show run on R3 and there was already a virtual link configured and it was conifigured as "area 10 virtual link 2.2.2.2". 

Well I know that is wrong because the area you specify needs to be the transit area. So I then issued the following command.......

R3:
conf t
router ospf 1
area 1 virtual link 2.2.2.2

R2:
conf t
router ospf 1
area 1 virtual link 3.3.3.3

When I did this, a "show ip ospf virtual links" told me that the virtual link was "down". The other incorrect virtual link was still in the config, so I did negated it was a "no" and got rid of it on both routers. After doing this, it made no difference, the new virtual link was still down and I could not get the loopback of R3 to show up in the routing table of R1.

Does anyone have any idea how to troubleshoot a down virutal link? I had never run into this before so was very confused. I also just set this up in GNS3 and had no issues getting it to work.

[Georg Pauwen]

Hello,

I cannot tell if R1 and R3 in your drawing are ABRs. Make sure the configs look like below, the VL should work then:

R1

interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface GigabitEthernet0/0
description Link to R2
ip address 10.0.1.1 255.255.255.0
duplex auto
speed auto
media-type rj45
!
router ospf 1
router-id 1.1.1.1
area 1 virtual-link 3.3.3.3
network 1.1.1.1 0.0.0.0 area 0
network 10.0.1.0 0.0.0.255 area 1

R2

interface Loopback2
ip address 2.2.2.2 255.255.255.255
!
interface GigabitEthernet0/0
description Link to R1
ip address 10.0.1.2 255.255.255.0
duplex auto
speed auto
media-type rj45
!
interface GigabitEthernet0/1
description Link to R3
ip address 10.0.2.1 255.255.255.0
duplex auto
speed auto
media-type rj45
!
router ospf 1
router-id 2.2.2.2
network 2.2.2.2 0.0.0.0 area 1
network 10.0.1.0 0.0.0.255 area 1
network 10.0.2.0 0.0.0.255 area 1

R3

interface Loopback3
ip address 3.3.3.3 255.255.255.255
!
interface GigabitEthernet0/1
description Link to R2
ip address 10.0.2.2 255.255.255.0
duplex auto
speed auto
media-type rj45
!
router ospf 1
router-id 3.3.3.3
area 1 virtual-link 1.1.1.1
network 3.3.3.3 0.0.0.0 area 10
network 10.0.2.0 0.0.0.255 area 1

[hhhax7]

So maybe I messed up. I see that you put on R3 "area 1 virtual-link 1.1.1.1". Is that correct? I thought you needed to put the IP of the next hop you are using to get to the backbone area. So wouldn't the command on R3 be " area 1 virtual link 2.2.2.2"? And from my understanding, it needs to be on the opposite side as well, so wouldn't R2 need "area 1 virtual like 3.3.3.3"? Or am I wrong?

[Georg Pauwen]

Hello,

test the configs I posted, it should work.

The link below has a pretty good sample configuration:

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

[hhhax7]

Don't mean to be rude but the config you posted is incorrect. 

[Georg Pauwen]

Hello,

which config is incorrect, and what is incorrect ?

[hhhax7]

The virtual link config. Needs to be configured on R2 and R3

R2
area 1 virtual-link 3.3.3.3

R3
area 1 virtual-link 2.2.2.2

[Georg Pauwen]

Hello,

which config are you referring to ? In the one I posted, R1 and R3 are the ABRs. VL is between ABRs...

[hhhax7]

R2 and R3 are the ABRs in my topology. R1 is the backbone router

[Georg Pauwen]

Hello,

post the full running configs of all your three routers. My configs are just an example. As initially stated, I could not tell from your drawing what areas you networks belong to.

[paul driver]

Hello

---

@hhhax7 wrote:

So maybe I messed up. I see that you put on R3 "area 1 virtual-link 1.1.1.1". Is that correct? I thought you needed to put the IP of the next hop you are using to get to the backbone area. So wouldn't the command on R3 be " area 1 virtual link 2.2.2.2"? And from my understanding, it needs to be on the opposite side as well, so wouldn't R2 need "area 1 virtual like 3.3.3.3"? Or am I wrong?

---

Your correct the VL needs to be configured between ABR's -  in your toplogy that would be R2 (area 0-1), R3 (area1-10)
R2
area 1 virtual-link 3.3.3.3

R3
area 1 virtual-link 2.2.2.2

As to the reason why it didnt work , Did you clear the opsf process after you had deleted the previous VL?

[hhhax7]

I did not clear it. But what is weird is I deleted the original VL, the new one still didnt work (showed as down), so I put the original one back on and it came up. 

[paul driver]

Hello

It would hard to say now what could have been the issue, However I would just to confirm that your original query reagrds the VL configuration relating to your topology was indeed correct.

[hhhax7]

So I have been researching and have not found a solid answer. What would you do if you has a VL showing as down? In all my studies so far for the ROUTE, I have no come across anything about it yet. This include the OCG, a class through Global Knowledge, a course on Udemy by Chris Bryant, Chris Bryant's study guide, as well as cisco docs.