Need help with OSPF lab

[Lokhilesh Takoor]

Hello,

I was wondering if you could help me :

I was doing the lab 3-2 on this pdf : http://www.kis.fri.uniza.sk/~palo/Netacad/LST/ccnp-route-v6/en_ROUTE_SLM_v6000.pdf

I used this configuration the the three routers :

Router R1
hostname R1
!
interface Loopback1
description Engineering Department
ip address 10.1.1.1 255.255.255.0
ip ospf network point-to-point
!
interface Serial0/0/0
ip address 10.1.12.1 255.255.255.0
clock rate 64000
no shutdown
!
router ospf 1
network 10.1.1.0 0.0.0.255 area 0
network 10.1.12.0 0.0.0.255 area 0
!
end
===============================================================================
Router R2
hostname R2
!
interface Loopback2
description Marketing Department
ip address 10.1.2.1 255.255.255.0
ip ospf network point-to-point
!
interface Serial0/0/0
ip address 10.1.12.2 255.255.255.0
no shutdown
!
interface Serial0/0/1
ip address 10.1.23.2 255.255.255.0
clock rate 64000
no shutdown
!
router ospf 1
network 10.1.2.0 0.0.0.255 area 0
network 10.1.12.0 0.0.0.255 area 0
network 10.1.23.0 0.0.0.255 area 23
!
end


======================================================================
Router R3
hostname R3
!
All contents are Copyright © 1992–2010 Cisco Systems, Inc. All rights reserved. This document is Cisco Public Information.
Page 17 of 18CCNPv6 ROUTE
interface Loopback3
description Accounting Department
ip address 10.1.3.1 255.255.255.0
ip ospf network point-to-point
!
interface Loopback20
description Connection to another AS
ip address 172.20.200.1 255.255.255.0
!
interface Serial0/0/1
ip address 10.1.23.3 255.255.255.0
no shutdown
!
router ospf 1
network 10.1.3.0 0.0.0.255 area 23
network 10.1.23.0 0.0.0.255 area 23
!
end

However unlike on the lab when I do a : show ip ospf neighbors

I get 172.20.200.1 as neighbor and not 10.1.3.1 as it mentions on the lab on page 155 ( same lab ). Can someone help explain? I am not advertising that network (172....) why is it showing up as neighbor?

I am using 3500 router image on GNS3.

thanks

[Mark Malone · Accepted solution]

Hey Its because you have redistributed connected subnets on r3 which automatically advertised any connected interface into ospf , advertises the 172 network and because that's the highest logical ip address it is chosen as the neighbour and router id instead of 10.1.3.1 :)

[Lokhilesh Takoor]

Hello ,

thanks for the reply. Actually I need to remove that "redistribute connected subnets". I did not do any redistribution. I can however understand that 172 is the highest logical IP, but even when I used : ip ospf network point-to-point under Loopback 3 it still advertises 172 instead of 10.1.3.1??

[Mark Malone · Accepted solution]

Hey yes but after the command was entered into the process did you clear the LSDB to reset the elections and neighbours , once the redistribute command is gone through even after removing it you would need to clear the ospf LSDB clear process command in global config

can you clear the process and post the ospf config and the show ip route for r3 and we can see if anything else is causing it

[Lokhilesh Takoor]

Hello Rolf and Mark,

Thank you very much for your help on this lab it seems there are a few errors in it that made me confused. I did do a clear process however and even lowered the hello and dead timer. But it was not changing, then I had to switch off the router (this is on gns3 using 3400 router image so I am assuming this is a bug).

After I removed the redistribute command and also the interface i restarted it and voila, it took up Loopback interface 3 as neighbor. I added the RID as 10.1.3.1 and it works now.

[Mark Malone]

ah great glad you got it sorted yes definitely some of those gns3 images are old an bit buggy , I would try use the 7200 device when on gns3 there are still images being released last year for that platform that can be uploaded into gns3 least that way your not battling old software problems too

[Rolf Fischer · Accepted solution]

Hi,

if you don't specifiy an OSPF RID with the 'router-id' command under the OSPF process, next step in the election process is to find the active loopback interface with the highest IP address. In the election process it makes no difference weather this loopback address is advertised as a prefix in the LSDB or not. Note that the OSPF RID is not an IP address, it is just an 32-bit identifier. You can even assign RIDs like 0.0.0.1, 224.0.0.0 or 255.255.255.255 if you want to.

Once the OSPF RID is elected, there is no preemption in case of activating a new loopback interface with a higher IP address, because this would cause undesirable instabilities. As Mark has already said, you'd need to clear the process for a re-election. So we can assume that in the PDF example loopback 20 was activated after the initial local RID election had taken place already.

HTH
Rolf