Solved: OSPF NSSA and Totally NSSA Area LSA 7 Issue

libra_ali786 · ‎12-05-2021

I have a test environment. I have 4 ospf areas "Area 0 backbone , Area 1 normal , Area 2 NSSA and Area 3 Totally NSSA." Inside the Area 2 I redistributed EIGRP 20 and Area 3 i redistributed RIP. I have one more network EIGRP-1

which is connected with backbone Area OSPF 0 and redistributed in OSPF 0.

When I look my Routers - R5 (Area 2 NSSA) and R6 (Area 3 Totally NSSA) , I can see the EIGRP-1 routes in there table (10.10.10.0 , 20.20.20.0 , 192.168.1.0 and 192.168.2.0) and there OSPF database showing EIGRP-1 routes as a LSA 7.

1- Why I am getting EIGRP-1 routes inside R5 and R6 as a LSA-7 ?

2- If my backbone Area 0 Router R3 push the LSA-7 routes to R5 and R6 then why it is not exchanging to R5 (EIGRP-2) and R6 (RIP) external routes respectively?

3- As per my knowledge ABR convert the LSA 7 into LSA 5 , but when i see my R3 , R5 and R6 routers EIGRP -1 routes showing as a LSA-7.

Please explain this behaviors of R5 and R6.

I attached images R3 , R5 and R6 Routing table and Database information which is pointing the EIGRP-1 Routes as LSA 7.

Richard Burts · ‎12-06-2021

Thanks for the additional information. I believe that I understand better what is going on and suggest these as answers to your questions:

1- Why I am getting EIGRP-1 routes inside R5 and R6 as a LSA-7 ?

R5 and R6 are running a single dynamic routing protocol OSPF and you are seeing in their tables what they learned from R3. So we should focus our attention on R3 which is advertising the routes as LSA 7.

R3 is running EIGRP and learning routes from R2. And R3 redistributes the EIGRP routes that it learned from R2. As you are aware in normal OSPF a redistributed route would have LSA 5. But for NSSA the redistributed route is LSA 7. So R3 redistributes the EIGRP routes and advertises them to R5 and R6 as LSA 7.

2- You as asking why does R3 advertise some LSA 7 and not advertise other LSA 7. The key to understanding this is to look at where the redistribution is being done. Redistribution of EIGRP 1 is done on R3 and R3 advertises the LSA 7 to its neighbors. Redistribution of EIGRP 2 and of RIP is being done on R4 and R7. R3 learns those routes as LSA 7. And one of the most important aspects of being NSSA is that you do not learn External routes learned in different areas. Externals from area 2 can not be advertised into area 3 and Externals from area 3 can not be advertised into area 2.

3- As per my knowledge ABR convert the LSA 7 into LSA 5 , but when i see my R3 , R5 and R6 routers EIGRP -1 routes showing as a LSA-7. This is a more subtle issue than the other 2. The key thing to understand here is that the ABR does translate LSA 7 into LSA 5, but it does this only when advertising into area 0. If you had another router that was running OSPF and connected in area 0 then its table would have EIGRP 1 routes as LSA 5. But R3 as ABR redistributes EIGRP 1 routes and advertises them into areas 2 and 3 as LSA 7.

HTH

Rick

View solution in original post

Georg Pauwen · ‎12-05-2021

Hello,

this one is going to be difficult to answer without seeing the full configs of all routers, can you post these ?

libra_ali786 · ‎12-05-2021

Please look my All routers Configurations:

R1#show run

 
!
interface Loopback1
ip address 192.168.1.1 255.255.255.0
!
interface Loopback2
ip address 192.168.2.1 255.255.255.0
!
interface FastEthernet0/0
ip address 10.10.10.2 255.255.255.0
duplex auto
speed auto
!
!
router eigrp 1
network 10.10.10.0 0.0.0.255
network 192.168.1.0
network 192.168.2.0
!

R2#show run

 !
interface FastEthernet0/0
ip address 10.10.10.1 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet0/1
ip address 20.20.20.1 255.255.255.0
duplex auto
speed auto
!
!
router eigrp 1
network 10.10.10.0 0.0.0.255
network 20.20.20.0 0.0.0.255
!







R3#show run

version 15.2

interface Loopback1

 ip address 200.200.200.2 255.255.255.0

 ip ospf network point-to-point

!        

interface FastEthernet0/0

 ip address 50.50.50.2 255.255.255.0

 duplex auto

 speed auto

!        

interface FastEthernet0/1

 ip address 20.20.20.2 255.255.255.0

 duplex auto

 speed auto

!        

interface FastEthernet1/0

 ip address 80.80.80.2 255.255.255.0

 duplex auto

 speed auto

!        

interface FastEthernet1/1

 ip address 60.60.60.2 255.255.255.0

 duplex auto

 speed auto

!        

router eigrp 1

 network 20.20.20.0 0.0.0.255

 redistribute ospf 1 metric 1 1 1 1 1

!        

router ospf 1

 router-id 3.3.3.3

 area 2 nssa default-information-originate

 area 3 nssa no-summary

 redistribute eigrp 1 subnets

 network 50.50.50.0 0.0.0.255 area 2

 network 60.60.60.0 0.0.0.255 area 3

 network 80.80.80.0 0.0.0.255 area 1

 network 200.200.200.0 0.0.0.255 area 0

!         

 R5#show run

!
interface FastEthernet0/0
ip address 50.50.50.1 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet0/1
ip address 40.40.40.1 255.255.255.0
duplex auto
speed auto

!
router ospf 1
router-id 5.5.5.5
area 2 nssa
network 40.40.40.0 0.0.0.255 area 2
network 50.50.50.0 0.0.0.255 area 2
!




R4#show run

!
interface Loopback1
ip address 44.44.44.1 255.255.255.0
ip ospf network point-to-point
!
interface FastEthernet0/0
ip address 111.111.110.2 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet0/1
ip address 40.40.40.2 255.255.255.0
duplex auto
speed auto
!
!
router eigrp 20
network 111.111.110.0 0.0.0.255
redistribute ospf 1 metric 1 1 1 1 1
!
router ospf 1
router-id 4.4.4.4
area 2 nssa
redistribute eigrp 20 subnets
network 40.40.40.0 0.0.0.255 area 2
network 44.44.44.0 0.0.0.255 area 2
!

 R11#show run

!
!
interface Loopback1
ip address 111.111.111.1 255.255.255.0
ip ospf network point-to-point
!
interface Loopback2
ip address 111.111.112.1 255.255.255.0
!
interface FastEthernet0/0
ip address 111.111.110.1 255.255.255.0
duplex auto
speed auto
!
!
router eigrp 20
network 111.111.110.0 0.0.0.255
network 111.111.111.0 0.0.0.255
network 111.111.112.0 0.0.0.255
!
router ospf 1
area 3 stub
network 70.70.70.0 0.0.0.255 area 3
network 77.77.77.0 0.0.0.255 area 3
!

 R6#show run

 !
interface FastEthernet0/0
ip address 70.70.70.1 255.255.255.0
duplex auto
speed auto
!
 
interface FastEthernet1/1
ip address 60.60.60.1 255.255.255.0
duplex auto
speed auto
!
!
router ospf 1
router-id 6.6.6.6
area 3 nssa
network 60.60.60.0 0.0.0.255 area 3
network 70.70.70.0 0.0.0.255 area 3
!







R7#show run

!
!
interface Loopback1
ip address 77.77.77.1 255.255.255.0
ip ospf network point-to-point
!
interface FastEthernet0/0
ip address 70.70.70.2 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet0/1
ip address 100.100.100.2 255.255.255.0
duplex auto
speed auto
!
!
router ospf 1
area 3 nssa
redistribute rip subnets
network 70.70.70.0 0.0.0.255 area 3
network 77.77.77.0 0.0.0.255 area 3
!
router rip
version 2
redistribute ospf 1 metric 10
network 100.0.0.0
no auto-summary
!

 R10#show run

!
!
interface Loopback1
ip address 100.100.110.1 255.255.255.0
ip ospf network point-to-point
!
interface Loopback2
ip address 100.100.120.1 255.255.255.0
!
interface FastEthernet0/0
ip address 70.70.70.2 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet0/1
ip address 100.100.100.1 255.255.255.0
duplex auto
speed auto
!
!
router ospf 1
area 3 stub
network 70.70.70.0 0.0.0.255 area 3
network 77.77.77.0 0.0.0.255 area 3
!
router rip
version 2
network 100.0.0.0
no auto-summary
!

 R8#show run

!
!
interface FastEthernet0/0
ip address 90.90.90.1 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet1/0
ip address 80.80.80.1 255.255.255.0
duplex auto
speed auto
!
!
router ospf 1
router-id 8.8.8.8
network 80.80.80.0 0.0.0.255 area 1
network 90.90.90.0 0.0.0.255 area 1
!










R9#show run

!
!
interface Loopback1
ip address 99.99.99.1 255.255.255.0
ip ospf network point-to-point
!
interface FastEthernet0/0
ip address 90.90.90.2 255.255.255.0
duplex auto
speed auto
!
!
router ospf 1
network 90.90.90.0 0.0.0.255 area 1
network 99.99.99.0 0.0.0.255 area 1
!

Richard Burts · ‎12-06-2021

While I work through the logic here I will start with 2 questions:

- can you provide a simple diagram which shows the topology and relationships?

- is this implemented on real hardware or is this in a simulator? If so, which simulator?

HTH

Rick

libra_ali786 · ‎12-06-2021

Thanks for the reply.

---   I attached the topology with relationship.

--- I used the GNS-3  emulator 7200 Router series.

Richard Burts · ‎12-06-2021

Thanks for the additional information. I believe that I understand better what is going on and suggest these as answers to your questions:

1- Why I am getting EIGRP-1 routes inside R5 and R6 as a LSA-7 ?

R5 and R6 are running a single dynamic routing protocol OSPF and you are seeing in their tables what they learned from R3. So we should focus our attention on R3 which is advertising the routes as LSA 7.

R3 is running EIGRP and learning routes from R2. And R3 redistributes the EIGRP routes that it learned from R2. As you are aware in normal OSPF a redistributed route would have LSA 5. But for NSSA the redistributed route is LSA 7. So R3 redistributes the EIGRP routes and advertises them to R5 and R6 as LSA 7.

2- You as asking why does R3 advertise some LSA 7 and not advertise other LSA 7. The key to understanding this is to look at where the redistribution is being done. Redistribution of EIGRP 1 is done on R3 and R3 advertises the LSA 7 to its neighbors. Redistribution of EIGRP 2 and of RIP is being done on R4 and R7. R3 learns those routes as LSA 7. And one of the most important aspects of being NSSA is that you do not learn External routes learned in different areas. Externals from area 2 can not be advertised into area 3 and Externals from area 3 can not be advertised into area 2.

3- As per my knowledge ABR convert the LSA 7 into LSA 5 , but when i see my R3 , R5 and R6 routers EIGRP -1 routes showing as a LSA-7. This is a more subtle issue than the other 2. The key thing to understand here is that the ABR does translate LSA 7 into LSA 5, but it does this only when advertising into area 0. If you had another router that was running OSPF and connected in area 0 then its table would have EIGRP 1 routes as LSA 5. But R3 as ABR redistributes EIGRP 1 routes and advertises them into areas 2 and 3 as LSA 7.

HTH

Rick

libra_ali786 · ‎12-06-2021

Thanks You very much for the detail answered. It is clear all my doubts.

Richard Burts · ‎12-06-2021

You are welcome. I am glad that my explanation was helpful. Thank you for marking this question as solved. This will help other participants in the community to identify discussions which have helpful information. This community is an excellent place to ask questions and to learn about networking. I hope to see you continue to be active in the community.

HTH

Rick

MHM Cisco World · ‎12-05-2021

Area NSSA & T-NSSA
the condition to make the Area as NSSA & T-NSSA is
have one ASBR which redistribute other OSPF process or EIGRP or BGP
have one ABR which connect NSSA area to backbone area.

so add R between R3 R6
and R between R3 R5.

MHM Cisco World · ‎12-06-2021

may be my last answer not clarify so much but in simple word,
R3 represent the ASBR for Area 0,1,2,3
and also in same time it represent ABR for Area 0,1,2,3.

as I mention before ASBR for Area 0 will redistribute EIGRP as LSA 5
BUUUUTTTT
OSPF for NSSA and T-NSSA will redistribute EIGRP as LSA 7.
so how we can solve this.

we can make NSSA not redistribute the EIGRP into NSSA & T-NSSA by
area nssa no-redistrubte

or add other routerS to be separate the ASBR from ABR. "new routerS will be ABR for Area1,2,3".

MHM Cisco World · ‎12-11-2021

libra_ali786 · ‎12-12-2021

Thanks for the showing another way to block the LSA 7 into NSSA Area .