NSSA AREA OSPF ISSUE

[Ammartehsein]

I am having issue, I have attached my topology diagram. R2 and R4 are ABRs, R5 is ASBR. Area is nssa. The issue is that on R4 I am receiving route Like expected as N2, But on R2 I received route as External routes E2.

R2=======

6.0.0.0/32 is subnetted, 1 subnets
O E2 6.6.6.6 [110/10] via 192.168.2.5, 00:00:13, Serial1/0
172.16.0.0/24 is subnetted, 3 subnets
O E2 172.16.12.0 [110/10] via 192.168.2.5, 00:00:13, Serial1/0
O E2 172.16.10.0 [110/10] via 192.168.2.5, 00:00:13, Serial1/0
O E2 172.16.11.0 [110/10] via 192.168.2.5, 00:00:13, Serial1/0
7.0.0.0/32 is subnetted, 1 subnets
O IA 7.7.7.7 [110/66] via 20.20.20.3, 00:00:28, FastEthernet0/0
8.0.0.0/32 is subnetted, 1 subnets
O 8.8.8.8 [110/67] via 20.20.20.3, 00:06:07, FastEthernet0/0
9.0.0.0/32 is subnetted, 1 subnets
O IA 9.9.9.9 [110/3] via 20.20.20.3, 00:06:07, FastEthernet0/0
O IA 192.168.5.0/24 [110/66] via 20.20.20.3, 00:00:28, FastEthernet0/0
10.0.0.0/32 is subnetted, 1 subnets
O IA 10.10.10.10 [110/3] via 20.20.20.3, 00:06:07, FastEthernet0/0
O IA 192.168.6.0/24 [110/65] via 20.20.20.3, 00:06:07, FastEthernet0/0
O 192.168.1.0/24 [110/128] via 192.168.2.5, 00:00:28, Serial1/0
C 192.168.2.0/24 is directly connected, Serial1/0
192.168.3.0/32 is subnetted, 3 subnets
O IA 192.168.3.10 [110/2] via 20.20.20.3, 00:06:07, FastEthernet0/0
O IA 192.168.3.9 [110/2] via 20.20.20.3, 00:06:07, FastEthernet0/0
O IA 192.168.3.3 [110/1] via 20.20.20.3, 00:06:07, FastEthernet0/0
O*E2 0.0.0.0/0 [110/1] via 20.20.20.1, 00:06:07, FastEthernet0/0
R2#sh ip route 172.16.12.0
Routing entry for 172.16.12.0/24
Known via "ospf 1", distance 110, metric 10, type extern 2, forward metric 65
Last update from 192.168.2.5 on Serial1/0, 00:00:19 ago
Routing Descriptor Blocks:
* 192.168.2.5, from 4.4.4.4, 00:00:19 ago, via Serial1/0
Route metric is 10, traffic share count is 1

R4=====

2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/2] via 20.20.20.2, 00:13:07, FastEthernet0/0
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/2] via 20.20.20.3, 00:13:07, FastEthernet0/0
4.0.0.0/32 is subnetted, 1 subnets
C 4.4.4.4 is directly connected, Loopback1
20.0.0.0/24 is subnetted, 2 subnets
C 20.20.20.0 is directly connected, FastEthernet0/0
O 20.20.30.0 [110/66] via 20.20.20.3, 00:13:08, FastEthernet0/0
5.0.0.0/32 is subnetted, 1 subnets
O 5.5.5.5 [110/65] via 192.168.1.5, 00:12:52, Serial1/1
6.0.0.0/32 is subnetted, 1 subnets
O N2 6.6.6.6 [110/10] via 192.168.1.5, 00:12:53, Serial1/1
172.16.0.0/24 is subnetted, 3 subnets
O N2 172.16.12.0 [110/10] via 192.168.1.5, 00:12:53, Serial1/1
O N2 172.16.10.0 [110/10] via 192.168.1.5, 00:12:53, Serial1/1
O N2 172.16.11.0 [110/10] via 192.168.1.5, 00:12:53, Serial1/1
7.0.0.0/32 is subnetted, 1 subnets
O IA 7.7.7.7 [110/66] via 20.20.20.3, 00:12:53, FastEthernet0/0
8.0.0.0/32 is subnetted, 1 subnets
O 8.8.8.8 [110/67] via 20.20.20.3, 00:13:08, FastEthernet0/0
9.0.0.0/32 is subnetted, 1 subnets
O IA 9.9.9.9 [110/3] via 20.20.20.3, 00:13:08, FastEthernet0/0
O IA 192.168.5.0/24 [110/66] via 20.20.20.3, 00:12:53, FastEthernet0/0
10.0.0.0/32 is subnetted, 1 subnets
O IA 10.10.10.10 [110/3] via 20.20.20.3, 00:13:08, FastEthernet0/0
O IA 192.168.6.0/24 [110/65] via 20.20.20.3, 00:13:08, FastEthernet0/0
C 192.168.1.0/24 is directly connected, Serial1/1
O 192.168.2.0/24 [110/128] via 192.168.1.5, 00:12:53, Serial1/1
192.168.3.0/32 is subnetted, 3 subnets
O IA 192.168.3.10 [110/2] via 20.20.20.3, 00:13:08, FastEthernet0/0
O IA 192.168.3.9 [110/2] via 20.20.20.3, 00:13:08, FastEthernet0/0
O IA 192.168.3.3 [110/1] via 20.20.20.3, 00:13:08, FastEthernet0/0
O*E2 0.0.0.0/0 [110/1] via 20.20.20.1, 00:13:08, FastEthernet0/0

R5======

Gateway of last resort is not set

1.0.0.0/32 is subnetted, 1 subnets
O IA 1.1.1.1 [110/66] via 192.168.2.2, 00:14:20, Serial1/0
[110/66] via 192.168.1.4, 00:13:21, Serial1/1
2.0.0.0/32 is subnetted, 1 subnets
O IA 2.2.2.2 [110/65] via 192.168.2.2, 00:14:20, Serial1/0
3.0.0.0/32 is subnetted, 1 subnets
O IA 3.3.3.3 [110/66] via 192.168.2.2, 00:14:20, Serial1/0
[110/66] via 192.168.1.4, 00:13:21, Serial1/1
4.0.0.0/32 is subnetted, 1 subnets
O IA 4.4.4.4 [110/65] via 192.168.1.4, 00:13:21, Serial1/1
20.0.0.0/24 is subnetted, 2 subnets
O IA 20.20.20.0 [110/65] via 192.168.2.2, 00:14:20, Serial1/0
[110/65] via 192.168.1.4, 00:13:21, Serial1/1
O IA 20.20.30.0 [110/130] via 192.168.2.2, 00:14:21, Serial1/0
[110/130] via 192.168.1.4, 00:13:21, Serial1/1
5.0.0.0/32 is subnetted, 1 subnets
C 5.5.5.5 is directly connected, Loopback0
6.0.0.0/32 is subnetted, 1 subnets
D 6.6.6.6 [90/156160] via 192.168.20.6, 02:19:44, FastEthernet0/0
172.16.0.0/24 is subnetted, 3 subnets
D 172.16.12.0 [90/156160] via 192.168.20.6, 02:19:55, FastEthernet0/0
D 172.16.10.0 [90/156160] via 192.168.20.6, 02:20:02, FastEthernet0/0
D 172.16.11.0 [90/156160] via 192.168.20.6, 02:19:59, FastEthernet0/0
7.0.0.0/32 is subnetted, 1 subnets
O IA 7.7.7.7 [110/130] via 192.168.2.2, 00:14:21, Serial1/0
[110/130] via 192.168.1.4, 00:13:21, Serial1/1
8.0.0.0/32 is subnetted, 1 subnets
O IA 8.8.8.8 [110/131] via 192.168.2.2, 00:14:21, Serial1/0
[110/131] via 192.168.1.4, 00:13:21, Serial1/1
9.0.0.0/32 is subnetted, 1 subnets
O IA 9.9.9.9 [110/67] via 192.168.2.2, 00:14:21, Serial1/0
[110/67] via 192.168.1.4, 00:13:21, Serial1/1
C 192.168.20.0/24 is directly connected, FastEthernet0/0
O IA 192.168.5.0/24 [110/130] via 192.168.2.2, 00:14:21, Serial1/0
[110/130] via 192.168.1.4, 00:13:21, Serial1/1
10.0.0.0/32 is subnetted, 1 subnets
O IA 10.10.10.10 [110/67] via 192.168.2.2, 00:14:21, Serial1/0
[110/67] via 192.168.1.4, 00:13:21, Serial1/1
O IA 192.168.6.0/24 [110/129] via 192.168.2.2, 00:14:21, Serial1/0
[110/129] via 192.168.1.4, 00:13:21, Serial1/1
C 192.168.1.0/24 is directly connected, Serial1/1
C 192.168.2.0/24 is directly connected, Serial1/0
192.168.3.0/32 is subnetted, 3 subnets
O IA 192.168.3.10 [110/66] via 192.168.2.2, 00:14:21, Serial1/0
[110/66] via 192.168.1.4, 00:13:21, Serial1/1
O IA 192.168.3.9 [110/66] via 192.168.2.2, 00:14:21, Serial1/0
[110/66] via 192.168.1.4, 00:13:21, Serial1/1
O IA 192.168.3.3 [110/65] via 192.168.2.2, 00:14:21, Serial1/0
[110/65] via 192.168.1.4, 00:13:21, Serial1/1

[MHM Cisco World]

in R5 can I see 

show ip protocol <<-

MHM

[Ammartehsein]

R5#sh ip pro
R5#sh ip protocols
Routing Protocol is "ospf 1"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Router ID 5.5.5.5
It is an autonomous system boundary router
Redistributing External Routes from,
connected
static, includes subnets in redistribution
eigrp 1 with metric mapped to 10, includes subnets in redistribution
Number of areas in this router is 1. 0 normal 0 stub 1 nssa
Maximum path: 4
Routing for Networks:
Routing on Interfaces Configured Explicitly (Area 51):
Loopback0
Serial1/1
Serial1/0
Reference bandwidth unit is 100 mbps
Passive Interface(s):
FastEthernet0/0
Routing Information Sources:
Gateway Distance Last Update
2.2.2.2 110 01:01:50
4.4.4.4 110 01:00:50
Distance: (default is 110)

Routing Protocol is "eigrp 1"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
EIGRP maximum hopcount 100
EIGRP maximum metric variance 1
Redistributing: ospf 1, eigrp 1
EIGRP NSF-aware route hold timer is 240s
Automatic network summarization is not in effect
Maximum path: 4
Routing for Networks:
192.168.20.0
Routing Information Sources:
Gateway Distance Last Update
192.168.20.6 90 03:07:13
Distance: internal 90 external 170

R5# sh ip os
R5# sh ip ospf
Routing Process "ospf 1" with ID 5.5.5.5
Start time: 00:00:25.836, Time elapsed: 03:33:44.684
Supports only single TOS(TOS0) routes
Supports opaque LSA
Supports Link-local Signaling (LLS)
Supports area transit capability
It is an autonomous system boundary router
Redistributing External Routes from,
connected
static, includes subnets in redistribution
eigrp 1 with metric mapped to 10, includes subnets in redistribution
Router is not originating router-LSAs with maximum metric
Initial SPF schedule delay 5000 msecs
Minimum hold time between two consecutive SPFs 10000 msecs
Maximum wait time between two consecutive SPFs 10000 msecs
Incremental-SPF disabled
Minimum LSA interval 5 secs
Minimum LSA arrival 1000 msecs
LSA group pacing timer 240 secs
Interface flood pacing timer 33 msecs
Retransmission pacing timer 66 msecs
Number of external LSA 0. Checksum Sum 0x000000
Number of opaque AS LSA 0. Checksum Sum 0x000000
Number of DCbitless external and opaque AS LSA 0
Number of DoNotAge external and opaque AS LSA 0
Number of areas in this router is 1. 0 normal 0 stub 1 nssa
Number of areas transit capable is 0
External flood list length 0
IETF NSF helper support enabled
Cisco NSF helper support enabled
Area 51
Number of interfaces in this area is 3 (1 loopback)
It is a NSSA area
Area has no authentication
SPF algorithm last executed 01:00:59.636 ago
SPF algorithm executed 3 times
Area ranges are
Number of LSA 37. Checksum Sum 0x1E41C9
Number of opaque link LSA 0. Checksum Sum 0x000000
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0

R5#

[MHM Cisco World]

Number of areas in this router is 1. 0 normal 0 stub 1 nssa <<- in R5 there is only one area which is nssa that correct.

In R2 and R4 check config it can mismatch area config.

MHM

[Ammartehsein]

R2====

R2#sh run
Building configuration...

Current configuration : 1559 bytes
!
upgrade fpd auto
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R2
!
boot-start-marker
boot-end-marker
!
logging message-counter syslog
!
no aaa new-model
ip source-route
no ip icmp rate-limit unreachable
ip cef
!
!
!
!
no ip domain lookup
no ipv6 cef
!
multilink bundle-name authenticated
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
archive
log config
hidekeys
!
!
!
!
!
ip tcp synwait-time 5
!
!
!
!
interface Loopback1
ip address 2.2.2.2 255.255.255.255
ip ospf 1 area 0
!
interface FastEthernet0/0
ip address 20.20.20.2 255.255.255.0
ip ospf 1 area 0
duplex half
!
interface Serial1/0
ip address 192.168.2.2 255.255.255.0
ip ospf authentication
ip ospf authentication-key 123
ip ospf 1 area 51
serial restart-delay 0
!
interface Serial1/1
no ip address
ip ospf 1 area 51
shutdown
serial restart-delay 0
!
interface Serial1/2
no ip address
shutdown
serial restart-delay 0
!
interface Serial1/3
no ip address
shutdown
serial restart-delay 0
!
interface FastEthernet2/0
no ip address
shutdown
duplex half
!
router ospf 1
router-id 2.2.2.2
log-adjacency-changes
area 0 authentication
area 51 nssa
!
ip forward-protocol nd
no ip http server
no ip http secure-server
!
!
!
no cdp log mismatch duplex
!
!
!
!
!
!
control-plane
!
!
!
!
!
!
!
gatekeeper
shutdown
!
!
line con 0
exec-timeout 0 0
privilege level 15
logging synchronous
stopbits 1
line aux 0
exec-timeout 0 0
privilege level 15
logging synchronous
stopbits 1
line vty 0 4
login
!
end

R4====

!
hostname R4
!
boot-start-marker
boot-end-marker
!
logging message-counter syslog
!
no aaa new-model
ip source-route
no ip icmp rate-limit unreachable
ip cef
!
!
!
!
no ip domain lookup
no ipv6 cef
!
multilink bundle-name authenticated
!
!
key chain myKeyMD5
key 1
key-string test
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
archive
log config
hidekeys
!
!
!
!
!
ip tcp synwait-time 5
!
!
!
!
interface Loopback1
ip address 4.4.4.4 255.255.255.255
ip ospf 1 area 0
!
interface FastEthernet0/0
ip address 20.20.20.4 255.255.255.0
ip ospf 1 area 0
duplex half
!
interface Serial1/0
no ip address
shutdown
serial restart-delay 0
!
interface Serial1/1
ip address 192.168.1.4 255.255.255.0
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 456
ip ospf 1 area 51
serial restart-delay 0
!
interface Serial1/2
no ip address
shutdown
serial restart-delay 0
!
interface Serial1/3
no ip address
shutdown
serial restart-delay 0
!
interface FastEthernet2/0
no ip address
ip ospf authentication message-digest
ip ospf authentication-key test1
ip ospf message-digest-key 1 md5 cisco
ip ospf 1 area 51
shutdown
duplex half
!
router ospf 1
router-id 4.4.4.4
log-adjacency-changes
area 0 authentication
area 51 nssa
!
ip forward-protocol nd
ip route 4.4.4.4 255.255.255.255 Loopback1
no ip http server
no ip http secure-server
!
!
!
no cdp log mismatch duplex
!
!
!
!
!
!
control-plane
!
!
!
!
!
!
!
gatekeeper
shutdown
!
!
line con 0
exec-timeout 0 0
privilege level 15
logging synchronous
stopbits 1
line aux 0
exec-timeout 0 0
privilege level 15
logging synchronous
stopbits 1
line vty 0 4
login
!
end

[Ammartehsein]

I pasted router 2 and router config above, The issue is that Router 4 is advertising exertanal lsa, which router2 adds in routing table.

[MHM Cisco World]

Yes friend I know that same prefix appear in one router as O N1/2 and in other O E1/2

So config is correct but you use ospf under interface' I see issue before about order of commands' try clear ospf process in R2/R4/R5 and check.

MHM

[Ammartehsein]

I did clear osf process multiple times

[MHM Cisco World]

I run lab there is no such as this behave 
if you can share 
show ip ospf interface brief in R2/4/5
show ip route < > in R2/4
show ip ospf database self in R5

let see why R5 send prefix as E not as N

MHM

[Joseph W. Doherty]

Not necessarily related to your question, but from you topology diagram, it appears area zero is partitioned, correct?

[Giuseppe Larosa · Accepted solution]

Hello @Ammartehsein ,

what you see may be normal because:

if there are two ABR nodes serving area0 and NSSA area 51   LSA type 7 are converted to LSA type 5 only by the ABR with lowest RID R2. The other ABR between area 0 and area 51  R4 (0,51) prefers to install the LSA type 5 O E2 routes originated by R2 over the O N2 generated by R5.

R5 can decide what prefixes are to be translated using the P bit P=propagate.

The reason is that only one ABR makes the translation between LSA type 7 and LSA type 5 , the other one suppresses its own translations.

use

show ip ospf 1 database

or isolate R2 from area 51 and you will see R4 starting to generate O E2 = LSA type 5 and R4 routing table will show the O N2 coming from R5.

Hope to help

Giuseppe

[MHM Cisco World]

@Giuseppe Larosa are you sure about this statement?

It translate lsa not change type. 

O E must come from router do redistrubte.

MHM

[Giuseppe Larosa]

Hello @MHM Cisco World ,

when lsa type is changed the code changes from O N2 to O E2 in the routing table I'm sure about this. Remember that the IP routing is NO§T the ospf database and it is managed by the IP routing daemon.

OSPF is link state and when NSSA areas have been introduced the guys who have written the RFC had the usual idea to minimize the number of external routes this is why the second ABR suppresses its own conversion.

there is a blog from deepak Aurora that shows this.

I have done tests on this too. You have a lab test it.

Edit:

here is the link

https://anetworkartist.blogspot.com/search?q=NSSA

Hope to help

Giuseppe

[MHM Cisco World]

I dont think this is case here' I run lab and I see O N in both ABR (interconnect by link as OP use).

Again O E is generate only by ASBR' so R2 if run one ospf process then it only ABR and can not change type of ospf prefix' 

Note:- I am talking about prefix type not lsa type.

MHM

[Giuseppe Larosa]

Hello @MHM Cisco World ,

I'm busy with work however you agree with me that only one ABR will make the translation to area 0.0.0.0 ?

Best Regards

Giuseppe