Why did the Summary Null Route disappear from the ABR's Routing Table

[jwangCisco]

Hi Experts, 

Just testing out the simple theory...

I could not figure out why a route was missing from the ABR's routing table :

Could anybody please shed light for me:

I understood the theory that said : [ when you place the

Area Range

command on the ABR, then a Summary route to null0 was supposed to be installed into this ABR’s routing table ].

It did not happen on my ABR router.

I had labbed it up using Packet Tracer , with the following configurations, and a Summary Null route is currently missing from Router B’s table :

Please see my simple topology diagram :
Router B is the NSSA ABR , and is connecting to two areas : the backbone internal Router A, as well as connecting to Area 1 NSSA Router C (NSSA ASBR) .

**** Below is the configuration for NSSA ABR (Router B)

hostname Router

no ip cef

no ipv6 cef

spanning-tree mode pvst




interface FastEthernet0/0

 ip address 10.1.2.2 255.255.255.0




interface FastEthernet0/1

 ip address 1.1.1.1 255.255.255.0




router ospf 24

 log-adjacency-changes

 area 0 range 10.0.0.0 255.0.0.0

 area 1 nssa

 network 10.0.0.0 0.255.255.255 area 0

 network 1.0.0.0 0.255.255.255 area 1

!

ip classless

!

ip flow-export version 9

!

no cdp run

!

end







**** Below is the configuration for the Backbone internal Router A:

hostname Router

no ip cef

no ipv6 cef

spanning-tree mode pvst

!

interface FastEthernet0/0

 ip address 10.1.1.1 255.255.255.0

!

interface FastEthernet0/1

 ip address 10.1.2.1 255.255.255.0

!

router ospf 24

 log-adjacency-changes

 network 10.0.0.0 0.255.255.255 area 0

!

ip classless

ip flow-export version 9

end







**** Below is the configuration for NSSA ASBR (Router C 

hostname Router

no ip cef

no ipv6 cef

spanning-tree mode pvst

!

interface FastEthernet0/0

 ip address 1.1.1.2 255.255.255.0

!

interface FastEthernet0/1

 ip address 172.16.1.1 255.255.255.0

 !

router ospf 24

 log-adjacency-changes

 area 1 nssa

 redistribute rip subnets

 network 1.0.0.0 0.255.255.255 area 1

!

router rip

 redistribute ospf 24

 network 172.16.0.0

ip classless

ip flow-export version 9

end

!







**** Below is the configuration for the RIP Router 

hostname Router

no ip cef

no ipv6 cef

spanning-tree mode pvst

!

interface FastEthernet0/0

 ip address 172.16.1.2 255.255.255.0

 !

interface FastEthernet0/1

 ip address 172.16.2.1 255.255.255.0

 !

router rip

 network 172.16.0.0

!

ip classless

ip flow-export version 9

end










**** Here is the output “show ip route” for Router  ***********




Gateway of last resort is not set

     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks

C       172.16.1.0/24 is directly connected, FastEthernet0/0

L       172.16.1.2/32 is directly connected, FastEthernet0/0
















***** Here is the output “show ip route” for Router C: ***********




Gateway of last resort is not set

    1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C       1.1.1.0/24 is directly connected, FastEthernet0/0

L       1.1.1.2/32 is directly connected, FastEthernet0/0

O IA 10.0.0.0/8 [110/2] via 1.1.1.1, 02:13:08, FastEthernet0/0

     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks

C       172.16.1.0/24 is directly connected, FastEthernet0/1

L       172.16.1.1/32 is directly connected, FastEthernet0/1













****** Here is the output “show ip route” for Router B: ***********




Gateway of last resort is not set

     1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C       1.1.1.0/24 is directly connected, FastEthernet0/1

L       1.1.1.1/32 is directly connected, FastEthernet0/1

     10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C       10.1.2.0/24 is directly connected, FastEthernet0/0

L       10.1.2.2/32 is directly connected, FastEthernet0/0

     172.16.0.0/24 is subnetted, 1 subnets

O N2    172.16.1.0/24 [110/20] via 1.1.1.2, 01:56:15, FastEthernet0/1







**** Here is the output “show ip route” for Router A: ***********




Gateway of last resort is not set

     1.0.0.0/24 is subnetted, 1 subnets

O IA    1.1.1.0/24 [110/2] via 10.1.2.2, 02:11:36, FastEthernet0/1

     10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C       10.1.2.0/24 is directly connected, FastEthernet0/1

L       10.1.2.1/32 is directly connected, FastEthernet0/1

     172.16.0.0/24 is subnetted, 1 subnets

O E2    172.16.1.0/24 [110/20] via 10.1.2.2, 02:11:36, FastEthernet0/1

Much Appreciated for your good trouble shooting knowledge

[Georg Pauwen]

Hello,

I might be wrong, but I seem to recall that you cannot use the

area range

command in area 0. Try area 1 for that range, the null route will show up....

[jwangCisco]

Thank you George.     

In the past, I had read it somewhere, published by Cisco, that it was acceptable practice to summarise routes from the backbone direction, into other non-backbone areas.  If I should come across it again, you bet, I am going to copy and paste that valuable document here. ( My memory might be wrong though, so please feel free to point me to the relevant Cisco article).....thanking you for your awesome speedy ray of light

[MHM Cisco World]

I think I get issue here 

in router B and all router the wildcard is config wrong 

interface FastEthernet0/0

 ip address 10.1.2.2 255.255.255.0<-mask 

!

router ospf 24

 log-adjacency-changes

 area 0 range 10.0.0.0 255.0.0.0

 area 1 nssa

 network 10.0.0.0 0.255.255.255 area 0<<--here wildcard must us not mask so it must be 0.0.0.255, this i think make area range not work.

[jwangCisco]

I like your thinking MHM, so I had labbed it up, but the Summary Null route was still missing in action from the ABR's table... thank you with gratitude

[MHM Cisco World]

sorry I don't have PKT in my Mac, 

I TEST it in GNS3 even wrong wildcard the summary appear. 

so as @David Ruess test it is bug.

[Georg Pauwen]

Odd. I just recreated the topology, and now it works as predicted:

RouterB

router ospf 1
router-id 1.1.1.1
area 0 range 10.0.0.0 255.0.0.0
network 1.1.1.1 0.0.0.0 area 1
network 10.0.0.0 0.255.255.255 area 0

RouterB#sh ip route

Gateway of last resort is not set

1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
10.0.0.0/8 is variably subnetted, 3 subnets, 3 masks
O 10.0.0.0/8 is a summary, 00:00:58, Null0
C 10.1.2.0/30 is directly connected, GigabitEthernet0/0
L 10.1.2.1/32 is directly connected, GigabitEthernet0/0

[David Ruess]

Great. I was just about to upload my files as well. At least I got some practice configuring OSPF summary

I was able to re-create it in packet tracer and GNS3. I'm sure you're good but if you still want the files let me know. 

I will say in packet tracer it was a bit buggy. I had to reload the routers and wait another minute or 2 before it showed the summary route which I thought was weird. And another minute before it showed up on the router C downstream. 

-David

[MHM Cisco World]

same as Me, still this issue from my side need more deep study wildcard and area range and NSSA and area 0.
later if I get any update I will share it here.

[David Ruess · Accepted solution]

Hello,

According to your output it should work. To test it I also labbed up your example (minus extra configs and RIP router since it was irrelevant). I was able to produce a summary route of Null0. It may be just a buggy Packet tracer. Try configuring from scratch again (just the OSPF routers) or maybe do a reload. 

Another indicator you at least know summarization is working by the output of RouterC. It would see both 10.1.0.0 networks from Router A. The fact it sees only one as a /8 means your summary is getting downstream.

Hope that helps

-David

[Georg Pauwen]

@David Ruess Do you care posting your configs ? For some weird reason, in GNS3, I could not get a null route for area 0, as soon as I changed it to any other area, the null route appeared right away...