07-04-2022 02:46 AM - last edited on 07-05-2022 11:03 AM by Translator
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
Solved! Go to Solution.
07-04-2022 08:14 AM
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
07-04-2022 03:41 AM - last edited on 07-05-2022 11:05 AM by Translator
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....
07-05-2022 05:17 AM - edited 07-05-2022 05:26 AM
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
07-04-2022 05:37 AM - last edited on 07-05-2022 11:06 AM by Translator
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.
07-05-2022 04:59 AM - edited 07-05-2022 05:28 AM
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
07-05-2022 07:06 AM
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.
07-05-2022 02:06 PM
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
07-05-2022 03:22 PM
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
07-05-2022 04:02 PM
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.
07-04-2022 08:14 AM
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
07-05-2022 01:25 PM
@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...
07-05-2022 01:28 PM