OSPF Summarization

[DragosMariusAvram66611]

Hello everyone,

Regarding ospf summarization, please correct and advise me:

area 15 range summary-address mask.  this will advertise my summary address from area 15 into backbone. and is done on abr.

internet------asbr(area15)-------(area15)abr(area0)------rest of the network.

i dont want the asbr to see all the routes comming in from backbone, i just want to send a summary int area 15. 

Thank you in advance. 

[Jon Marshall · Accepted solution]

You are right, that is what the area range command does but it is not clear what you want to do. 

Are you trying to summarize area 15 to the rest of your OSPF network or are you trying to send a summary route into area 15 ? 

If the former then area range is the command to use, if the latter you need to make area 15 a totally NSSA.

Jon

[DragosMariusAvram66611]

Thank you for your prompt answer.

I am trying to have only one summary route into area 15 from area 0. On the absr which is in area 15 i want to have only the default route towards the internet, and a summary route 10.1.0.0/16 towards my internal network. 

As well sw1 must see a default gateway via 10.1.15.0

Thank you. 

[AliDoskii]

Hello

area 0 range 172.16.0.0 255.255.0.0

This will summary address 172.16.0.0 255.255.0.0 into backbone and everything happens on ABR.

if you want to summary anything into internet you have to do on ASBR by below command:

summary-address 172.16.0.0 255.255.0.0

[paul driver]

Hello

As the internet gateway reside in area 15 you could configure area 15 as a NSSA this will allow the advertisement of type 1,2,3 lsas but filter any external routes.from the backbone

(area15)abr(area0)

router xx
area 15 nssa

[MHM Cisco World]

that why we need T-NSSA, config Area 15 as T-NSSA will make your area only know LSA3 0.0.0.0 from backbone area. 
no need summary.

[jwangCisco]

Hi Experts,

I have a similar question.

mmm... Just a 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 below :

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 's 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