RE: area 1 nssa default-information-originate no-summary

Yes this is true.

No summary = stub area = no redistribution of static or other externals is possible. So to exit the OSPF area , you NEED a default to the ABR. There is no other exit point. Therefore, it is automatically generated in a stub area.
Nssa = redistribution of external routes is still possible in this case, you might connect a RIP or BGP domain to a NSSA area. You might want to point your default to this bgp or RIP domain. Therefore, cisco
can't "assume" anymore you want to exit via OSPF ABR. Therefore, the default is not automatically generated in nssa, you must configure it specifically by adding "default-information-originate"

Geert
CCIE#13792

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of john matijevic
Sent: zaterdag 14 april 2012 16:29
To: Marko Milivojevic
Cc: Tom Kacprzynski; Cisco certification
Subject: Re: area 1 nssa default-information-originate no-summary

Good Afternoon Tom,

After labbing it up we can see what happens when we use the following:

I have R2 and R6 in this example in area 3 NSSA, R6 is the ABR and is configured with the following:

 area 3 nssa default-information-originate

If I look at the following routing table on R2:

I get the following:

R2#show ip route ospf
O N2 204.12.2.0/24 [110/20] via 110.1.100.6, 00:02:51, Serial0/0 O N2 204.12.3.0/24 [110/20] via 110.1.100.6, 00:02:51, Serial0/0 O N2 204.12.4.0/24 [110/20] via 110.1.100.6, 00:02:51, Serial0/0 O N2 204.12.5.0/24 [110/20] via 110.1.100.6, 00:02:51, Serial0/0
     110.0.0.0/8 is variably subnetted, 10 subnets, 3 masks
O IA 110.1.6.1/32 [110/65] via 110.1.100.6, 00:02:51, Serial0/0
O IA 110.1.0.6/32 [110/64] via 110.1.100.6, 00:02:51, Serial0/0
O IA 110.1.4.1/32 [110/129] via 110.1.100.6, 00:02:51, Serial0/0
O IA 110.1.5.1/32 [110/130] via 110.1.100.6, 00:02:51, Serial0/0
O IA 110.1.3.1/32 [110/129] via 110.1.100.6, 00:02:51, Serial0/0
O IA 110.1.1.1/32 [110/130] via 110.1.100.6, 00:02:51, Serial0/0
O IA 110.1.0.0/24 [110/192] via 110.1.100.6, 00:02:51, Serial0/0
O IA 110.1.145.0/24 [110/129] via 110.1.100.6, 00:02:51, Serial0/0
O N2 192.6.6.0/24 [110/20] via 110.1.100.6, 00:02:51, Serial0/0
     150.100.0.0/24 is subnetted, 2 subnets
O N2 150.100.1.0 [110/20] via 110.1.100.6, 00:02:53, Serial0/0
O*N2 0.0.0.0/0 [110/1] via 110.1.100.6, 00:02:53, Serial0/0

This tells me that not only it generates a default route but also advertises Interarea Routes.

Now let me go back to R6 and take out the default information originate.
Now I will just use the no-summary on R6.

O N2 204.12.2.0/24 [110/20] via 110.1.100.6, 00:00:56, Serial0/0 O N2 204.12.3.0/24 [110/20] via 110.1.100.6, 00:00:56, Serial0/0 O N2 204.12.4.0/24 [110/20] via 110.1.100.6, 00:00:56, Serial0/0 O N2 204.12.5.0/24 [110/20] via 110.1.100.6, 00:00:56, Serial0/0 O N2 192.6.6.0/24 [110/20] via 110.1.100.6, 00:00:56, Serial0/0
     150.100.0.0/24 is subnetted, 2 subnets
O N2 150.100.1.0 [110/20] via 110.1.100.6, 00:00:56, Serial0/0
O*IA 0.0.0.0/0 [110/65] via 110.1.100.6, 00:01:01, Serial0/0

Now I just have the default route but not the InterArea Routes.

Now I will go back to R6 put default-information-originate along with the no-summary

R2#show ip route ospf
O N2 204.12.2.0/24 [110/20] via 110.1.100.6, 00:00:19, Serial0/0 O N2 204.12.3.0/24 [110/20] via 110.1.100.6, 00:00:19, Serial0/0 O N2 204.12.4.0/24 [110/20] via 110.1.100.6, 00:00:19, Serial0/0 O N2 204.12.5.0/24 [110/20] via 110.1.100.6, 00:00:19, Serial0/0 O N2 192.6.6.0/24 [110/20] via 110.1.100.6, 00:00:19, Serial0/0
     150.100.0.0/24 is subnetted, 2 subnets
O N2 150.100.1.0 [110/20] via 110.1.100.6, 00:00:19, Serial0/0
O*IA 0.0.0.0/0 [110/65] via 110.1.100.6, 00:00:19, Serial0/0 R2#

Same output as before with just the no-summary option configured.

So to answer your question, based on observation there is no need to have default-information-originate when you have the no-summary command configured.

Regards,
John

On 4/14/12, Marko Milivojevic <markom_at_ipexpert.com> wrote:
> Today, it makes no sense. In the past (I recall 12.2(33)SXD) when they
> were both used a Type 3 default was suppressed and only Type 7 default
> route was generated.
>
> --
> Marko Milivojevic - CCIE #18427
>
> :: This message was sent from a mobile device. I apologize for errors
> and brevity. ::
>
> On Apr 13, 2012, at 19:47, Tom Kacprzynski <tom.kac_at_gmail.com> wrote:
>
>> Hello,
>> Does this command make sense? In what situation would you use
>> no-summary and default-information-originate at the same time? With
>> the no-summary option a LSA Type 3 default route is generated, so
>> what would the default-information-originate command do? I tried it
>> in a lab and it only generated a default LSA Type 3 based on the no-summary option.
>>
>> Can anyone think of a scenario where this would ever work or be used?
>>
>> Thank you,
>>
>> Tom
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
>> _____________________________________________________________________
>> __ Subscription information may be found at:
>> http://www.groupstudy.com/list/CCIELab.html
>
>
> Blogs and organic groups at http://www.ccie.net
>
> ______________________________________________________________________
> _ Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html

Blogs and organic groups at http://www.ccie.net
Received on Thu May 10 2012 - 21:29:57 ART