Re: Type-5 Default Route vs Summary Default Route in NSSA

It's a loop prevention mechanism. ABR will not install any summary
(Type 3) routes from non-backbone areas.

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Marko Milivojevic - CCIE #18427
Senior Technical Instructor - IPexpert
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On Wed, Aug 24, 2011 at 08:57, nhatphuc <nhatphuc_at_gmail.com> wrote:
> Hi all,
>
> I have a router connected to Area 0 and Area 3 NSSA
>
> This router receive 2 default route:
>
> Route via Area 3:
>
> O*IA B 0.0.0.0/0 [110/14] via 172.20.1.1, 01:04:19, GigabitEthernet0/2
>
> router# sh ip ospf database summary 0.0.0.0
>
> B  B  B  B  B OSPF Router with ID (1.1.1.1) (Process ID 1)
>
> B  B  B  B  B  B  B  B Summary Net Link States (Area 3)
>
> B LS age: 21
> B Options: (No TOS-capability, DC, Upward)
> B LS Type: Summary Links(Network)
> B Link State ID: 0.0.0.0 (summary Network Number)
> B Advertising Router: 10.16.255.5
> B LS Seq Number: 800000A6
> B Checksum: 0xF47C
> B Length: 28
> B Network Mask: /0
> B  B  B  B MTID: 0 B  B  B  B  Metric: 1
>
> B Routing Bit Set on this LSA in topology Base with MTID 0
> B LS age: 256
> B Options: (No TOS-capability, DC, Upward)
> B LS Type: Summary Links(Network)
> B Link State ID: 0.0.0.0 (summary Network Number)
> B Advertising Router: 10.16.255.6
> B LS Seq Number: 800000A5
> B Checksum: 0xF080
> B Length: 28
> B Network Mask: /0
> B  B  B  B MTID: 0 B  B  B  B  Metric: 1
>
> Route via Area 0
>
> O*E2 B 0.0.0.0/0 [110/20] via 10.16.0.1, 00:00:01, Tunnel1
>
> B  B  B  B  B  B OSPF Router with ID (1.1.1.1) (Process ID 1)
>
> B  B  B  B  B  B  B  B Type-5 AS External Link States
>
> B LS age: 1130
> B Options: (No TOS-capability, DC)
> B LS Type: AS External Link
> B Link State ID: 0.0.0.0 (External Network Number )
> B Advertising Router: 10.16.255.5
> B LS Seq Number: 8000000E
> B Checksum: 0xCBA4
> B Length: 36
> B Network Mask: /0
> B  B  B  B Metric Type: 2 (Larger than any link state path)
> B  B  B  B MTID: 0
> B  B  B  B Metric: 20
> B  B  B  B Forward Address: 10.18.3.227
> B  B  B  B External Route Tag: 1
>
> B Routing Bit Set on this LSA in topology Base with MTID 0
> B LS age: 313
> B Options: (No TOS-capability, DC)
> B LS Type: AS External Link
> B Link State ID: 0.0.0.0 (External Network Number )
> B Advertising Router: 10.16.255.6
> B LS Seq Number: 80000001
> B Checksum: 0xFA84
> B Length: 36
> B Network Mask: /0
> B  B  B  B Metric Type: 2 (Larger than any link state path)
> B  B  B  B MTID: 0
> B  B  B  B Metric: 20
> B  B  B  B Forward Address: 0.0.0.0
> B  B  B  B External Route Tag: 1
>
> The Router prefer O*E2 route over O*IA route.
>
> Why is it so? I think it should prefer O*IA over O*E2
>
> Can you help me explain this?
>
> Thank you,
>
> NP
>
>
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