Re: Question - OSPF N and E route... (intra vs inter) **

  R1-R2 (12.1.1.0/24) in Area 0.
  R1-R3 (13.1.1.0/24) in Area 1
  R2-R4 (24.1.1.0/24) in Area 1
  R3-R4 (34.1.1.0/24)in Area1.

R1-----Area0-----R2
 | |

Area1 Area1
 | |
R3-----Area1-----R4

IP addresssing -
R1 = .1
R2 = .2
R3 =.3
R4 = .4

Router IDs -
R1 = 1.1.1.1
R2 = 2.2.2.2
R3 = 3.3.3.3
R4 = 4.4..4.4

Logs:

R3#o d ns 134.1.1.0
R3#sh ip ospf d ns 134.1.1.0

OSPF Router with ID (3.3.3.3) (Process ID 1)

Type-7 AS External Link States (Area 1)

LS age: 111
Options: (No TOS-capability, Type 7/5 translation, DC)
LS Type: AS External Link
Link State ID: 134.1.1.0 (External Network Number )
Advertising Router: 3.3.3.3
LS Seq Number: 80000001
Checksum: 0x2056
Length: 36
Network Mask: /24
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 20
Forward Address: 3.3.3.3
External Route Tag: 0

Routing Bit Set on this LSA
LS age: 116
Options: (No TOS-capability, Type 7/5 translation, DC)
LS Type: AS External Link
Link State ID: 134.1.1.0 (External Network Number )
Advertising Router: 4.4.4.4
LS Seq Number: 80000001
Checksum: 0xB736
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 4.4.4.4
External Route Tag: 0

R3#

R4#o d ns 134.1.1.0
R4#sh ip ospf d ns 134.1.1.0

OSPF Router with ID (4.4.4.4) (Process ID 1)

Type-7 AS External Link States (Area 1)

Routing Bit Set on this LSA
LS age: 60
Options: (No TOS-capability, Type 7/5 translation, DC)
LS Type: AS External Link
Link State ID: 134.1.1.0 (External Network Number )
Advertising Router: 3.3.3.3
LS Seq Number: 80000001
Checksum: 0x2056
Length: 36
Network Mask: /24
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 20
Forward Address: 3.3.3.3
External Route Tag: 0

LS age: 65
Options: (No TOS-capability, Type 7/5 translation, DC)
LS Type: AS External Link
Link State ID: 134.1.1.0 (External Network Number )
Advertising Router: 4.4.4.4
LS Seq Number: 80000001
Checksum: 0xB736
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 4.4.4.4
External Route Tag: 0

R4#

R1#sir 134.1.1.0 l
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

134.1.0.0/24 is subnetted, 1 subnets
O E1 134.1.1.0 [110/85] via 13.1.1.3, 00:02:02, Serial1/1

R1#o d ns 134.1.1.0
R1#sh ip ospf d ns 134.1.1.0

  OSPF Router with ID (1.1.1.1) (Process ID 1)

Type-7 AS External Link States (Area 1)

LS age: 466
Options: (No TOS-capability, Type 7/5 translation, DC)
LS Type: AS External Link
Link State ID: 134.1.1.0 (External Network Number )
Advertising Router: 3.3.3.3
LS Seq Number: 80000001
Checksum: 0x2056
Length: 36
Network Mask: /24
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 20
Forward Address: 3.3.3.3
External Route Tag: 0

LS age: 471
Options: (No TOS-capability, Type 7/5 translation, DC)
LS Type: AS External Link
Link State ID: 134.1.1.0 (External Network Number )
Advertising Router: 4.4.4.4
LS Seq Number: 80000001
Checksum: 0xB736
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 4.4.4.4
External Route Tag: 0

R1#o d ex 134.1.1.0
R1#sh ip ospf d ex 134.1.1.0

  OSPF Router with ID (1.1.1.1) (Process ID 1)

Type-5 AS External Link States

Routing Bit Set on this LSA
LS age: 447
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 134.1.1.0 (External Network Number )
  Advertising Router: 2.2.2.2
LS Seq Number: 80000001
Checksum: 0xEA0F
Length: 36
Network Mask: /24
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 20
Forward Address: 3.3.3.3
External Route Tag: 0

R1#

R2#sir 134.1.1.0 l
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

134.1.0.0/24 is subnetted, 1 subnets
O N1 134.1.1.0 [110/149] via 24.1.1.4, 00:06:47, Serial1/1
R2#
R2#o d ex 134.1.1.0
R2#sh ip ospf d ex 134.1.1.0

  OSPF Router with ID (2.2.2.2) (Process ID 1)

Type-5 AS External Link States

LS age: 493
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 134.1.1.0 (External Network Number )
  Advertising Router: 2.2.2.2
LS Seq Number: 80000001
Checksum: 0xEA0F
Length: 36
Network Mask: /24
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 20
Forward Address: 3.3.3.3
External Route Tag: 0

R2#sh ip ospf d ns 134.1.1.0

  OSPF Router with ID (2.2.2.2) (Process ID 1)

Type-7 AS External Link States (Area 1)

Routing Bit Set on this LSA
LS age: 522
Options: (No TOS-capability, Type 7/5 translation, DC)
LS Type: AS External Link
Link State ID: 134.1.1.0 (External Network Number )
Advertising Router: 3.3.3.3
LS Seq Number: 80000001
Checksum: 0x2056
Length: 36
Network Mask: /24
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 20
Forward Address: 3.3.3.3
External Route Tag: 0

LS age: 527
Options: (No TOS-capability, Type 7/5 translation, DC)
LS Type: AS External Link
Link State ID: 134.1.1.0 (External Network Number )
Advertising Router: 4.4.4.4
LS Seq Number: 80000001
Checksum: 0xB736
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 4.4.4.4
External Route Tag: 0

On Wed, Oct 27, 2010 at 6:50 PM, sp-ie m <sp.ccie.me_at_gmail.com> wrote:
> Hey guys,
>
> I'm confused if Intra-area N1 will be left out and Inter-Area E1 will
> be chosen if E1 is seen from highest router-id NSSA ABR .
>
> I hv a square topology.
>
> Area 1 is NSSA.
>
> R1-----Area0-----R2
> | |
> Area1 Area1
> | |
> R3-----Area1-----R4
>
> R1-R2 in Area 0.
> R1-R3 in Area 1
> R2-R4 in Area 1
> R3-R4 in Area1.
>
> Router ID R1 = 1.1.1.1
> R2 = 2.2.2.2
> R3 = 3.3.3.3
> R4 = 4.4..4.4
>
> Question: Both R3 and R4 are redistributing a static route 134.1.1.0
> into Area1. R3 is redistributing it as N1 while R4 as N2.
> On R2, I can see it receives 134.1.1.0/24 as N1 from R4. This makes
> perfect sense as N1 is pref over N2.
>
> On R1, I can see it receives 134.1.1.0/24 as E1 route from R2 but the
> next hop is R3's interface IP. This part is tricky.
> Which rule says that E1 from Inter-area neighbor will supersede N1
> from local area?? I know this is somehow happening coz R4 has highest
> router-ID NSSA ABR but dont quite understand how intra-area N1 is left
> out and Inter-Area E1 is chosen.
>
> Tried a cursory look in few popular workbooks but didnt find similar issue.

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Received on Thu Oct 28 2010 - 02:19:04 ART