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

Hiya,

I have this question in my Anki Flashcards, I'm pretty sure I stole it from
a thread where Scott Morris was assisting with the answer, so I believe its
pretty accurate coz that guy is well freakin smart!

1. OSPF Intra Area Routes
2. OSPF Inter Area Routes
3. N1 & E1 are preferred over N2 & E2 for the same route
2. When N1 & E1 have the same route to the destination, The one that have
lower cost / Metric will win and get into the route table
3. If both N1 & E1 have the same cost, P-bit in N1 will be used to break the
tide.
4. If P-bit is 0 (Then it would become E1) then we will have 2 E1 routes
install into the routing table. (otherwise if maximum-path = 1, LSA with
Higher Router-ID will get installed)

On Thu, Oct 28, 2010 at 2:04 PM, Maarten Vervoorn <mr.vervoorn_at_gmail.com>wrote:

> Can you send me the config of R1 and R2 Only interface and ospf config.
> Also: "show ip ospf" on r1 and r2
> I still think R2 is the type5 type7 translator. Can you debug the ospf lsa
> on R1 to check where it reveives those updates from
>
> Kind regards,
>
> Maarten Vervoorn
>
> 2010/10/28 sp-ie m <sp.ccie.me_at_gmail.com>
>
> > 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.
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
> > _______________________________________________________________________
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>
>
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Received on Thu Oct 28 2010 - 22:35:05 ART