NSSA No Type 7/5 translation

Hello experts,

I have one scenario in INE Lab : ospf-nssa-type-7-to-type-5-translator

The route 160.1.10.10 is redis redistributed in NSSA AREA 1, but there are some values that are not correct according to the configuracion:

1.the route is redistribute as LSA 7 and LSA5.

2. The LSA7  has the Pbit=0 (No Type 7/5 translation) and FA is Zero.

Please your explanation about it, in other scenarios I do the same and dont have these outputs.

=================

R6#show run

router ospf 1
 router-id 150.1.6.6
 area 1 nssa
 redistribute connected subnets route-map CONNECTED->OSPF
 network 150.1.0.0 0.0.255.255 area 1
 network 155.1.0.0 0.0.255.255 area 1
!
route-map CONNECTED->OSPF permit 10

 match interface Loopback100

interface Loopback100
 ip address 160.1.6.6 255.255.255.255

 

In R6, the route is created by LSA5 and LSA7.

                Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag
160.1.6.6       150.1.6.6       247         0x80000004 0x008DBE 0


                Type-7 AS External Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Tag
160.1.6.6       150.1.6.6       231         0x80000002 0x0075D6 0

 

R6#show ip osp da nssa-external 160.1.6.6
            OSPF Router with ID (150.1.6.6) (Process ID 1)
                Type-7 AS External Link States (Area 1)
  LS age: 311
  Options: (No TOS-capability, No Type 7/5 translation, DC, Upward)
  LS Type: AS External Link
  Link State ID: 160.1.6.6 (External Network Number )
  Advertising Router: 150.1.6.6
  LS Seq Number: 80000001
  Checksum: 0x77D5
  Length: 36
  Network Mask: /32
        Metric Type: 2 (Larger than any link state path)
        MTID: 0
        Metric: 20
        Forward Address: 0.0.0.0
        External Route Tag: 0

R6(config)#DO SHOW IP OSPf DA EX 160.1.6.6
            OSPF Router with ID (150.1.6.6) (Process ID 1)
                Type-5 AS External Link States
  LS age: 493
  Options: (No TOS-capability, DC, Upward)
  LS Type: AS External Link
  Link State ID: 160.1.6.6 (External Network Number )
  Advertising Router: 150.1.6.6
  LS Seq Number: 80000004
  Checksum: 0x8DBE
  Length: 36
  Network Mask: /32
        Metric Type: 2 (Larger than any link state path)
        MTID: 0
        Metric: 20
        Forward Address: 0.0.0.0
        External Route Tag: 0

R5 which is in other area, area 0 it see the route external has connectivity.

R5#show ip ospf database external 160.1.6.6

            OSPF Router with ID (150.1.5.5) (Process ID 1)

                Type-5 AS External Link States

  Routing Bit Set on this LSA in topology Base with MTID 0
  LS age: 1091
  Options: (No TOS-capability, DC, Upward)
  LS Type: AS External Link
  Link State ID: 160.1.6.6 (External Network Number )
  Advertising Router: 150.1.6.6
  LS Seq Number: 80000002
  Checksum: 0x91BC
  Length: 36
  Network Mask: /32
        Metric Type: 2 (Larger than any link state path)
        MTID: 0
        Metric: 20
        Forward Address: 0.0.0.0
        External Route Tag: 0

 

Comments

  • timaztimaz ✭✭

    Hi. according to the RFC 3101, while a router has to redistribute a route as both of the Type-7 and Type-5, it clears the P-bit and prevents ABR routers to translate them to type-5. the reason is, there is no need for translation and that is because the router that are responsible for redistribution, has created type-5 that will be available for whole OSPF domain anyway. 

  • thanks for your answer which is correct 

    Please correct my if I am Wrong but the correct behavior is R6 (ASBR) which only must create LSA7, the ABR (R4) is the one who made the translation LSA7-5 and this LSA 5 is flood to all the OSPF DOMAIN. Also R4 see that Adverting routers is R6 m but it could be R4.

    |-- AREA 1 -------||---AREA 0

    R6(ASBR)---R4 (ABR)-----R5

    In my scenario the behavior is diferrent: R6 generate LSA5 and LSA7 and R4 only forward the LSA5.

     

  • Yeah your entries don't make sense at all.

    I have just configured, almost the exact same network just to prove it. And currently my R6's routing table is below. Notice how no type 5 LSA exists for that route.

    R6#sh ip ospf da

                OSPF Router with ID (6.6.6.6) (Process ID 1)

                    Router Link States (Area 1)

    Link ID         ADV Router      Age         Seq#       Checksum Link count
    4.4.4.4         4.4.4.4         368         0x80000005 0x004CE6 2
    6.6.6.6         6.6.6.6         367         0x80000006 0x0086A2 2

                    Summary Net Link States (Area 1)

    Link ID         ADV Router      Age         Seq#       Checksum
    10.0.45.0       4.4.4.4         580         0x80000001 0x00A73E

                    Type-7 AS External Link States (Area 1)

    Link ID         ADV Router      Age         Seq#       Checksum Tag
    160.1.6.6       6.6.6.6         367         0x80000003 0x00ED90 0

     

     

     

  • Hi all,

    Great explanations on how this works.

    Check on R6:  show ip ospf

    and look to see whether Area BACKBONE(0) (Inactive) appears.

    Here is a (1) path to getting to 7s and 5s being advertised across nssa area. old 12.4 code

    R1--R2, R1 is ASBR, nssa link

    I'm not surprised that LSA5 is generated, but am surprised that it is flooded across nssa area.

    configure R1 with an interface in area 0, and then remove "ip opsf 1 area 0" from the interface.  This gets R1 to be an ASBR, and area 0 to be present but inactive.  Note that R2 is receiving an LSA 5 from R1 across an nssa area.

    R1#show ip ospf

     Routing Process "ospf 1" with ID 100.1.1.1

    <snip>

     It is an autonomous system boundary router

     Redistributing External Routes from,

        connected, includes subnets in redistribution

     Router is not originating router-LSAs with maximum metric

    <snip>

     Number of areas in this router is 2. 1 normal 0 stub 1 nssa

     Number of areas transit capable is 0

     External flood list length 0

     IETF NSF helper support enabled

     Cisco NSF helper support enabled

        Area BACKBONE(0) (Inactive)

    <snip>

        Area 1

            Number of interfaces in this area is 1

            It is a NSSA area

    <snip>

     

    R2#show ip os data external

                OSPF Router with ID (10.0.12.2) (Process ID 1)

                    Type-5 AS External Link States

      LS age: 101

      Options: (No TOS-capability, DC)

      LS Type: AS External Link

      Link State ID: 1.1.1.1 (External Network Number )

      Advertising Router: 10.0.12.2

      LS Seq Number: 80000001

      Checksum: 0x1855

      Length: 36

      Network Mask: /32

            Metric Type: 2 (Larger than any link state path)

            TOS: 0

            Metric: 20

            Forward Address: 10.0.12.1

            External Route Tag: 0

    ************

    My mistake.  overlooked advertising router is R2, which doing the 7/5 translation.  Must have been late at night.

    Cheers.

  • thank you for your answer, I was reading about it and it is correct. thank you very much

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