REPOST: OSPF Database Help

Discussion in 'Cisco' started by ccie2k4, Sep 6, 2006.

  1. ccie2k4

    ccie2k4 Guest

    Hi, can someone please help me in trying to understand the OSPF
    Database. Per my understanding the Database is structured per the
    Areas. Each Area will contain LSA's under it. I am confused as to what
    LSA's will appear under what area.
    For eg:

    1. The ASBR Summary LSA in the output below appears only under Area 51
    but in other topologies and output I have seen it appear under Area 0
    as well.


    2. Under the summary LSA I see 172.16.10.4 under the Area 0 section as
    well as the Area 51 section? Why is that.


    OSPF Router with ID (192.168.2.1) (Process ID 1)


    Router Link States (Area 0)


    Link ID ADV Router Age Seq#
    Checksum Link count
    172.16.10.5 172.16.10.5 751 0x8000000F
    0x6F9C 1
    192.168.1.1 192.168.1.1 540 0x80000012
    0x8D3D 1
    192.168.2.1 192.168.2.1 543 0x80000016
    0x7E46 1
    192.168.3.1 192.168.3.1 543 0x80000005
    0x9C36 1


    Net Link States (Area 0)


    Link ID ADV Router Age Seq#
    Checksum
    172.16.1.2 192.168.2.1 539 0x8000000D
    0xCFE8


    Summary Net Link States (Area 0)


    Link ID ADV Router Age Seq#
    Checksum
    172.16.10.4 192.168.3.1 617 0x80000001
    0xD126
    172.16.20.0 192.168.3.1 617 0x80000001
    0xA746
    172.16.51.1 192.168.2.1 544 0x80000005
    0xA832


    Router Link States (Area 51)
    Link ID ADV Router Age Seq#
    Checksum Link count
    192.168.2.1 192.168.2.1 585 0x8000000B
    0x855 1


    Summary Net Link States (Area 51)


    Link ID ADV Router Age Seq#
    Checksum
    172.16.1.0 192.168.2.1 531 0x80000001
    0xE22F
    172.16.10.4 192.168.2.1 531 0x80000001
    0xE215
    172.16.20.0 192.168.2.1 531 0x80000001
    0xB835


    Summary ASB Link States (Area 51)


    Link ID ADV Router Age Seq#
    Checksum


    192.168.1.1 192.168.2.1 531 0x80000001
    0x9EC4


    Type-5 AS External Link States


    Link ID ADV Router Age Seq#
    Checksum Tag
    11.0.0.0 192.168.1.1 988
    0x80000001 0x3FEA 0
    12.0.0.0 192.168.1.1 988
    0x80000001 0x32F6 0
    13.0.0.0 192.168.1.1 988
    0x80000001 0x2503 0


    In addition say if i look at the sho ip ospf data asbr-summary output
    and see that for LSA's appearing under Area 51 it gives the message the

    advertising router is not reachable. However I see the route to the
    advertising router in my routing table and am able to ping it as well.
    Could it be that the area 51 is upstream to the router I am looking at
    and hence because its upstream it doesn't make sense to put this
    routers LSA in the routing table since that would cause a routing loop
    and that is the reason why it says "Adv Router is not-reachable"
     
    ccie2k4, Sep 6, 2006
    #1
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  2. ccie2k4

    Guest

    ccie2k4 wrote:
    > Hi, can someone please help me in trying to understand the OSPF
    > Database. Per my understanding the Database is structured per the
    > Areas. Each Area will contain LSA's under it. I am confused as to what
    > LSA's will appear under what area.
    > For eg:
    >
    > 1. The ASBR Summary LSA in the output below appears only under Area 51
    > but in other topologies and output I have seen it appear under Area 0
    > as well.
    >
    >
    > 2. Under the summary LSA I see 172.16.10.4 under the Area 0 section as
    > well as the Area 51 section? Why is that.
    >
    >
    > OSPF Router with ID (192.168.2.1) (Process ID 1)
    >
    >
    > Router Link States (Area 0)
    >
    >
    > Link ID ADV Router Age Seq#
    > Checksum Link count
    > 172.16.10.5 172.16.10.5 751 0x8000000F
    > 0x6F9C 1
    > 192.168.1.1 192.168.1.1 540 0x80000012
    > 0x8D3D 1
    > 192.168.2.1 192.168.2.1 543 0x80000016
    > 0x7E46 1
    > 192.168.3.1 192.168.3.1 543 0x80000005
    > 0x9C36 1
    >
    >
    > Net Link States (Area 0)
    >
    >
    > Link ID ADV Router Age Seq#
    > Checksum
    > 172.16.1.2 192.168.2.1 539 0x8000000D
    > 0xCFE8
    >
    >
    > Summary Net Link States (Area 0)
    >
    >
    > Link ID ADV Router Age Seq#
    > Checksum
    > 172.16.10.4 192.168.3.1 617 0x80000001
    > 0xD126
    > 172.16.20.0 192.168.3.1 617 0x80000001
    > 0xA746
    > 172.16.51.1 192.168.2.1 544 0x80000005
    > 0xA832
    >
    >
    > Router Link States (Area 51)
    > Link ID ADV Router Age Seq#
    > Checksum Link count
    > 192.168.2.1 192.168.2.1 585 0x8000000B
    > 0x855 1
    >
    >
    > Summary Net Link States (Area 51)
    >
    >
    > Link ID ADV Router Age Seq#
    > Checksum
    > 172.16.1.0 192.168.2.1 531 0x80000001
    > 0xE22F
    > 172.16.10.4 192.168.2.1 531 0x80000001
    > 0xE215
    > 172.16.20.0 192.168.2.1 531 0x80000001
    > 0xB835
    >
    >
    > Summary ASB Link States (Area 51)
    >
    >
    > Link ID ADV Router Age Seq#
    > Checksum
    >
    >
    > 192.168.1.1 192.168.2.1 531 0x80000001
    > 0x9EC4
    >
    >
    > Type-5 AS External Link States
    >
    >
    > Link ID ADV Router Age Seq#
    > Checksum Tag
    > 11.0.0.0 192.168.1.1 988
    > 0x80000001 0x3FEA 0
    > 12.0.0.0 192.168.1.1 988
    > 0x80000001 0x32F6 0
    > 13.0.0.0 192.168.1.1 988
    > 0x80000001 0x2503 0
    >
    >
    > In addition say if i look at the sho ip ospf data asbr-summary output
    > and see that for LSA's appearing under Area 51 it gives the message the
    >
    > advertising router is not reachable. However I see the route to the
    > advertising router in my routing table and am able to ping it as well.
    > Could it be that the area 51 is upstream to the router I am looking at
    > and hence because its upstream it doesn't make sense to put this
    > routers LSA in the routing table since that would cause a routing loop
    > and that is the reason why it says "Adv Router is not-reachable"


    Thing is that this is quite involved, you really need to
    study this yourself.

    I certainly can't conjour up much in a few minutes.

    Maybe someone can recommend a good book?

    I have been working with ospf in a small way in LANs for years
    and had no idea what any of this meant however I have
    been doing more work recently and am beginning to
    get a bit of a clue. I was unable to make progress
    with books and need hands on.

    If you have specific questions you could try posing those.

    Sorry.

    ccie2k4 ? Aiming for your ccie in year 2400?
     
    , Sep 6, 2006
    #2
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