OSPF Summarization within Area 0

Discussion in 'Cisco' started by ciscortp@hotmail.com, May 27, 2006.

  1. Guest

    Is it possible to use the area range command to summarize routes if you
    only have area 0. For example if I have area 0 with the subnets
    10.0.0.0 /26 and 10.0.0.64 /26. Can I perform the following:

    area 0 range 10.0.0.0 255.255.254.0

    What will this cause? Is this legal? Keep in mind that Area 0 is the
    only area that exists.

    Thanks.
     
    , May 27, 2006
    #1
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  2. stephen Guest

    <> wrote in message
    news:...
    > Is it possible to use the area range command to summarize routes if you
    > only have area 0. For example if I have area 0 with the subnets
    > 10.0.0.0 /26 and 10.0.0.64 /26. Can I perform the following:
    >
    > area 0 range 10.0.0.0 255.255.254.0
    >
    > What will this cause? Is this legal? Keep in mind that Area 0 is the
    > only area that exists.


    it shouldnt have any effect (if the router even allows you to configure it).
    Summaries are only used on ABRs and only affect the routes propagated across
    an area boundary.

    1 possible workaround is not to set up OSPF on those subnets and summarise
    the routes during redistribution into OSPF.
    - the summary is then an external rather than an internal summary (so
    handling is different in some ways)
    - only useful if 1 or more routers are connected to the set of subnets,
    statics etc.
    - not feasible if 1 or more of the subnets are links between routers where
    you need OSPF adjacencies.
    >
    > Thanks.
    >

    --
    Regards

    - replace xyz with ntl
     
    stephen, May 27, 2006
    #2
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  3. Guest

    The challenge is that There are Mainframes that Are forming Ospf
    Adjacencies with our routers, but the mainframes are generating Virtual
    IPs (/32 host routes That don't exist on any links to the manframe).
    We do not want to advertise all of these host routes so we would like
    to summarize them. The problem is that we must use only area 0.
    Another solution is to make the Mainframe their own stub area, then
    perform the summarization into area 0, but this is not an option for
    us. Please see below

    Virtual IP
    addresses===1.1.1.X/32====Mainframe-2.2.2.1/30====2.2.2.2/30-Router1

    >From my drawing all devices are in ospf area 0. An adjacency is

    formed between the Mainframe and the Router on the 2.2.2.0/30 subnet.
    The 1.1.1.X/32 (Virtual addresses) routes are going to originate from
    behind the Mainframe. Any way to summarize the 1.1.1.X/32's into a
    /24 using OSPF
     
    , May 27, 2006
    #3
  4. stephen Guest

    <> wrote in message
    news:...
    > The challenge is that There are Mainframes that Are forming Ospf
    > Adjacencies with our routers, but the mainframes are generating Virtual
    > IPs (/32 host routes That don't exist on any links to the manframe).
    > We do not want to advertise all of these host routes so we would like
    > to summarize them. The problem is that we must use only area 0.
    > Another solution is to make the Mainframe their own stub area, then
    > perform the summarization into area 0, but this is not an option for
    > us. Please see below
    >
    > Virtual IP
    > addresses===1.1.1.X/32====Mainframe-2.2.2.1/30====2.2.2.2/30-Router1
    >
    > >From my drawing all devices are in ospf area 0. An adjacency is

    > formed between the Mainframe and the Router on the 2.2.2.0/30 subnet.
    > The 1.1.1.X/32 (Virtual addresses) routes are going to originate from
    > behind the Mainframe. Any way to summarize the 1.1.1.X/32's into a
    > /24 using OSPF


    the only thing i can suggest is having 2 separate OSPF regions, and
    summarising between them.

    if the network design allows it, i would have 1 router connected to the
    mainframe, and 1 to the main OSPF network, then run BGP between them (or
    pairs if you need more resilience)

    in theory you can run 2 (or more) OSPF processes on 1 router, and
    redistribute.
    however - it seems to be "bargepole" technology last time i looked - i.e.
    lots of suggestions scattered aorund Cisco docs that says this is not
    recommended etc.

    good luck
    >

    --
    Regards

    - replace xyz with ntl
     
    stephen, May 27, 2006
    #4
  5. Merv Guest

    If you do not want or need /32 from the mainframe then have the system
    programmers reconfigure OMPROUTED accordingly.

    They may have configured VIPA's, however, if you only have a single
    mainframe these do not need to be broadcast into area 0. If you have
    redundant mainframes that require the use of VIPA's because the VIPA
    host routes will be announced over different links into area 0 then do
    not summarize.
     
    Merv, May 27, 2006
    #5
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