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  1. Rene,

    I have a doubt, all examples that you gave are "continuos" networks and an even number of networks.
    And when we have networks like below? I just can solve them with binary method. Is there another form?

    172.16.10.0/24
    172.16.20.0/24
    172.16.30.0/24
    172.16.40.0/24
    172.16.50.0/24

    I choosed shortest and highest networks and convert them to binary, so the summary address will be
    176.16.0.0/18 a block size 64 networks. I can't solve it using CIDR notation and block size method.

    Another example with an odd number of networks, I can solve it with binary method

    192.168.0.0 / 24
    192.168.1.0 / 24
    192.168.2.0 / 24
    192.168.3.0 / 24
    192.168.4.0 / 24

    The summary address will be 192.168.0.0/21, but when I was writing this example I saw that if I use block
    size it's able solve it too. It's need always think in block size like "powers of 2".

    When you have a free time, please, detail below

    8 + 8 + 6 = 24 bits

    Hug and thanks for yours articles. It's helping a lot :slight_smile:

  2. Hey Rene,
    I was following you example but got confused on these:
    172.1.4.0/25 10101100.00000001.00000100.00000000
    172.1.128.0/25 10101100.00000001.10000000.00000000
    172.1.5.0/24 10101100.00000001.00000101.00000000
    172.1.6.0/24 10101100.00000001.00000110.00000000
    172.1.7.0/24 10101100.00000001.00000111.00000000

    Particularly the 2nd one 172.1.128.0/25. Following your example using the 3rd octet has a 128 in it, so how would I factor this in as the other octets are using the first 5 bits.

    thanks
    James

  3. Hi James,

    Where did you find this example? It's not on this page? :slight_smile:

    Rene

  4. Hi Rene

    What are the disadvantages of using Route Summarization? Can you explain those with some examples pl.

  5. Hi Lokesh,

    There are a couple of potential issues.

    1) You can blackhole traffic. For example let's say you have these 4 networks behind a router:

    192.168.0.0 /24
    192.168.1.0 /24
    192.168.2.0 /24
    192.168.3.0 /24

    If you would create a summary like 192.168.0.0 /20 then basically you are advertising the 192.168.0.0 - 192.168.15.0 range to other routers. When your router receives a packet with destination 192.168.6.6 or something it will drop it.

    2) Asymmetric routing, This one is harder to explain with text only. When you advertise a summary it's possible that other routers will select a different (more specific) path as the next hop.

    3) Traffic engineering: If you use a routing protocol then you can play with the different metrics for each prefix. If you advertise a summary instead of all the different prefixes then you won't be able to change metric (or BGP attributes) for a single prefix.

    Rene

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