>I want to summarize three addresses within an OSPF area:
>
>10.2.1.0/24
>10.2.2.0/24
>10.2.3.0/24
>
>Converting to binary, I see the 15th bit is the highest order bit the three
>addresses have in common. From that I see the summary address is 10.2.0.0.
>What I don't understand is why the subnet mask is 16bits. To me it looks
>like it should be 15.
>
>Thanks,
>Steve
There's a widespread and unfortunate belief that "summarization" is
OK if it includes a list of addresses, even if it picks up addresses
not included in the list. True, you can probably get away with that
in many enterprise situations, but it can be catastrophic in the
Internet.
As I interpret the problem, the minimum number of addresses that can
be created from your example are:
10.2.1.0/24
10.2.2.0/23
You can't do the /22, because it would pick up 10.2.0.0/24, which
isn't part of the list.
/15 or /16 make no sense. Converting the third octet to binary:
10.2.0.0/24 000000 00
10.2.1.0/24 000000 01
10.2.2.0/24 000000 10
10.2.3.0/24 000000 11
^^^^^^ ^^
111222 22
789012 34
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=1814&t=1794
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