[e2e] Addressing format...network and mask
touch at ISI.EDU
Mon Dec 1 09:29:11 PST 2003
Michael B Greenwald wrote:
> Mon, 1 Dec 2003 13:51:47 +0530
> "Alok Dube" <alok.dube at apara.com>
> I need a way to propogate the 1st address and last address of a network.
> Incase i have 129 hosts in a network, i simply should propogate the 1st
> address and the last address (or the number of hosts) instead of the mask.
> I'm not sure what you really need to do here, but if I understand
> somewhat correctly, then why not just allocate two subnets, one with
> 128 hosts and one with 1 host? If you are trying for a dense
> allocation of addresses within the net, then, in the absolute worst
> case, there will be 25% waste. Usually, it will be much more densely
> packed (no waste at all in your example of 129).
/25 subnets can't support 128 hosts; the max is 125. The result would be:
1 /25 subnet with 125 hosts
all 0's depricated
all 1's broadcast
one address for the router
1 /29 subnet with 3 hosts
That's 129/130 max possible (99.2% efficient use of host addresses),
though it's only 94.9% efficient with the space as a whole.
However, if you've got 129 hosts and you're using a /24, you're not
doing badly at all.
The first address/last address method isn't as useful because it doesn't
communicate the routing information, i.e., first and last of the 129
could be a (/25, /29) pair, or a single (/24), or many other combinations.
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