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Hello-am unsure whether this is valid
If I use a class C address and use the first subnet with a /26 mask
> > 2nd subnet uses /27
> > 3rd subnet uses /28
> > 4th subnet uses /29
> >
> > which if I am correct takes me to .120
> >
> > can I then use a /26 address again? taking me to .184 ?
> >Or do I have to use /30 from then on?
> > TIA

In article < om>,
"daytime" <> wrote:

> Hello-am unsure whether this is valid
> If I use a class C address and use the first subnet with a /26 mask
> > > 2nd subnet uses /27
> > > 3rd subnet uses /28
> > > 4th subnet uses /29
> > >
> > > which if I am correct takes me to .120
> > >
> > > can I then use a /26 address again? taking me to .184 ?
> > >Or do I have to use /30 from then on?
> > > TIA

You can use a /26, but it has to start at a multiple of 64, so the
available ones are .128/26 and .192/26.

--
Barry Margolin,
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***

I understand-is it possible to start off with a /30 address and then
work backwards ?
example -- /29 /28 /27 /26

0-3
4-11
12-27
28-59
60-124 ?

I am trying to cut down on wasting addresses-or is this just the nature
of the beast?

btw many thanks for answering.
Barry Margolin wrote:
> In article < om>,
> "daytime" <> wrote:
>
> > Hello-am unsure whether this is valid
> > If I use a class C address and use the first subnet with a /26 mask
> > > > 2nd subnet uses /27
> > > > 3rd subnet uses /28
> > > > 4th subnet uses /29
> > > >
> > > > which if I am correct takes me to .120
> > > >
> > > > can I then use a /26 address again? taking me to .184 ?
> > > >Or do I have to use /30 from then on?
> > > > TIA
>
> You can use a /26, but it has to start at a multiple of 64, so the
> available ones are .128/26 and .192/26.
>
> --
> Barry Margolin,
> Arlington, MA
> *** PLEASE post questions in newsgroups, not directly to me ***
> *** PLEASE don't copy me on replies, I'll read them in the group ***

In article <. com>, "daytime" <> writes:
> I understand-is it possible to start off with a /30 address and then
> work backwards ?
> example -- /29 /28 /27 /26
>
> 0-3

Yes, that's fine. But that's a /30.

> 4-11

That's not fine. That's a /29 (8 hosts) but it's aligned on a /30
(multiple of 4) boundary. Try 8-15 instead.

> 12-27

That's not fine. That's a /28 aligned on a /30 boundary. Use 16-31

> 28-59

And that's a /27 aligned on a /30 boundary. Use 32-63

> 60-124 ?

That's a /26 aligned on a /30 boundary. Use 64-127

If your subnet size is 2^n then it has to start on a 2^n boundary.

You can carve the space up any way you please as long as you stick
to that rule.

There are sixteen ways to carve a /25 up into a /26, a /27, a /28,
a /29 and two /30's.

[Where do you want the /26 -- low half 0-63 or high half 64-127?
Given that, where do you want the /27 -- low half or high half?
Given that, where do you want the /28 -- low half or high half?
Given that, where do you want the /29 -- low half or high half?
Given that, the remaining space gets split into the two /30's]

wrote:
> In article <. com>, "daytime" <> writes:
> > I understand-is it possible to start off with a /30 address and then
> > work backwards ?
> > example -- /29 /28 /27 /26
> >
> > 0-3
>
> Yes, that's fine. But that's a /30.
>
> > 4-11
>
> That's not fine. That's a /29 (8 hosts) but it's aligned on a /30
> (multiple of 4) boundary. Try 8-15 instead.
>
> > 12-27
>
> That's not fine. That's a /28 aligned on a /30 boundary. Use 16-31
>
> > 28-59
>
> And that's a /27 aligned on a /30 boundary. Use 32-63
>
> > 60-124 ?
>
> That's a /26 aligned on a /30 boundary. Use 64-127
>
> If your subnet size is 2^n then it has to start on a 2^n boundary.
>
> You can carve the space up any way you please as long as you stick
> to that rule.
>
> There are sixteen ways to carve a /25 up into a /26, a /27, a /28,
> a /29 and two /30's.
>
> [Where do you want the /26 -- low half 0-63 or high half 64-127?
> Given that, where do you want the /27 -- low half or high half?
> Given that, where do you want the /28 -- low half or high half?
> Given that, where do you want the /29 -- low half or high half?
> Given that, the remaining space gets split into the two /30's]

Its just clicked now!!

If I start with a /30 then I must use at least 2 subnets (to avoid
wastage) before going on to the /29.

Whereas if I start off big -/26 ,I can then "carve up "(nice
description) the next subnet.

Many many thanks for clearing that up--I dont work in IT yet ,but in
your experience how are
subnets usually worked out?
Is it Big to Small or vice versa.?

TIA

In article < om>,
"daytime" <> wrote:

> Hello-am unsure whether this is valid
> If I use a class C address and use the first subnet with a /26 mask
> > > 2nd subnet uses /27
> > > 3rd subnet uses /28
> > > 4th subnet uses /29
> > >
> > > which if I am correct takes me to .120
> > >
> > > can I then use a /26 address again? taking me to .184 ?
> > >Or do I have to use /30 from then on?
> > > TIA

This may help (there are plenty of similar things around, just that this
is the one I made myself).

<http://www.ucs.ed.ac.uk/~ercm20/byte-table.html>

Sam

Sam Wilson wrote:
> In article < om>,
> "daytime" <> wrote:
>
> > Hello-am unsure whether this is valid
> > If I use a class C address and use the first subnet with a /26 mask
> > > > 2nd subnet uses /27
> > > > 3rd subnet uses /28
> > > > 4th subnet uses /29
> > > >
> > > > which if I am correct takes me to .120
> > > >
> > > > can I then use a /26 address again? taking me to .184 ?
> > > >Or do I have to use /30 from then on?
> > > > TIA
>
> This may help (there are plenty of similar things around, just that this
> is the one I made myself).
>
> <http://www.ucs.ed.ac.uk/~ercm20/byte-table.html>
>
> Sam

Thanks alot for that-very easy to understand.
Will be using it for along time to come !