Sorry for overlooking you! Good job!
Mike W.
John Neiberger <[EMAIL PROTECTED]> wrote in message
32064763.962730060174.JavaMail.imail@tiptoe">news:32064763.962730060174.JavaMail.imail@tiptoe...
> Thanks, Evgeny. My answer had that mask 0.0.0.24, which would only allow
> specific hosts on a specific subnet. If the original question was to
allow
> any host witha 1,9,17, or 25 in the last octect--but from any subnet--then
> 255.255.255.24 would be the correct answer.
>
> It all depends on how the original question was worded. Regardless, the
> trickiest part was the mask on the last octect. Good question!!
> We need to make this a regular thing, that was a lot of fun.
>
> John
>
> > Michael,
> >
> > Thanks a lto for mentioning my name, but
> > I've just looked through follow-ups and found out that John Neiberger
was
> > the first to give correct answer.
> >
> > RGRDS,
> > EVgeny
> >
> > --
> > ***********
> > Please DO NOT send replies just directly to me, post them to the
> Newsgroup
> > as well
> >
> > ***********
> > ""Michael L. Williams"" <[EMAIL PROTECTED]> wrote in message
> > 8jt2kl$2s4$[EMAIL PROTECTED]">news:8jt2kl$2s4$[EMAIL PROTECTED]...
> > > Okay. There have been alot of responses to this. And alot of people
> > > wanting the answer.
> > >
> > > SO, let me mention Evgeny Babanin and Chuck Hwang, since they gave
> correct
> > > responses to the question! Congrats!!
> > >
> > > Now, I'll everyone's agony........... =)
> > >
> > > The answer is:
> > >
> > > access-list 10 permit A.B.C.1 255.255.255.24
> > >
> > > Here's the explanation:
> > >
> > > Remeber in the wildcard mask, for a given bit:
> > > 0 = must match the same bit in the source address given
> > > 1 = doesn't matter what it is........
> > >
> > > I will use A.B.C.1 for the source address in the access-list command
> since
> > > (as we see below) the least significant should always be 1. Below I
> have
> > > the binary version of our address 0.0.0.1:
> > >
> > > aaa aaa.bbb bbb.ccc ccc.0000 0001 <- least significant bit = 1, thus
> > > the decimal value of that octect is 1. This is crutial because this
is
> > the
> > > only non-zero bit in the source address. We'll use that later.
> > >
> > > Limiting ourselves to looking at the last octet of the target IPs we
> want
> > to
> > > let through,
> > > 0000 0001 = 1
> > > 0000 1001 = 9
> > > 0001 0001 = 17
> > > 0001 1001 = 25
> > > ---------------
> > > So since the last bit (xxxx xxx1) has to = 1 (like in the source
> address),
> > > it's corresponding wildcard bit must = 0
> > >
> > > so we know the wildcard mask so far has to be xxxx xxx0 (last octect
> > only)
> > >
> > > we also know that bits (from right to left) 2, 3, 6, 7, 8 HAVE to be
=
> 0
> > (so
> > > they match the zeros in the source address), so therefore their
> > > corresponding bits in the wildcard mask must be = 0. So now we have:
> > >
> > > 000x x000 (last octect only)
> > >
> > > When looking at bit 4 and 5 we see that they could be either 0 or 1.
> Any
> > of
> > > the
> > > four combinations of 0 and 1 give us the four target addresses, so
> > > their bits in the wildcard mask are = 1. So our final wildcard mask
> will
> > be
> > >
> > > 0001 1000 (last octect only) = 24 (decimal)
> > >
> > > So...... the following command is the correct answer:
> > >
> > > access-list 10 permit A.B.C.1 255.255.255.24
> > >
> > > It's a tough question,...... That's why it's fun =) Thanks to
everyone
> > that
> > > participated!
> > >
> > > Mike W.
> > >
> > > PS: Alrighty Chuck..... we're ready for the next question =)
> > >
> > > > Puzzle posed by Mike Williams:
> > > >
> > > > Make a (single line) access-list that will only allow traffic from
> > > addresses
> > > > matching the following model:
> > > >
> > > > x.x.x.1
> > > > x.x.x.9
> > > > x.x.x.17
> > > > x.x.x.25
> > > >
> > > > It's along the same lines as the question you posed, but a little
> more
> > > > challenging since you only want those 4 addresses to pass
> through.....
> > =)
> > >
> > >
> > >
> > > ___________________________________
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>
>
>
>
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