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if instead of 0.0.0.0 netmask is 255.0.0.0, I can't go on internet. That doesn't make sense...

Hello

1)
I'm running W2k on PC called A ( it's not really named A, but for the
sake of argument ...) and if my routing table has

( destionation )0.0.0.0   ( netmask )255.0.0.0
( gateway )192.168.2.1

instead of

( destionation )0.0.0.0    (netmask)0.0.0.0    (gateway)192.168.2.1

then I can't get on internet. I know address 0.0.0.0 basically means
"send the packet on internet", but why needs netmask be 0.0.0.0?
Afterall, all that netmask 255.0.0.0 should tell  A is that
destination address is not on the same network as A is, and thus
should send it to default gateway. But it doesn't, or gateway doesn't
send it forward. Why?

2)
Also, why does command

route add  64.283.183.103   mask 255.0.0.0  192.168.2.1

give me an error saying netmask is not valid?
Afterall, 64.283.183.103  is  class A address  ( I realize we can
subnet a range of class A addresses, but still that doesn't make
255.0.0.0 wrong )!


thank you

0
beginner16
8/6/2007 8:11:18 PM
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On Mon, 06 Aug 2007 13:11:18 -0700, beginner16 wrote:

> Hello
> 
> 1)
> I'm running W2k on PC called A ( it's not really named A, but for the
> sake of argument ...) and if my routing table has
> 
> ( destionation )0.0.0.0   ( netmask )255.0.0.0 ( gateway )192.168.2.1
> 
> instead of
> 
> ( destionation )0.0.0.0    (netmask)0.0.0.0    (gateway)192.168.2.1
> 
> then I can't get on internet. I know address 0.0.0.0 basically means
> "send the packet on internet", but why needs netmask be 0.0.0.0?
> Afterall, all that netmask 255.0.0.0 should tell  A is that destination
> address is not on the same network as A is, and thus should send it to
> default gateway. But it doesn't, or gateway doesn't send it forward.
> Why?

A route to 0.0.0.0/255.0.0.0 (or more succinctly 0.0.0.0/8) will only 
match ip addresses 0.0.0.1 to 0.255.255.255 (ok, the last one is a 
broadcast address). So you will be able to connect to ip addresses in 
that range, which will not help you much.

OTOH, 0.0.0.0/0 means ip addresses 0.0.0.1 through 255.255.255.255, or 
more precisely, the complete ipv4 address space.

> 
> 2)
> Also, why does command
> 
> route add  64.283.183.103   mask 255.0.0.0  192.168.2.1
> 
> give me an error saying netmask is not valid? Afterall, 64.283.183.103 
> is  class A address  ( I realize we can subnet a range of class A
> addresses, but still that doesn't make 255.0.0.0 wrong )!

First. Stop thinking in classful addresses. There used to be a class A. 
Nowadays, the IP space is carved up like it is needed, not how it was 
thought up to be divided in classes years ago. Your comment on subnetting 
made sense 15 years ago, but today classes just don't exist.

Other than that it looks just fine, so I would write that off as a 
Windows thingy.

HTH,
M4

0
Martijn
8/6/2007 11:25:45 PM
On Aug 6, 4:25 pm, Martijn Lievaart <m...@rtij.nl.invlalid> wrote:
> On Mon, 06 Aug 2007 13:11:18 -0700, beginner16 wrote:

> > 2)
> > Also, why does command
>
> > route add  64.283.183.103   mask 255.0.0.0  192.168.2.1
>
> > give me an error saying netmask is not valid? Afterall, 64.283.183.103
> > is  class A address  ( I realize we can subnet a range of class A
> > addresses, but still that doesn't make 255.0.0.0 wrong )!

> Other than that it looks just fine, so I would write that off as a
> Windows thingy.

Not a Windows thingy.  All of the bits not covered by the
mask must be 0.  It's a sanity check since only the bits
where the mask is non-zero are significant for a route.

Anoop

0
anoop
8/7/2007 12:01:50 AM
On Tue, 07 Aug 2007 00:01:50 +0000, anoop wrote:

> Not a Windows thingy.  All of the bits not covered by the mask must be
> 0.  It's a sanity check since only the bits where the mask is non-zero
> are significant for a route.

Can't believe I mist that. Thanks.

M4
0
Martijn
8/7/2007 5:57:51 AM
On Aug 7, 2:01 am, anoop <ghanw...@gmail.com> wrote:
> On Aug 6, 4:25 pm, Martijn Lievaart <m...@rtij.nl.invlalid> wrote:
>
> > On Mon, 06 Aug 2007 13:11:18 -0700, beginner16 wrote:
> > > 2)
> > > Also, why does command
>
> > > route add  64.283.183.103   mask 255.0.0.0  192.168.2.1
>
> > > give me an error saying netmask is not valid? Afterall, 64.283.183.103
> > > is  class A address  ( I realize we can subnet a range of class A
> > > addresses, but still that doesn't make 255.0.0.0 wrong )!
> > Other than that it looks just fine, so I would write that off as a
> > Windows thingy.
>
> Not a Windows thingy.  All of the bits not covered by the
> mask must be 0.  It's a sanity check since only the bits
> where the mask is non-zero are significant for a route.
>
> Anoop

I don't think I understand what you are trying to say.

>  All of the bits not covered by the mask must be 0.

Why?! I though one can specify a direct route also!

0
beginner16
8/8/2007 8:27:26 PM
On Wed, 08 Aug 2007 13:27:26 -0700, beginner16 wrote:

> On Aug 7, 2:01 am, anoop <ghanw...@gmail.com> wrote:
>> On Aug 6, 4:25 pm, Martijn Lievaart <m...@rtij.nl.invlalid> wrote:
>>
>> > On Mon, 06 Aug 2007 13:11:18 -0700, beginner16 wrote:
>> > > 2)
>> > > Also, why does command
>>
>> > > route add  64.283.183.103   mask 255.0.0.0  192.168.2.1
>>
>> > > give me an error saying netmask is not valid? Afterall,
>> > > 64.283.183.103 is  class A address  ( I realize we can subnet a
>> > > range of class A addresses, but still that doesn't make 255.0.0.0
>> > > wrong )!
>> > Other than that it looks just fine, so I would write that off as a
>> > Windows thingy.
>>
>> Not a Windows thingy.  All of the bits not covered by the mask must be
>> 0.  It's a sanity check since only the bits where the mask is non-zero
>> are significant for a route.
>>
>> Anoop
> 
> I don't think I understand what you are trying to say.
> 
>>  All of the bits not covered by the mask must be 0.
> 
> Why?! I though one can specify a direct route also!

Yes, that would be:

route add  64.283.183.103   mask 255.255.255.255  192.168.2.1

or to use the netmask you used:

route add  64.0.0.0   mask 255.0.0.0  192.168.2.1

To repeat, the bits that are zero in the netmask, must also be zero in 
the network address you are trying to route.

HTH,
M4
0
Martijn
8/8/2007 9:12:17 PM
In article <1186604846.768261.266170@d55g2000hsg.googlegroups.com>,
 beginner16 <kaja_love160@yahoo.com> wrote:

> On Aug 7, 2:01 am, anoop <ghanw...@gmail.com> wrote:
> > On Aug 6, 4:25 pm, Martijn Lievaart <m...@rtij.nl.invlalid> wrote:
> >
> > > On Mon, 06 Aug 2007 13:11:18 -0700, beginner16 wrote:
> > > > 2)
> > > > Also, why does command
> >
> > > > route add  64.283.183.103   mask 255.0.0.0  192.168.2.1
> >
> > > > give me an error saying netmask is not valid? Afterall, 64.283.183.103
> > > > is  class A address  ( I realize we can subnet a range of class A
> > > > addresses, but still that doesn't make 255.0.0.0 wrong )!
> > > Other than that it looks just fine, so I would write that off as a
> > > Windows thingy.
> >
> > Not a Windows thingy.  All of the bits not covered by the
> > mask must be 0.  It's a sanity check since only the bits
> > where the mask is non-zero are significant for a route.
> >
> > Anoop
> 
> I don't think I understand what you are trying to say.
> 
> >  All of the bits not covered by the mask must be 0.
> 
> Why?! I though one can specify a direct route also!

You need to understand the general algorithm for searching the routing 
table and how network masks fit into this.

To determine if an entry {network, mask} in the routing table is a 
candidate for the destination you're trying to send to, you perform the 
following test:

if ((destination & mask) == network)

In the case you tried, this test can NEVER be true, because the zero 
bits in the mask will turn all the corresponding bits in the destination 
to 0, so they can't match the .283.183.103 part of the routing table 
entry.  The "route add" command recognizes when you're trying to create 
such a nonsensical entry and rejects it.

-- 
Barry Margolin, barmar@alum.mit.edu
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 ***
0
Barry
8/9/2007 2:55:04 AM
Reply:

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