interesting subnet question

If you have two machines with the following setings,


[ Machine 1 ] IP: 192.168.0.1, Subnet: 255.255.255.0
[ Machine 2 ] IP: 192.168.0.2, Subnet: 255.255.255.252

will the M1 be able to ping M2? What about the other way round? The subnet
of M2 allows it to talk to IP addresses 192.168.0.1-192.168.0.3, right?


What do the RFCs say about this?


cheers,

C3

On Sun, 22 Feb 2004 22:41:20 +1100, C3 wrote:
> If you have two machines with the following setings,
>
>
> [ Machine 1 ] IP: 192.168.0.1, Subnet: 255.255.255.0
> [ Machine 2 ] IP: 192.168.0.2, Subnet: 255.255.255.252
>
> will the M1 be able to ping M2? What about the other way round? The subnet
> of M2 allows it to talk to IP addresses 192.168.0.1-192.168.0.3, right?

The subnet of M2 defines a rather restricted localnet, essentially
where it will send broadcast traffic. A subnet mask is not an IP
filter - there's nothing there to prevent either from pinging the
other unless you've got network gear enforcing a "correct" subnet
mask in which case one of the boxes simply won't be connected.

> What do the RFCs say about this?

About the difference between a subnet mask and an IP filter? I
can't imagine anyone thinking they'd need an RFC for that. But
feel free to browse http://www.ietf.org/ yourself.

Bjørn
--
Bjørn Tore Sund "When in fear, and when in doubt;
(E-Mail Removed) Run in circles, scream and shout!"
Interaction! - Anonymous
http://www.interaction.worldcon.org.uk/

I have found that when I set a client machine up with a restrictive subnet
mask (.252), it will not directly contact other local machines. Instead, it
will forward the packets to the default router and try to get them routed
that way.

Under Windows 2000 at least, the subnet mask seems to indeed prevent
machines on the same segment talking to each other. I'm trying to figure out
how this works exactly.


cheers,

C3

So anyway, it was like, 02:05 CET Feb 23 2004, you know? Oh, and, yeah,
C3 was all like, "Dude,

> I have found that when I set a client machine up with a restrictive
> subnet mask (.252), it will not directly contact other local
> machines. Instead, it will forward the packets to the default router
> and try to get them routed that way.

Yes, this /is/ the expected result of setting a subnet mask. In fact,
it's pretty much the reason why they exist in the first place, to
define which addresses can be connected to directly and which needs
the assistance of a router to be reached.

> Under Windows 2000 at least, the subnet mask seems to indeed prevent
> machines on the same segment talking to each other. I'm trying to
> figure out how this works exactly.

Any basic class in networking would teach you all you need to know
here. Or a book titled "Networking for dummies", I expect.

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