custom subnet mask

[Steve]

We're going to be implementing a subnet mask of 255.255.254.0 using IP range
192.168.0.1 - 192.168.1.254 (we need approx 280 IPs) - I've done a simple
test with a few PCs and all seems to be ok.

I've got a general question, just out of curiousity:
Let's assume no DHCP for the sake of this question.

Now, using 255.255.254.0 gives me approx 512 IPs, so two "ranges" of IPs.

I was setting up a couple of PCs with 192.168.1.x IPs, and it struck me, why
does that work with 192.168.0.x ? I mean, as far as the PC with a 192.168.1.x
is concerned, it could work with either 192.168.0.x or 192.168.2.x. Is it
because it is "set" as soon as any PC shows up on the LAN with either a
192.168.0.x or a 192.168.2.x ?

Or is like this:
A PC with a 192.168.1.x IP could communicate with both a PC with a 192.168.0.x
and with a PC with a 192.168.2.x IP, but the 192.168.0.x could communicate with
only with the 192.168.1.x PC. Is that correct?

Like I said, just curious.

Thanks

 

[Dave]

no, the range is set by combining the machine's ip address with the mask.
so with your 255.255.254.0 mask the groups you can use are:

192.168.0.0-192.168.1.255
192.168.2.0-192.168.3.255
192.168.4.0-192.168.5.255
192.168.6.0-192.168.7.255

all machines that need to talk to each other must be in the same range of
addresses above.

 

[Steve]

Ok, then a 192.168.1.x machine can't communicate with a 192.168.2.x machine.
I just tried that, and indeed, it didn't work.
Thanks

 

[Herb Martin]

Ok, then a 192.168.1.x machine can't communicate with a 192.168.2.x machine.
I just tried that, and indeed, it didn't work.
Thanks

Not without a router.

A 2.x can communitcate with 3.x without the router though.

If these machines use the network heavily you may have
a bandwidth problem and introducing a router and more
subnets might be a useful consideration.

 

[Steve]

Possible network congestion point well taken, we'll have to see how congested
things get. I'm sure we'll never get over 300 clients (probably 280 max), and
30 of those will be printers, switches.

Thanks.

 

[Herb Martin]

What kind of switches?

If the switches are router-switches (layer 3) or
have VLAN capability, you should likely make
separate subnets anyway.

If you don't then a BROADCAST must be sent to
EVER SEGMENT/LEG of every switch.

--
Herb Martin

Possible network congestion point well taken, we'll have to see how congested
things get. I'm sure we'll never get over 300 clients (probably 280 max), and
30 of those will be printers, switches.

Thanks.