LAN IP addresses

Hi,

I am not a specialist on network, but I have a network on
192.168.0.0 / 255.255.255.0

I fear not to have enough IP addresses. I know, that the solution would
be to get another router and to get a second sub-network.

I just wonder if I change my LAN ( 192.168.0.x/255.255.255.0 ) to
192.168.x.x / 255.255.0.0
- Would it be possible to do that ?
- Would it get me all IP addresses like : 192.168.0.2 and 192.168.3.4
accessible on the same network ?
( ... that could solve my problem and five me more IP addresses ..... )

Thanks for your help

Am Fri, 05 Sep 2008 10:33:53 +0100 schrieb Steve:


> I just wonder if I change my LAN ( 192.168.0.x/255.255.255.0 ) to
> 192.168.x.x / 255.255.0.0
> - Would it be possible to do that ?
Sure why not.
But better you route between 2 /24 networks, otherwise you get the whole
/16 broadcasts to ever machine.

> - Would it get me all IP addresses like : 192.168.0.2 and 192.168.3.4
> accessible on the same network ?

Yes, but it's better to route that.

> ( ... that could solve my problem and five me more IP addresses ..... )
>
> Thanks for your help

My suggestions for you is, that you set up you networks as /24 and set the
route via the right interface, so you still take control between the
subnets and you don't have so much sensless traffic like broadcasts from
windows hosts.

cheers

Burkhard Ott wrote:
> Am Fri, 05 Sep 2008 10:33:53 +0100 schrieb Steve:
>
>
>> I just wonder if I change my LAN ( 192.168.0.x/255.255.255.0 ) to
>> 192.168.x.x / 255.255.0.0
>> - Would it be possible to do that ?
> Sure why not.
> But better you route between 2 /24 networks, otherwise you get the whole
> /16 broadcasts to ever machine.
>
>> - Would it get me all IP addresses like : 192.168.0.2 and 192.168.3.4
>> accessible on the same network ?
>
> Yes, but it's better to route that.
>
>> ( ... that could solve my problem and five me more IP addresses ..... )
>>
>> Thanks for your help
>
> My suggestions for you is, that you set up you networks as /24 and set the
> route via the right interface, so you still take control between the
> subnets and you don't have so much sensless traffic like broadcasts from
> windows hosts.
>
> cheers


Hi,

thanks for your reply.

When you say " routing between 2* /24 network" do you mean using a NAT
? ( If not.. what do you mean AND How to do that ?? )
.. that will decrease useless Broadcast !?

Cheers,

Am Fri, 05 Sep 2008 11:13:51 +0100 schrieb Steve:
> Hi,
>
> thanks for your reply.
>
> When you say " routing between 2* /24 network" do you mean using a NAT
> ? ( If not.. what do you mean AND How to do that ?? )


Let's assume you have a router with 3 seperate interfaces.

if0 has 192.168.0.0/24
if1 has 192.168.1.0/24
if2 has 192.168.2.0/24

If you want traffic from 192.168.0.0/24 to 192.168.2.0/24 your packet
arrives if0, here you can have filter policies ot whatever and the packets
leve the machine on if2, thats ist.

> .. that will decrease useless Broadcast !?

If you have an broadcast message on if0 and the ip 1-254 get those
packets, nobody from if1 or if2.
On every interface you can filter,nat,snat or wheterever you want.


cheers

Burkhard Ott wrote:
> Am Fri, 05 Sep 2008 11:13:51 +0100 schrieb Steve:
>> Hi,
>>
>> thanks for your reply.
>>
>> When you say " routing between 2* /24 network" do you mean using a NAT
>> ? ( If not.. what do you mean AND How to do that ?? )
>
>
> Let's assume you have a router with 3 seperate interfaces.
>
> if0 has 192.168.0.0/24
> if1 has 192.168.1.0/24
> if2 has 192.168.2.0/24
>
> If you want traffic from 192.168.0.0/24 to 192.168.2.0/24 your packet
> arrives if0, here you can have filter policies ot whatever and the packets
> leve the machine on if2, thats ist.
>
>> .. that will decrease useless Broadcast !?
>
> If you have an broadcast message on if0 and the ip 1-254 get those
> packets, nobody from if1 or if2.
> On every interface you can filter,nat,snat or wheterever you want.
>
>
> cheers


Thank you

Steve wrote:

> Hi,
>
> I am not a specialist on network, but I have a network on
> 192.168.0.0 / 255.255.255.0
>
> I fear not to have enough IP addresses. I know, that the solution would
> be to get another router and to get a second sub-network.
>
> I just wonder if I change my LAN ( 192.168.0.x/255.255.255.0 ) to
> 192.168.x.x / 255.255.0.0
> - Would it be possible to do that ?
> - Would it get me all IP addresses like : 192.168.0.2 and 192.168.3.4
> accessible on the same network ?
> ( ... that could solve my problem and five me more IP addresses ..... )
>
> Thanks for your help

This is just a side note.

As Burkhard Ott recommends you should be routing traffic between smaller
subnets, except you have many machines wanting to talk to few ones.

IANA (http://www.iana.org) says there are 256 subnets with a maximum of
256-2 (one network base and one broadcast address) addresses each in the
192.168.x.y address space. Bigger subnets should use 172.16-31.x.y which
allows 16 subnets with a maximum of (256^2)-2 = 65534 addresses each. Or,
if even larger subnets are required, use 10.x.y.z which allows one huge
subnet of (256^3)-2 = 16777214 addresses.
This is a relict of the old times when there were no netmasks, but it is
still valid...

So if you intend to widen up your netmask you should also use appropriate
address space.

Felix

Felix Tiede wrote:
> IANA (http://www.iana.org) says there are 256 subnets with a maximum of
> 256-2 (one network base and one broadcast address) addresses each in the
> 192.168.x.y address space. Bigger subnets should use 172.16-31.x.y which
> allows 16 subnets with a maximum of (256^2)-2 = 65534 addresses each. Or,
> if even larger subnets are required, use 10.x.y.z which allows one huge
> subnet of (256^3)-2 = 16777214 addresses.
> This is a relict of the old times when there were no netmasks, but it is
> still valid...

No, its not valid anymore. The whole purpose of netmasks is to replace
the old class A, class B and class C concept.

>
> So if you intend to widen up your netmask you should also use appropriate
> address space.

Normally there shouldn't be any need to do so. You _do_ have an 64K
space available in the 192.168.x.y range.

That having said, we _did_ have some issues when we moved from a /24 to
a /23 netmask at work years ago. That must have been in 2001 IIRC.
We changed our netmask to join two adjacent formerly class C address
blocks -located in a public address range- into a single broadcast
domain. Some of our equipment didn't support that; most notably:
-- some -already old at that time- Tektronix X-terminals
-- a few -recent at that time- Dell network printers.
Those printers and X-terminals _did_ support the netmask concept
properly to divide a formerly class C network into smaller subnets,
but failed when moving the netmask in the other direction.


Regards,

Kees.

--
Kees Theunissen.

Hello,

Moe Trin a écrit :
>
> By the way, there is nothing sacred about the "zero" address, and some
> operating systems specifically do allow use of the "network" address
> as a _host_ address.

RFC 1812 states otherwise in § 4.2.2.11, 4.2.3.1, 5.3.5. If such an
address is used, it must be treated as a broadcast and cannot be used as
a host address. One exception is of course when using a /31 prefix on a
point-to-point link as defined in RFC 3021.

Moe Trin a écrit :
>
>>>By the way, there is nothing sacred about the "zero" address, and
>>>some operating systems specifically do allow use of the "network"
>>>address as a _host_ address.
>>
>>RFC 1812 states otherwise in § 4.2.2.11, 4.2.3.1, 5.3.5.
>
> Perhaps the word "sacred" is to strong. None the less with the advent
> of CIDR, the meaning of the "network" and "broadcast" address can not
> be known to outsiders,

Wasn't this true already with subnetting, even before CIDR ?

> But then, a lot of people misinterpret RFC1122 Section 3.2.1.3 on
> page 31 (third paragraph below (g)) as prohibiting a zero (or -1
> which they don't understand) in any host part.

Hey, I interpret this paragraph this way too ! :-o
I quote it for completeness :

IP addresses are not permitted to have the value 0 or -1 for
any of the <Host-number>, <Network-number>, or <Subnet-
number> fields (except in the special cases listed above).

To me it clearly means that the host number part of a unicast host
address cannot be 0. What I am reading wrong ?

>>If such an address is used, it must be treated as a broadcast and
>>cannot be used as a host address.
>
> The "network" address has not been used as a broadcast address for a
> long time - 4.2BSD was replaced by 4.3 a bit over twenty years ago.

Anyway at least one modern OS, Linux, still interprets it as an
alternate directed broadcast address.

Moe Trin a écrit :
> Pascal Hambourg wrote:
>>Moe Trin a écrit :
>>>
>>>But then, a lot of people misinterpret RFC1122 Section 3.2.1.3 on
>>>page 31 (third paragraph below (g)) as prohibiting a zero (or -1
>>>which they don't understand) in any host part.
>>
>>Hey, I interpret this paragraph this way too ! :-o
>>I quote it for completeness :
>>
>> IP addresses are not permitted to have the value 0 or -1 for
>> any of the <Host-number>, <Network-number>, or <Subnet-
>> number> fields (except in the special cases listed above).
>>
>>To me it clearly means that the host number part of a unicast host
>>address cannot be 0. What I am reading wrong ?
>
> What is the "host number part"?

It is the right-most part of the IP address which has the corresponding
bits in the netmask set to 0 ass assumed in the RFC. Isn't it what you
meant by "host part" ?

> Most people wrongly assume that this
> refers to the right-most octet only,

They're wrong. This is true only for /24.

> Oh, and you may also want to notice the "<Subnet-number>" mentioned
> above (also mentioned in RFC1812 and the various 'Assigned Numbers"
> RFCs like RFC1700), and then look at RFC3330. It was common with some
> operating systems that the lowest and highest _subnet_ were considered
> unusable.

I knew about this. Actually I tend to consider that the subnet number is
deprecated since the advent of CIDR. An IP address contains a prefix and
a host number. Whether the prefix is the result of subnetting does not
matter to me, and I believe it should not matter to any network
equipement either.