Problem with 2 ethernet card with different subnet mask

Hi,

I’ve two groups of PC with two different subnet mask. Between this two groups I’ve installed a new PC (with OpenSuse) with two ethernet card with the two different subnet mask. With windows I’d have seen this PC in every group, but with openSuse it seems to me that it is impossible. In fact I see that in the start menu appears “Using Eth1” or “Using eth2”. Is it possible to use both ethernet together?

Thank so much.

There is nothing wrong per se with having different masks for different interfaces. And in fact different interfaces must belong to different subnets. How about posting some actual addresses so that we can work out what you really mean? If they are private addresses, you are not exposing yourself to any danger.

Hi, Thank you… I try.

I’ve one subnet like 255.255.255.0 with some PC an the other is 255.255.192.0 with some other. I want to instal one PC which can be seen from both group. So I put the two eth card with two IP and the two subnet. But, as I told, it seems to me that se use only one card for time so this PC can’t be seen from one of the two subnet. Is it clear for you? Thank in advance.

ken_yap asked not only for the acutual masks you are using, but also for the actual addreses. You will have a problem when the two ranges overlap. We can only check that, when we get the full information. Don’t be so shy :shame:

ah!:wink:
There is so many PC and I don’t know the ip adress of everyone. But if you tell me what means “range overlap” I could try to verify in each PC! Are you so kind? Many thank.

I mean the two addresses you are using on the PC where we are talking about. The one with the two NICs.

And please give them with the mask that belongs to each, so we do not have to guess which goes with which.

1:
ip: 192.168.0.210
sb: 255.255.255.0

2:
ip: 192.168.0.211
sb: 255.255.192.0

Thank

This can not work, not even with that strange (what is the sense in that?) second netmask (which just creates a bigger range for the second card than for the first one, but still overlapping so how is that supposed to work?).

Which brings us back to:

Right. Another notation of the same networks is:
#1: 192.168.0.0/24
#2: 192.168.0.0/18
This means that:
. network #1 has the addresses ranging from 192.168.0.0 - 192.168.0.255;
. network #2 has the addresses ranging from 192.168.0.0 - 192.168.63.255.
and these overlap! #1 is a subnet of #2. Even both IP addresses you use do belong to both networks. How can any router even decide where to go for these addresses?

Sorry, are you so kind to tell me what subnets have I to write and the two range of the PC? Thank You.

For the record (and for people who don’t want to calculate this themselves):

IP Calculator / IP Subnetting - 192.168.0.0/255.255.255.0

IP Calculator / IP Subnetting - 192.168.0.0/255.255.192.0

One of many free IP/Netmask/Subnet/-calulators on the net.

I think you are clairvoyant and saw me using a Texas Intstruments Programmer II and even some pen/paper to make the calculations lol!

Thanks for the links.

You actually HAVE a calculator and pen/paper?

stares at that abacus on the table in jealousy

Yes, yes. Look at my age and you will understand why I have a museum here.

On Fri September 4 2009 05:16 am, digitaldavid wrote:

>
> Sorry, are you so kind to tell me what subnets have I to write and the
> two range of the PC? Thank You.
>
>
digitaldavid;
It depends a bit on the number of IP’s you need. This example will give you
two distinct subnets of about 250 available IP’s each.


192.168.0.0/24 (i.e. mask 255.255.255.0)
192.168.1.0/24 (i.e. mask 255.255.255.0)

There are actually 255 IP’s in each range, but a couple are reserved for
special use.


P. V.
“We’re all in this together, I’m pulling for you.” Red Green

If you are building some home LANs and have a choice in the subnets (as opposed to taking what the modem/router mfr gives you), then I would also suggest varying the third octet from the common 0 or 1.

Reason is one day you may discover VPNs and say decide you want to connect to your relative’s LAN via VPN, and oops, they have taken the same range as you. There’s no need to start at 0 when there are 256 choices.

For the same reason, I also recommend that work LANs use some uncommonly picked subnets, like a subnet of 172.16.0.0/12 or 10.0.0.0/8 so that they don’t accidentally clash with home LANs that have a consumer modem/router to the Internet. This actually happened at one place I worked at. By the time I came onto the scene there were too many machines in 192.168.0.0/24 and I had to tell a handful of VPN users to vary their home LAN subnet to use the VPN.

On Fri September 4 2009 06:06 pm, ken yap wrote:

>
> If you are building some home LANs and have a choice in the subnets (as
> opposed to taking what the modem/router mfr gives you), then I would
> also suggest varying the third octet from the common 0 or 1.
>
> Reason is one day you may discover VPNs and say decide you want to
> connect to your relative’s LAN via VPN, and oops, they have taken the
> same range as you. There’s no need to start at 0 when there are 256
> choices.
>
> For the same reason, I also recommend that work LANs use some
> uncommonly picked subnets, like a subnet of 172.16.0.0/12 or 10.0.0.0/8
> so that they don’t accidentally clash with home LANs that have a
> consumer modem/router to the Internet. This actually happened at one
> place I worked at. By the time I came onto the scene there were too many
> machines in 192.168.0.0/24 and I had to tell a handful of VPN users to
> vary their home LAN subnet to use the VPN.
>
ken;

Good point! Many routers allow you to configure the IP range although they
often default to either 192.168.0 or 192.168.1. There is no reason that my
examples could not have been 192.168.123.0/24 and 192.168.217.0/24 (or any
other distinct third octet).

And as a correction to my earlier post, there are actually 256, not 255, IP’s
in each of the subnets I gave; 0 through 255. However as stated earlier a
couple are reserved.

P. V.
“We’re all in this together, I’m pulling for you.” Red Green

THANK all!! Can yo tel me one exemple of two - non continuous subnet mask to evitate that one rappresents only a bigger range of the second? Thank you.

Sorry, I do not quite understand what you mean here.

The information provided above by different people must be enough for you to get the picture. When you need two bigger subnets (having place for more than 254 systems) you can use the 10.0.0.0/8 private network. Make subnets like 10.1.0.0/16 and 10.2.0.0/16. Or 10.1.0.0/16 for a big one and 10.2.1.0/24 for a small one (the last leaves you place for more then 200 of those small ones like 10.2.2.024, 10.2.3.0/24, …).

It is like a piece of cake. You can split it in two halves. And you can split one of those halves in say 8 pieces. But you can not eat any piece of a cake and have a part of that piece being eaten by another guy.
(This is one of the better metaphores I ever invented rotfl! , makes me hungry)

Ja, lucky I ate before I saw your post. lol!

Coming up soon: why VPN is like chocolate. Ooh, I feel hungry again. rotfl!