Subnetworking: Yes or No? If yes when?

Dear Group
Given the subject line I am obviously new to networking and so green it
could be spring!

I did some HowTo reading, but never found an answer to my very basic
question. Do I have to subnetwork or not? If yes, under what conditions do I
have to subnetwork? Here follows a description of my network:

The network consists of 2 Lin boxes, 3 dual boot Lin/ W2k systems and a
802.11 router that connects to DSL.

One Lin box, the file server, contains three interfaces: wlan0, eth0, eth1
and is connected wirelessly to the 802.11 router. 2 Lin/Win systems connect
to the interfaces eth0 and eth1 respectively. This box runs the dhcpd (on
eth0 and eth1), named and smb server.

The 3rd Lin/Win system connects to the 802.11 router with a wire. The 802.11
router is in gateway mode and runs a dhcpd server also.

The 2nd Lin box connects to the 802.11 router with a wire as well.

Right now I am running a subnet on the router and another subnet on the file
server on eth0 and eth1. However, I cannot get the my Lin/Win systems to
communicate with the gateway. So I decided to start from scratch and get
some basics straightened out.

Do I have to subnetwork given the above setup? If yes, how? Does each
interface on the file server have to be subnetworked?

Thank you very much for your help in advance!

With kind regards
Beat Naef

Beat Naef wrote:
> Dear Group
.......zip

Dear Beat,
No, you don't have to make a lot of different subnets. If you want your
win and linux boxes to communicate with each other it's easier to have
them all on one network. (Tip: _only_ one dhcp-server/network)

But the time will come where you would like :-)
some more security, a firewall, a separate wlan subnet, etc. Thats the
first time where you should think of splitting up networks...

Cheers,
Monzai

If you have a lot of web-frontends to manage your network and configure
your services sooner or later you will need a tool like Monzai!
Since it is so hard to describe Monzai, please have a look at
http://www.monzai.com/

On Tue, 23 Sep 2003 16:21:50 GMT, Beat Naef <res0wt83@verizon.net> wrote:
> The network consists of 2 Lin boxes, 3 dual boot Lin/ W2k systems and a
> 802.11 router that connects to DSL.
>
> One Lin box, the file server, contains three interfaces: wlan0, eth0, eth1
> and is connected wirelessly to the 802.11 router. 2 Lin/Win systems connect
> to the interfaces eth0 and eth1 respectively. This box runs the dhcpd (on
> eth0 and eth1), named and smb server.

One problem is that your gateway probably only knows about the subnet
directly connected to it and knows nothing about how to route to your
other subnets. So for those other subnets to access your gateway
(actually so the gateway knows where to return packets) you either need to
masquerade the other subnets, or have them be subsets of your main subnet,
using proxy_arp. Example of my setup:

Gateway 192.168.1.1 192.168.1.0/255.255.255.0
|
|--printserver 192.168.1.200 192.168.1.0/255.255.255.0
|
eth0 192.168.1.2 192.168.1.0/255.255.255.0 proxy_arp enabled
default gw 192.168.1.1
eth1 192.168.1.241 192.168.1.240/255.255.255.248
|
WAP 192.168.1.246 192.168.1.240/255.255.255.248


wlan0 192.168.1.245 192.168.1.240/255.255.255.248
default gw 192.168.1.241

Note that since proxy_arp is enabled on eth0, it answers arp requests for
IPs on eth1. So the Gateway or printerserver can find my wireless laptop
as though they were local (with arp broadcasting) instead of needing a
gateway to find the smaller subnet (ie, the small subnet is within and
becomes part of the main subnet).

Proxy arp for eth0 is enabled by:

echo 1 > /proc/sys/net/ipv4/conf/eth0/proxy_arp

I have not tried 3-way proxy arp, but you could try:

wlan0 some_ip netmask 255.255.255.0
default gw gateway_ip
eth0 some_ip netmask 255.255.255.255 broadcast (same as IP)
host route to remote IP on eth0
eth1 some_ip netmask 255.255.255.255 broadcast (same as IP)
host route to remote IP on eth1

Then enable proxy_arp for wlan0, eth0 and eth1

On the boxes connected to eth0 and eth1 use normal 255.255.255.0 netmask
and gateway to respective Linux eth0 or eth1 IP.

The IPs for Linux interfaces and the 2 boxes connected to it should be
outside of dhcp range assigned by main gateway (wireless router).

--
David Efflandt - All spam ignored http://www.de-srv.com/
http://www.autox.chicago.il.us/ http://www.berniesfloral.net/
http://cgi-help.virtualave.net/ http://hammer.prohosting.com/~cgi-wiz/

"Beat Naef" <res0wt83@verizon.net> writes:

> I did some HowTo reading, but never found an answer to my very basic
> question. Do I have to subnetwork or not? If yes, under what conditions do I
> have to subnetwork? Here follows a description of my network:

In general, on a small network, the only reason you may need to
subnetwork is if you have a computer or computers that need to be
administratively separated from the rest of your network. I.e., maybe
you want to add more protection to your payroll database box, so you put
it on a separate subnet, separated with a filtering router.

There is really no other good reason to subnet on a network that small.

--
Dave Carrigan
Seattle, WA, USA
dave@rudedog.org | http://www.rudedog.org/ | ICQ:161669680
UNIX-Apache-Perl-Linux-Firewalls-LDAP-C-C++-DNS-PalmOS-PostgreSQL-MySQL

THX to all that responded!

I have decided to first follow the suggestion that I should keep my
network as simple as possible (i.e. no subnetworking) and not to modify
my subnetworks to get them working together.

Therefore, I removed subnet 2 from Lin1/eth0 and subnet 3 from Lin1/eth1
and elevated subnet 1 between Lin1/wlan0 and the wireless router (to
which another machine is connected) to my overall network. The router
runs dhcpd. I turned off dhcpd on Lin1. Lin1/ wlan0 is getting BC, GW,
DNS and NW/mask information from the router now. So I have only 1 dhcpd
running on my network, namely on my router.

Now I would like that all the interfaces request network information
from the dhcpd that is running on my wireless router (i.e. Lin1/ wlan0,
Lin1/eth0 and Lin1/eth1). For the systems that are directly connected to
the router, that is not a problem. But how can I get eth0 and eth1 to
request network information across the box Lin1 to wlan0 and then to the
router? I tried to configure dhcprelay (I think that only works in
connection with subnets) and dhclient on Lin1. But I was not successful.

Any ideas how I can get all three interfaces on the Lin1 box requesting
network information from the same dhcpd?

With kind regards
Beat Naef


Dave Carrigan wrote:
> "Beat Naef" <res0wt83@verizon.net> writes:
>
>
>>I did some HowTo reading, but never found an answer to my very basic
>>question. Do I have to subnetwork or not? If yes, under what conditions do I
>>have to subnetwork? Here follows a description of my network:
>
>
> In general, on a small network, the only reason you may need to
> subnetwork is if you have a computer or computers that need to be
> administratively separated from the rest of your network. I.e., maybe
> you want to add more protection to your payroll database box, so you put
> it on a separate subnet, separated with a filtering router.
>
> There is really no other good reason to subnet on a network that small.
>