Passing out nore than 254 IPs to a network ?

michaelsanford · 05-11-2005, 10:33 AM

I, like thousands of other administrators I'm sure, wants to serve out more than 254 IP addresses to a set of computers. I've not found any specific information on this, so I will assume that this is the solution and hope someone corrects me.

Do I just set up IP Aliasing on my single physical interface and alias it to various network names with corresponding entries in dhcpd.conf, like so?
wlan0 10.0.0.0
wlan0:1 10.0.1.0
wlan0:2 10.0.2.0

If that is the case, how does a connecting node know to join a particular network? Does dhcp realise that all the addresses in 10.0.0.0 are leased out and start leasing from 10.0.1.0 (somehow I think not)?

Also, for routing purposes, since this is a wireless network with a single AP (actually, multiple APs but the extra ones are acting as repeaters), how do I deal with the extra network addresses? Presumably if the default gateway is set to 10.0.x.1 (the Linux router) in each dhcp range it won't matter which network x represents.

EDIT I've received a partial answer to my question (part that I didn't ask) as to the dhcpd error message with multiple networks on a single interface. I still wonder about how IPs are passed out to clients though. http://www.linuxquestions.org/questi...hared+networks

fr_laz · 05-11-2005, 12:06 PM

Hi,

A subnet has 254 IPs available when its mask is 255.255.255.0
Why don't you configure your interface WLAN0 and dhcpd so that the mask becomes 255.255.0.0
Thus you'll have 256*254 IPs available...

michaelsanford · 05-11-2005, 12:14 PM

Like:

Code:

subnet 10.0.0.0 netmask 255.255.0.0 {
        option routers 10.0.0.1;
        option domain-name-servers 206.47.244.12, 206.47.244.42;
        option ip-forwarding on;
        range 10.0.0.2 10.0.255.255;
}

?

fr_laz · 05-11-2005, 12:28 PM

Re,

yes that's it.

range 10.0.0.2 10.0.255.255; should be range 10.0.0.2 10.0.255.254;

you've got to change your wlan0 config also : if it still has the 255.255.255.0 mask it won't be able to communicate with devices in the 10.0.x.0 (x != 0) subnets.

what's the option ip-forwarding on; ? I never saw it...

If you've got some machines with static IP, don't forget to change their network mask and to forbid the dhcp server to give their IP to another host.

michaelsanford · 05-11-2005, 01:55 PM

Woops quite right on the network range! (I did know that

)

As for forbidding static IP address duplication, is that as simple as adding a host {} directive inside the subnet {} (which is how I currently do static IP addressing).

I think the reason I went off on this multi-network tangent is because I tried this method initially, before I had any conception of subnetting and naturally it failed.

Thanks for the help !

EDIT: Actually, what I was planning on doing for static IP addressing is to reserve a range of hosts (say 10.0.254.0) for static addressing only, so I could exclude that from the dynamic range...

Ougle · 05-11-2005, 02:02 PM

I think this helps me with a curiosity I had today.

I didn't know about the subnet mask, what values it can be other than 255.255.255.0 and why have it.

So a subnet mask can be:
255.255.255.0
255.255.0.0
and possibly 255.0.0.0 ?

And it sets the range of the network the computer is on?
I.e. the 255 parts of the ip will be the same to designate the network, and the 0 parts of the ip will differ to make each computer have a unique ip?

michaelsanford · 05-11-2005, 02:08 PM

Essentially, yes, though it's a little more complicated than that, check out this reply (also from fr_laz) to another thread of mine, it explains netmasks well:
http://www.linuxquestions.org/questi...26#post1636626

EDIT However subnetting is much more complex than that, because you can have netmasks other than 255 or 0 and they have special meanings:
http://yolinux.com/TUTORIALS/LinuxTu...g.html#SUBNETS