How to assign public ip's using dhcpd on mandrake

Posted on 2003-03-09
Medium Priority
Last Modified: 2010-03-18
I have a server running mandrake 8.2
my connection is a fiber optic connection from my local hydro company.
I get no email no service at all with this service its wide open to the world
with no blocked ports and no cap its a commercial service.

So i decided to start a wireless ISP with it i have knowledge of private networking
but not much on public networking.

I've been allocated public ip's from x.x.x.226 to 238
my system has two network cards eth0 has address x.x.x.226 which has the fiber connected
directly to it, then i have eth1 with address connected to a switch hub.

This is where i have (for now) one system connected directly to that switch and one wireless access
point connected to (I only have one client and one access point for now till i do test and have it working).

What i would like to do is use DHCP on the mandrake system to allocate my range of PUBLIC! ip address's to clients rather then dumb ass private ip's like 192.168.x.x

I've been seaching the net for weeks no about dhcp and i've even read the entire handbook on dhcp
and man i'm gettin frustrated, anything reffered to in the documents always reffers to private ip's

Can some help with this problem?

Thank you in advanced.
Question by:recsx
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Expert Comment

ID: 8099806
What you're trying to do is very difficult.  First problem is if you assign those IPs to machines behind your firewall, it will be confused because IPs that should be on the same subnet are on both sides of it.

The next challenge is that a client with one of your IPs (e.g. x.x.x.227) won't want to pass packets to a router with IP because that's a different subnet.

To get around those problems, you'll want to have x.x.x.226/29 show up inside your firewall.  The first thing that comes to mind is to setup another router that's a mirror-image of your existing one:

routerB would have eth1 with IP and be connected to your existing box.  Then assign its eth0 to be x.x.x.227 and be connected to your other clients (x.x.x.228, etc).  Set its default router to

The next part is to convince your current router to forward packets for .227 - .236 to routerB.  Since it thinks it's already on this subnet, you'll need to override its default routing table.  Add host specific routing entries for x.x.x.227 - .236 and speicfy as the gateway.

I'd be interested to hear if this works for you.

Author Comment

ID: 8099872
Huh! well i realy dont have to use as my router.

This server is not really suppling any real service to anything at the moment other then the system im using to reply to this forum.

If you have any sugestions on how to configure both nics from scratch to allo me to provide these public ip's i think this would be an easier approach, do you think not?


Author Comment

ID: 8099907
Huh! well i realy dont have to use as my router.

This server is not really suppling any real service to anything at the moment other then the system im using to reply to this forum.

If you have any sugestions on how to configure both nics from scratch to allo me to provide these public ip's i think this would be an easier approach, do you think not?

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Expert Comment

ID: 8100076
Normally, you have a subnet of IPs (perhaps a /30) dedicated to the network between two routers.  But I'm guessing you don't have that between you and your ISP.

The easiest way to use all your real IPs is to plug a hub (or switch) into your WAN connection and run your DHCP server on x.x.x.226.

Then packets from your customers go straight to the hydro company and don't even pass through your linux box.

Author Comment

ID: 8100109
Ok thats sounds like it would work
But would i be able to trake traffice and apply rules if i did it this way?

Expert Comment

ID: 8100162
No, you wouldn't be able to filter traffic (inbound or outbound), only sniff it.

My first (complex) suggestion was trying to come up with a way that would let you filter traffic.

If you can get another subnet (only needs to be a /30) that you can use for your WAN link.  And get them to add an entry to their routing table that says your box is the gateway to the other subnet (x.x.x.226/29).  Then you'd be able to setup a standard router.

Accepted Solution

colonytire earned 300 total points
ID: 8100319
It's not that dificult.  The problem is unless you have a class C range of Ip's you won't be able to split them up very well for use as an ISP.  Split your range to give you 2 subnets.  You only need 2 addresses for your link. One of te addresses wil be on your router, and the other on your server.  Next assign an IP ususlly the first available of the other subnet to your LAN interface.  Then configure your DHCP serevr to use the remaining IP's for assignment. You may have to play with the default routes to direct traffic depending on how you want to customize it and how you want your customers data to flow. Also make sure to put in the default routes for your network. By this I mean your LAN side should direct all traffic to the WAN interface card, and the WAN to direct traffic to the router as their defaults. I would also highly reccomend the use of a RADIUS server to help authenticate your users. This will work very well as I have done ths many times for an ISP I once worked for. He too is using this same structure for his Wirless customers.

Hope this helps

Author Comment

ID: 8100371
Little vague but ok i think i get the jist of it.

One more question?, when you say router do you mean like a cisco router of some sort?

I'm going to look at a used cisco router tomorow a 2600 series.

Do you think this will do the job?

Expert Comment

ID: 9077706
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