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Re: Make a DHCP server using Fedora - Help



Antonio and others, I'm writing the stuff below off the top of my head --- 
please feel free to correct me if necessarry, I may have slipped here or 
there... ;-)

On Sunday 16 November 2008 20:52, Antonio Olivares wrote:
> I changed DHCPDARG=eth0 as was suggested, but not working.

I missed this part. Where did you put this?

> The original machine gets its ip from a central server and then I want to
> use it as a server for several machines in my classroom.
>
> It connects to 10.154.19.210 which is its address in the "BIG" network.  it
> gets DNS 10.154.16.130, 10.128.0.4 and gateway 10.154.19.1

Ok. I suggest the following setup. Get the cable coming from the "big" network 
and plug it into your eth0. Then, take a small hub/switch/router/whatever and 
connect your classroom computers to it (I guess this is already set up). Make 
sure that *no* cable connects your hub to the "big" network. Instead, connect 
the hub to the eth1 of your server. Your server should be the only link 
between the big network and classroom network.

Leave eth0 configuration for later.

Configure eth1 device to have a *static* (manually assigned) IP address, 
say, 192.168.0.1 with netmask 255.255.255.0 and bring it up. Do this using 
"system-config-network" interface and running "service network restart". Make 
sure there is nothing related to NetworkManager active in the setup.

Next, configure dhcpd.conf in the following (most elementary) way, for the 
time being:

###########################
default-lease-time 21600; #600
max-lease-time 43200;     #7200
ddns-update-style none;
authoritative;

subnet 10.154.19.0 netmask 255.255.255.0 {
} # this means don't do anything with the big network

subnet 192.168.0.0 netmask 255.255.255.0 {
option routers 192.168.0.1  # your server is the router for classroom
option subnet-mask 255.255.255.0  # the mask given to classroom
option domain-name-servers 10.154.16.130, 10.128.0.4; # dns servers
range 192.168.0.2 192.168.0.254  # the pool of addresses for classroom
}
###########################

Save, do a "service dhcpd restart" (it should say OK), then
"tail -f /var/log/messages" and watch what is going on. Restart the clients 
(one by one if you wish to examine /var/log/messages after each client, 
otherwise you may restart them all simultaneously :-)...).

[[ N.B. I suppose you have configured the clients to use dhcp and not have 
anything statically assigned... ]]

What should be going on is that the clients in the classroom ask for IP 
configuration (dhcp request), then dhcpd replies with the data above (dhcp 
offer) and then each client accepts this offer. If all goes well, up to this 
point each client should have a 192.168.0.* IP assigned dynamically, and be 
able to ping any other client with such address, as well as the server, 
192.168.0.1. If this doesn't happen, tell us what does happen.

If all is well, up to now you have a working dhcpd configuration and each 
client has an IP assigned. In /var/lib/dhcp/dhcpd.leases you have a list 
stating which client (distinguished by its MAC address) has which IP assigned 
to it. The leases file may have some stale/old/obsolete information (because 
you have been playing with dhcpd before) --- ignore it, look at the bottom of 
the file, where fresh information is stored.

The next step is to configure NAT (network address translation) on your 
server's firewall, in order to allow the clients to access the "big" network 
using your server as a router. But this is a different problem --- first make 
sure the above configuration works, and then we'll go to the NAT 
configuration after that. One step at a time. ;-)

HTH, :-)
Marko


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