DHCPD and Assigning Subnets to Different Interfaces

metallica1973 · 01-20-2008, 12:42 PM

How would I assign a range of ip's from differents subnets on different interface cards. Example:

eth0 - 192.168.5.0/27 and eth1 - 192.168.4.0/27 using dhcpd

help

blackhole54 · 01-20-2008, 03:02 PM

/etc/dhcpd.conf doesn't explicitly reference interfaces (eth0, etc), just subnets. (I am assuming you already have your interfaces configured properly.)

Here is a dhcpd.conf I use with two subnets, each on its own card. (I've obfuscated the exact addresses with Xs.)

Code:

ddns-update-style ad-hoc

subnet 192.168.2.0 netmask 255.255.255.0 {
    range 192.168.2.XX 192.168.2.XX;
    default-lease-time 7200;
    max-lease-time 21600;
    option routers 192.168.2.XXX;
    option ip-forwarding off;
    option broadcast-address 192.168.2.255;
    option subnet-mask 255.255.255.0;
    option domain-name-servers 65.XX.XX.XX, 65.XX.XX.XX;
  }

subnet 192.168.1.0 netmask 255.255.255.0 {
    range 192.168.1.XX 192.168.1.XX;
    min-secs 3;
    default-lease-time 7200;
    max-lease-time 21600;
    option routers 192.168.1.X;
    option ip-forwarding off;
    option broadcast-address 192.168.1.255;
    option subnet-mask 255.255.255.0;
    option domain-name-servers 65.XX.XX.XX, 65.XX.XX.XX;
  }

I hope this helps.

finegan · 01-20-2008, 09:13 PM

2 conf files, two seperate dhcpd invokes, so:

dhcpd -cf /etc/dhcpd-network1 eth0
dhcpd -cf /etc/dhcpd-network2 eth1

Cheers,

Finegan

acid_kewpie · 01-21-2008, 08:00 AM

//mod note - code tag chat moved to new thread

you don't need two files, that's really not a great design to follow. the pool that is allocated from is the one upon which the dhcp request is heard, it's all implicit. similarily, if you use a dhcp relay in a router elsewhere in the netwrok that will forward requests to the server including the ip address of it's listening interface so that too knows which network toallocate from.

metallica1973 · 01-24-2008, 07:19 AM

PHP Code:



ddns-update-style ad-hoc 
 
subnet 192.168.2.0 netmask 255.255.255.0 { 
    range 192.168.2.XX 192.168.2.XX; 
    default-lease-time 7200; 
    max-lease-time 21600; 
    option routers 192.168.2.XXX; 
    option ip-forwarding off; 
    option broadcast-address 192.168.2.255; 
    option subnet-mask 255.255.255.0; 
    option domain-name-servers 65.XX.XX.XX, 65.XX.XX.XX; 
  } 
 
subnet 192.168.1.0 netmask 255.255.255.0 { 
    range 192.168.1.XX 192.168.1.XX; 
    min-secs 3; 
    default-lease-time 7200; 
    max-lease-time 21600; 
    option routers 192.168.1.X; 
    option ip-forwarding off; 
    option broadcast-address 192.168.1.255; 
    option subnet-mask 255.255.255.0; 
    option domain-name-servers 65.XX.XX.XX, 65.XX.XX.XX; 
  }

that I understand but

Quote:

Here is a dhcpd.conf I use with two subnets, each on its own card.

So just adding these different subnets in dhcpd.conf should work, so I dont need to:

PHP Code:



dhcpd -cf /etc/dhcpd-network1 eth0 
dhcpd -cf /etc/dhcpd-network2 eth1

correct? I am a bit confused. thanks

farslayer · 01-24-2008, 10:47 AM

One dhcpd server,
one dhcpd config file
dhcp relay agent - http://linux.die.net/man/8/dhcrelay

relaying can be done by a workstation, server, router, etc.. the relay agent will be located on any subnets that do not have a local dhcp server on them.

I used ONE dhcp server to hand out addressing to 20 subnets and used the ip helper-address command in the cisco routers to forward all dhcp requests to my dhcp server. It worked flawlessly.

acid_kewpie · 01-24-2008, 11:09 AM

can't find a nice ascii block diagram for it, but check http://www.cisco.com/en/US/tech/tk64...80094b50.shtml

you can see a nice debug of a bootp relay packet there, and in there is the IP address of the cisco router which would have the ip helper-address on it, and so when the dhcp server recieves it it has a reference point to use to know what subnet is relevant.

blackhole54 · 01-24-2008, 11:50 PM

Quote:

Originally Posted by metallica1973

So just adding these different subnets in dhcpd.conf should work, so I dont need to:

Code:

dhcpd -cf /etc/dhcpd-network1 eth0
dhcpd -cf /etc/dhcpd-network2 eth1

correct? I am a bit confused. thanks (Empahsis added)

Correct. If I understand your situation, you just need one conf file similar to what I posted (adjust as needed) and one instance of dhcpd. dchpd knows the configuration of each of your NICs and will assign addresses from the proper subnet. As best as I can figure out, the rest of this conversation about relaying, etc. while it might be correct, is beyond what I take to be your fairly basic needs.

EDIT: Just to be clear, my single instance of dhcpd is invoked from within my distoro's /etc/init.d/dhcpd script, but no parameters are supplied to dhcpd. So it is looking at all (in my case, two) NICs.

metallica1973 · 01-25-2008, 05:22 AM

I am going to make another post because I screwed things up last. Many thanks