Hi All,

I have one DHCP Server and four networks. The four networks are 10.191.41.X/24
10.191.42. X/24, 10.191.43.X/24 and 10.191.44.X/24. My DHCP server is on 10.191.41.X network that need to supply IPs for all networks. How I need to configure the DHCP server? What is the IP I need to keep for my DHCP server? Those networks are I divided on my switch in one interface with Virtual IP. All the networks connected in a single interface in my switch. Please help me out this problem?

Thanks,
Srikanth

you have multiple interface on the server ? and bind each subnet on each interface ?

You need to configure 4 scopes on the server, one for each subnet. You then need to configure the L3switch or router you are using to get between the subnets to forward DHCP/BOOTP packets to the server.
On a Cisco switch you go into the Vlan interface where the ip address is and enable bootp helper with the address of the server. Do this for each subnet. It doesn't matter what IP you keep for your server as long as it isn't in the scope for the local subnet.

Presuming that port 67/68 are not blocked by the router
it doesnt matter that wether you have 4 nic cards or all of them on 1 with virtual addresses
by virtual i mean..
eth0;1
eth0;2 ..

as long as u scope it correctly it will work,

Correct although ime it would be unusual for port 67/68 to be blocked unless they have been deliberately filtered. You don't need to join the DHCP server to all of the subnets, either with 4 nics or 4 virtual addresses. Using the DHCP helper, which most routers have, its unnecessary; all DHCP broadcasts will get unicast to the DHCP server. This makes everything clean and simple.

My problem is in My switch, i have only one gigabit interface where i add secondary as other network address something like virtual IPS for single interface. i added subnets in ther DHCP server. I have one NIC card. when the client requests the DHCP Server it is alocating 41.X network IP. so is there any chance to do that ?

thanks,
Srikanth

If you want to allocate addresses in 4 different subnets then you need a router to route between them. I assumed you had one. If you have no router then the DHCP will need to be a member of all 4 networks, either by 4 physical NIC connections or 4 IP's on one nic. Your DHCP server will probably assign the address pools sequentialy starting with the first IP on the nic as it has no way of differentiating which hosts you want in which subnets. You really need to either use a router or split the subnets into vlans and 802.1q trunk to the server. At least then the Bootp requests will come into the server on a VLAN specific subinterface on the nic and the DHCP server will know which pool to hand out an address from.

Otherwise the only way to ensure that your hosts get the addresses you want them to have is to enter static reservations for all of your mac addresses, which is a right pain in the bum.

You need to understand that the hosts in different subnets won't be able to talk to each other unless something is routing. Is the DHCP server also going to be serving as a router?

Hi All,

I changed the senario here. i put the dhcp server in 10.191.40.2/16 network.i configure the subnet also in 10.191.0.0/16. i given differnet scopes here the things are working. but but differnet gateways for differnet networks. how i can mention the differnet gatway in DHCP server. and another thing can we have fixed Gatway using MAC address ?

Thanks,
srikanth

ddns-update-style interim;
dynamic-bootp-lease-length 86400;
max-lease-time 604800;
default-lease-time 604800;

subnet 192.168.2.0 netmask 255.255.255.0 {
option routers 192.168.2.1;
option subnet-mask 255.255.255.0;
option broadcast-address 192.168.2.255;
option nis-domain "xyz.com";
option domain-name "xyz.com";
option domain-name-servers 192.168.2.1;
option time-offset -18000;
authoritative;
option ntp-servers 192.168.2.1;
option netbios-name-servers 192.168.2.1;
option netbios-node-type 2;
range 192.168.2.20 192.168.2.150; }
authoritative;

subnet 10.0.2.0 netmask 255.255.255.0 {
option routers 10.0.2.1;
option subnet-mask 255.255.255.0;
option broadcast-address 10.0.2.255;
option nis-domain "abc.net";
option domain-name "abc.net";
option domain-name-servers 10.0.0.1;
option time-offset -18000;
authoritative;
option ntp-servers 10.0.2.1;
option netbios-name-servers 10.0.2.1;
option netbios-node-type 2;
range 10.0.2.50 10.0.2.250; }


when you put ip address on vitural lan the dhcpd scope auto sence which interface bind with this subnet i am already using this senario but we have 4 NIC on machine and each work with define subnet have't try with Vlan