another dhcp problem

[Ahmed Malik]

hi,

attached is the pkt trcer file and what i want to achieve is to provide ips through my dhcp server all over the network. i am using three routers and three switches. the routers are running RIPv2 protocol. and the dhcp server is running on ip 172.16.10.2, the dns server is on 172.16.10.3. the routers can communicate with one another successfully.

Now for the network on the extreme left side, the ip pool i defined in the dhcp server is 192.168.5.11 and so on. now whts confusing me is that where should i use the ip helper address command or it can be done some other way?

Plz do run this file and let me know what changes to make.

Regards,

Ahmed

[Vaibhava Varma]

Hi Ahmed

Unfortunately I can not open the packet trace file as I have not installed the same but as the genral concept of implenting DHCP Relay below are my inputs.

1. Enable DHCP Relay at the GW Interface for the LAN Subnet using "ip helper-address" command

e.g) for the DHCP Scope 192.168.5.X the "ip helper-address" needs to defined at the GW SVI or GW dot1q of the GW Physical Interface for the 192.168.5.X Subnet.

2. Ensure routing is available from the LAN GW for the DHCP Scope Subnet ie 192.168.5.X and the DHCP Server

172.16.10.2 so basically there should be routing available in the network between the DHCP Server and the LAN Subnet GW and the best way to verify would be to ping from the LAN Segment usinh Source IP as the GW IP of the DHCP Scope Pool to the DHCP Server. If that works clients would for sure get the IPs from DHCP Server.

Hope this helps to answer your query regarding this setup.

Regards

Varma

[Ahmed Malik]

here is the img of my configuration.

[cadet alain · Accepted solution]

Hi,

1)Your default gateway in your DHCP pool should be in the same subnet as the pool so 192.168.5.1

2) Now when a DHCP server is in a different subnet than the hosts you must use a DHCP relay and that is what the ip helper-address is doing.It is translating the broadcast requests from the hosts into unicast so you must configure it under the interface facing the host and the address must be the unicast address of the server so here on R2:

int f0/1

ip helper-address 172.16.10.2

Regards.

Alain.

[Latchum Naidu · Accepted solution]

Ahmed,

As others told, your DHCP must be able to communicate with other subnets like 192.168.5.0 192.168.6.0 etc.,
And if you have other subnets in you LAN, make sure they are able to reach each other (inter vlan routing)

After all configuration is fine, you need to tell the LAN facing interface (for example R1 interface Fa0/0 is connected to LAN 192.168.5.0) to send the dhcp query to the dhcp server, the below command does this.

int fa0/0
ip helper-address "dhcp server ip" on which you have defined the subnets

Please rate the helpfull posts.
Regards,
Naidu.