Has any one every tried using a single DHCP server to administer addresses to clients on different vlan subnets.

Ex. Vlan1 192.168.1.0 /24 , Vlan2 192.168.2.0/24, Vlan 3 192.168.3.0 /24, …………

How would the DHCP server know which scope to use? IP helper on the router in someway does it??

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quote:

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Originally posted by whytokayok
How would the DHCP server know which scope to use? IP helper on the router in someway does it??

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Just to be sure I got it..... The requesting interface would be in this case lanwould be the routers subinterface for the vlan(s).

Thanks

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quote:

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Originally posted by whytokayok
Just to be sure I got it..... The requesting interface would be in this case lanwould be the routers subinterface for the vlan(s).

---

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Forwarding of Broadcast Packets and Protocols

There are circumstances in which you want to control which broadcast packets and which protocols are forwarded. You do this with helper addresses and the
forward-protocol commands.

The ip helper-address interface subcommand tells the router to forward UDP broadcasts, including BootP, received on this interface. (UDP is the connectionless
alternative to TCP at the Transport Layer.) Use the ip helper-address interface subcommand to specify the destination address for forwarding broadcast packets. Full
command syntax follows.

ip helper-address address
no ip helper-address address

The address argument specifies a destination broadcast or host address to be used when forwarding such datagrams. You can have more than one helper address per
interface. You remove the list with no ip helper-address.

If you do not specify a helper address command, the router will not forward UDP
broadcasts.

Example:

This example defines an address that act as a helper address.

ip helper-address 121.24.43.2

The ip forward-protocol global configuration command allows you to specify which protocols and ports the router will forward. Its full syntax is listed next.

ip forward-protocol {udp|nd|spanning-tree} [port]
no ip forward-protocol {udp|nd|spanning-tree} [port]

The keyword nd is the ND protocol used by older diskless SUN workstations. The keyword udp is the UDP protocol. A UDP destination port can be specified to
control which UDP services are forwarded. By default both UDP and ND forwarding are enabled if a helper address has been defined for an interface. If no ports are
specified, these datagrams are forwarded, by default:

Trivial File Transfer (TFTP)

Domain Name System

IEN-116 Name Server

Time service

NetBios Name Server

NetBios Datagram Server

Boot Protocol (BootP) client and server datagrams

TACACS service

Use the no ip forward-protocol command with the appropriate keyword and argument to remove the protocol.

Example:

The example below first defines a helper address, then uses the ip forward-protocol command to specify forwarding of UDP only.

interface ethernet 1
ip helper-address 131.120.1.0
ip forward-protocol udp

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Thanks..... I ran across a situation that will require several VLANS using DCHP to distribute the addresses for each subnet. This implementation of VLANS is not discussed in the switching (BCMSN) or routing (BSCN) courses offered by Cisco. As matter of fact the Switching course did not cover IP helper at all.

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