I think he said he has one DHCP server, so this example shows three
different DHCP servers. Also, in this example you will not need an IP
helpder address for the DHCP server that is connected directly to this
segment, in this example you will not need "ip helper-address 10.70.48.48"
under interface vlan 1.
One common application that requires helper addresses is Dynamic Host
Configuration Protocol (DHCP), which is defined in RFC 1531. DHCP protocol
information is carried inside of BOOTP packets. To enable BOOTP broadcast
forwarding for a set of clients, configure a helper address on the router
interface closest to the client. The helper address should specify the
address of the DHCP server. If you have multiple servers, you can configure
one helper address for each server. Since BOOTP packets are forwarded by
default, DHCP information can now be forwarded by the router. The DHCP
server now receives broadcasts from the DHCP clients.
It's not that Cisco thinks should be forwarded as well but the "ip
helper-address" by nature of it's feature forward all this UDP broadcast.
It is correct to limit these UDP that are not needed to be no forwarded.
>From: "Patrick Ramsey"
>Reply-To: "Patrick Ramsey"
>To: [EMAIL PROTECTED]
>Subject: Re: DHCP Requests across VLANs [7:8689]
>Date: Fri, 15 Jun 2001 14:38:28 -0400
>
>Start a session with the router and insert a 'ip helper' address.
>
>Be carefull though...by default, for whatever reason, cisco thinks netbios
>broadcast and name resolution along with dns and a few other broadcasts
>should be forwarded as well. You'll need to manually shut these off via
>'no
>ip forward'
>
>example:
>
>interface Vlan1
> ip address 10.40.48.1 255.255.240.0
> ip helper-address 10.70.48.48
> ip helper-address 10.70.80.30
> ip helper-address 10.70.80.33
> ipx network 104048
>
>Then in global config do the following:
>
>no ip forward-protocol udp tftp
>no ip forward-protocol udp domain
>no ip forward-protocol udp time
>no ip forward-protocol udp netbios-ns
>no ip forward-protocol udp netbios-dgm
>
>
>-Patrick
>
>
> >>> "Vlade" 06/15/01 10:44AM >>>
>There is an easy Win NT solution. You can have a one of the servers or
>workstations act as a DHCP relay for the other subnets. They will listen
>dor
>DHCP broadcats and forward them to the proper DHCP server.
>""[EMAIL PROTECTED]"" wrote in
>message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> > Hi all,
> >
> > In a Cat6509, we have created three VLANs. In one of the three VLANs, an
>NT
> > Server is configured as a DHCP Server. My doubt no.1 is..... Can a
>client
>in
> > another VLAN get its DHCP request served by this DHCP Server. If yes,
>how
> > this can be done. If not, is there any other way we can have all the
>clients
> > in the three VLANs get IP Address from a single DHCP Server.
> >
> > My doubt no.2 is slightly off topic. If the clients in all three VLANs
>can
> > get IP Address from the NT DHCP Server, Can I give IP Addresses from a
>single
> > DHCP Scope.
> >
> > Thanks in Advance!
> >
> > S.Kalidasan
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