Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
Community Member

ip helper

Hi all, if I have a switch with 3 vlans, and 1 windows dhcp server, Do I need to issue the command once, or on each vlan ?

5 REPLIES
Community Member

Re: ip helper

Each vlan interface that will receive dhcp requests will need the ip helper command.

Purple

Re: ip helper

any subnet that is not directly attached to the dhcp server subnet will need the helper statement .

Green

Re: ip helper

You'd need an IP Helper on each router / L3 interface that is not a member of the VLAN on which the DHCP server resides.

You don't mention it specifically, but you will need a router or L3 switch to get the VLANs to talk to each other.

The IP Helper goes on the client-side of the router and points to the DHCP server.

Good Luck

Scott

Community Member

Re: ip helper

If you do enable the ip helper-address on each VLAN remember that it impliciitly enables fowarding of several different kinds of UDP broadcasts.

udp tftp

udp nameserver

udp domain

udp time

etc

this may not be desirable

Mark

Silver

Re: ip helper

Basically, "ip helper" command forwards broadcast as unicasts to the specified address. The command is issued for every Interface VLAN (broadcast domain) from which you want to forward broadcasts to some destinations (e.g. DHCP server, TFTP server, and so on)

188
Views
0
Helpful
5
Replies
CreatePlease to create content