IP helper-address between VLANs

Unanswered Question
Aug 25th, 2009

We have several different VLANs running on the same Catalyst 4500 switch. Our DHCP/DNS servers reside on one of these VLANs, and client PCs reside on a different VLAN. If we point our client PCs to the DHCP/DNS servers on the other VLAN, do we have to use the IP helper-address command so that the DHCP/DNS broadcasts will be forwarded to the appropriate VLAN? Even if both VLANs have SVIs (i.e. are directly connected) on the same switch?

I'm thinking that we'll still need the IP helper-address, because a VLAN is a broadcast domain and the switch, by default, won't forward broadcasts between broadcast domains.

Any thoughts are welcome, thanks.

I have this problem too.
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John Blakley Tue, 08/25/2009 - 10:22

You'll still need the helper address on the vlan that your clients will be coming into.

If you have the dhcp server in vlan 10, and your clients are in vlan 20, you'll point to the dhcp server's address from vlan 20:

int vlan 20

ip address

ip helper-address

int vlan 10

ip address

Your server is for instance.




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