I have a question i have vlan921 did not have ip address in the Core switch, I'm able to add the IP-helper to it and will not causing me any issue?

interface Vlan121
description data
no ip address 
  • 1
    There has to be a layer-3 routed interface somewhere on the VLAN that is the gateway of the VLAN in order for the DHCP traffic to be routed to the DHCP server, otherwise you need a DHCP server somewhere on the VLAN, then a helper is not needed.
    – Ron Maupin
    Commented Jan 5, 2023 at 16:14

2 Answers 2


An IP helper for DHCP relaying only works when there's an IP address configured on the SVI.

After all, it is that address that the DHCP server routes back to. It's also the address that specifies the address pool the server has to use unless the Agent Circuit ID option is used.


If a layer-3 (v4, v6, etc.) address isn't configured, then that protocol is not enabled / active on the interface. You could add all the "ip" (or "ipv6") options you want, they aren't doing anything but making the config bigger.

DHCP Relay requires an address to put in the "gateway" field, so the server knows what pool/scope to use. (if "ip" isn't enabled, DHCP relay isn't either.)

  • Thanks for your advise , i will take a look at this again and letting you know. Commented Jan 10, 2023 at 15:06

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