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New Contributor III

Issue with router not forwarding DHCP request to the IP helper address

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We have an office with a Netvanta 1238 with a VLAN trunk port connected to an 802.1Q interface on an Adtran 900e. The 900e interface has sub-interfaces for each of the VLANS configured on the 1238. Each sub-interface has IP helper configured pointing to our DHCP server at the Corporate office. When a new machine on one of the vlans sends a DHCP request broadcast I don't ever see this traffic on the other end. It seems the router isn't forwarding this traffic to the IP helper address.

My vlan trunk on the 1238 allows all vlan traffic. When a machine sends out a broadcast from, let's say, vlan 60, doesn't the switch tag this as vlan 60 before sending up the trunk, or am I missing something? The Router belongs to our ISP, so I don't have access to that.

Thanks,

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New Contributor III

Re: Issue with router not forwarding DHCP request to the IP helper address

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Figured it out, although there does seem to be a bug. We changed from IP Helper to DHCP relay and it started working. Routing to the helper IP was already in place. Thanks for your reply.

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Honored Contributor
Honored Contributor

Re: Issue with router not forwarding DHCP request to the IP helper address

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I'd verify routing to the helper address first. Can you ping the helper from the 900e?

Yes, if an access port on VLAN 60 sends a broadcast, the switch will tag it with VLAN 60 before sending it up a trunk port.

New Contributor III

Re: Issue with router not forwarding DHCP request to the IP helper address

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Figured it out, although there does seem to be a bug. We changed from IP Helper to DHCP relay and it started working. Routing to the helper IP was already in place. Thanks for your reply.

View solution in original post

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New Contributor III

Re: Issue with router not forwarding DHCP request to the IP helper address

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What software level are you running?

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New Contributor III

Re: Issue with router not forwarding DHCP request to the IP helper address

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I switched from using IP Helper to DHCP Relay and that fixed it.

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New Contributor III

Re: Issue with router not forwarding DHCP request to the IP helper address

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Don't know, it is the ISP's router and I don't have access.

Thanks,