Frame Tagging

Simon Hobson dhcp1 at
Thu Aug 15 12:09:13 UTC 2013

Steven Carr wrote:
>Correct, typically when you deploy this type of DHCP the DHCP server
>"lives" in it's own network, or does in some cases provide DHCP to the
>local subnet, but the remote subnets use IP helpers to forward the
>initial DHCP broadcast requests. If you had an IP helper on the same
>subnet then the DHCP server would see the same request twice, first
>from broadcast, second via IP helper.

That's cetainly true with just a plain switch. The question was more about switches with DHCP snooping capabilities - eg to add Option 82 and so on. At which point I realise I was half asleep when I wrote the last message and wasn't differentiating in my mind between configuring a DHCP Helper (which as you say wouldn't remove the original broadcast packet), and DHCP Snooping which may or may not depending on what the switch was designed to do.

IIRC the original suggestion was to apply DHCP Helpers, and remove the VLAN traffic from the server - thus isolating the server from the networks it's serving. That may or may not work depending on whether there are other reasons you need the server connected to those VLANs.

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