topic Re: Profiling with DHCP (IP Helper) in Network Access Control

Profiling with DHCP (IP Helper)

jpfowler5 — Fri, 02 Feb 2018 17:40:18 GMT

How do I get DHCP information to ISE from a switch that is running the DHCP server? When I'm pointing to an external DHCP server using IP helper on the SVI works like a charm, but I don't know how to do this when the DHCP server is on the switch.

Thanks for any advice

Re: Profiling with DHCP (IP Helper)

hslai — Fri, 02 Feb 2018 17:47:57 GMT

If the switch handing off the DHCP assignment, then it does not forward the requests to another, such as ISE. Thus, we need either use an external DHCP server and ip-helper or use a SPAN port for ISE to capture the DHCP requests.

Re: Profiling with DHCP (IP Helper)

paul — Sat, 03 Feb 2018 16:53:09 GMT

Jacob,

Did you test adding the IP helper to the switch? I am pretty sure I tested this and the switch will still serve up DHCP and forward the DHCP packets. Remember IP helper is not just used for DHCP forwarding. It has other functions like Wake on LAN directed broadcast forwarding and other uses.

Re: Profiling with DHCP (IP Helper)

Craig Hyps — Mon, 05 Feb 2018 13:45:04 GMT

The local router/switch will not serve and also forward. Other than changing DHCP to be centralized, the recommended option here is Device Sensor as local SPAN is not feasible.