DHCP helper

NetworkAdmin — Sat, 28 Dec 2019 00:31:58 GMT

Hello,

We run a single core (X690) with edge switches throughout our network. I’ve been tasked with setting up a new NAC (Network Address Control) tool. Per the setup instructions for the tool, we need to setup dhcp helpers for all our vlans. However, we currently already have bootprelay setup as below:

configure bootprelay add IP-nactool vr VR-Default

configure bootprelay add IP-existingDHCPServer vr VR-Default

enable bootprelay ipv4 vr-Default

For a couple of vlans we need to point directly to the ip address of the dhcp handler for our nac tool, which I’ve been able to accomplish by doing

configure bootprelay vlan Registration_NAC_VLAN add IP_dhcp_NAC_handler

The issue I’ve run into , is that in order for all our other active vlans to properly show data in the NAC tool, we need to relay all the dhcp/ip info from the other vlans. However, if I do the following command:

configure bootprelay vlan Production_VLAN add ip_of_nac_tool

Current DHCP handout by existing DHCP server breaks. (Since the nac tool doesn’t have anything to handout). Does anyone have any suggestions? Is the best thing here to switch to udp profile? I have never used this, as I am new to extreme and also relatively green with networking in general. I have read in documentation that you cannot have both bootprelay and UDP profile setup side by side. Has anyone run into this?

Thank you,

Re: DHCP helper

FredrikB — Mon, 30 Dec 2019 00:11:27 GMT

If your DHCP server is on the same VLAN as the clients, it should receive the DHCPDISCOVERs despite the bootprelay setting. What actually “breaks”? Does the DHCP server never get the discover packets? Try adding the DHCP server as bootprelay as well (shouldn’t be needed, but...).

/Fredrik

Re: DHCP helper

NetworkAdmin — Thu, 06 Feb 2020 07:01:57 GMT

Hi FredrikB,

I figured this out - it “breaks” because it only uses the specific dhcp server defined for the vlan. In a way overwriting the global bootprelay setting. DHCP server is on different vlan from clients.

Thanks!

topic Re: DHCP helper in ExtremeSwitching (EXOS/Switch Engine)

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