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PXE DHCP forwarding

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itangir
Occasional Collector

PXE DHCP forwarding

We're transitioning from using DHCP options 66 and 67 for PXE booting as it's unsupported and problematic.

 

Apparently the right way to do this is to forward the DHCP requests to the DHCP server and the PXE server. This will let the DHCP server reply an IP and the PXE server respond to option 60 and negotiate the NBP and all that.

 

Refer to this post for a better sum up of the PXE DHCP process.

 

 

I'm struggling to determine the best way to accomplish this across different VLANs. My go-to attempt was to do this:

 

ip helper-address <ip of DHCP server>

ip helper-address <ip of PXE server>

 

 

But it didn't seem to like this approach. My thought was that having multiple IP helper-addresses defined would query both simultaneously. Maybe it just picks one at random though? That wouldn't work since the PXE client would need DHCP replies from both servers.

 

If I pass the ip-helper to the broadcast IP of the VLAN with both servers:

 

ip helper-address 10.1.50.255

 

It works. But I don't really like this approach because it seems like it would pass a lot of broadcast traffic onto the server VLAN if I had to set it up for each client VLAN.

 

Is there a better way to accomplish this goal on the switching? What method(s) do you guys use?

2 REPLIES
Vince-Whirlwind
Honored Contributor
Solution

Re: PXE DHCP forwarding

2 IP-helper addresses.

The DHCP broadcast gets forwarded to both.

itangir
Occasional Collector

Re: PXE DHCP forwarding

That's what I tried first but wasn't working. However, I just retried it for sanity and it's fine now.

 

Not sure if I originally mistyped an IP or maybe there was just some residual stuff on the client or networking. Either way, it looks like it's working as intended now.