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Roberto-9646 asked Roberto-9646 commented

DHCP Failover

Hello.

I just setup DHCP Failover, in load balancing mode on two Windows Server 2019.

The two servers are on the server VLAN while clients are on client VLANs.
The router has now three ip_helpers (one for pxe, and the other two for the dhcp servers).

On a client I setup a check to make sure clients receive IP configuration.

The (strange to me) behaviour I see is that the test reports it gets two replies (one from each dhcp server). Luckily it shows that both dhcp servers agree on the ip address for the client. It also confirms that the dhcp servers are the two in the DHCP failover.

If I stop the dhcp server on one of the hosts, the check reports as expected only the dhcp_offer from the host that has the service running.

Can anybody confirm that is the expected behaviour? I thought that the two dhcp

Thank you and best regards.
Roberto

windows-serverwindows-dhcp-dns
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1 Answer

LimitlessTechnology-2700 avatar image
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LimitlessTechnology-2700 answered Roberto-9646 commented

Hello Roberto,

This is expected. I have seen it in a different tested environment. But basically since the Discovery SYN is a broadcast, it will be received and trigger the SYN/ACK from the available DHCP. You know the system is working find since both DHCP synchronize on the pool handling.

Hope this clarifies your question,



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Hi @LimitlessTechnology-2700

Ok, thank you.

I'll take that as correct. Although, I believe it's not correct to talk about SYN and ACK, but instead it's DHCPDISCOVER and DHCPOFFER.

Thank you again and best regards.
Roberto

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