DHCP fault tolerance

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Just been reading the ‘Microsoft’ way to set up fault tolerance for DHCP.

Basically the recommendation is to apply the 80/20 rule to split the LAN scope between 2 servers which is fair enough. However MS also recommend that 20% of the range is on a server on a remote subnet.

This is what I don’t get, I will need a compatible router to forward the DHCP broadcasts and if I don’t then I will have to install a DHCP relay agent. So why not just put the 20% on the server instead of having a relay agent? Also surely putting 20% of the IPs on a remote subnet is also a potential problem as it may be at the other end of a VPN tunnel (which may be down) or behind a router which is not functioning correctly.

Thoughts?

 

Yeah, 80/20 is fair enough but if the 20 is on another subnet then there are other factors to consider such as the router forwarding the DHCP requests which you cant assume.