How does the computer know which device on the network to query? How does the default gateway factor into this? Pretty much, what is the chain of events that occurs when a computer tries to obtain an IP address using DHCP?
The reason I ask is because I'm trying to figure out how to best set up a redundant DHCP server, in case the original fails for whatever reason.
Best Answer
It doesn't know what device to query. Thus it broadcasts its request to the entire subnet. The DHCP server is listening for a certain type of communication and when it hears that specific broadcast it begins the DHCP conversation with the device that broadcasted its request. Take a look at the DORA process for more information.
DORA stands for:
As for the gateway, it can come into play only if it explicitly forwards DHCP traffic to another subnet. That feature is usually called DHCP Relay. Otherwise the gateway ignores the broadcast DHCP message just like it ignores every other broadcast message.
As for redundant DHCP servers, you'll want to keep them both on the same subnet and probably use the 80/20 rule. You can set up failover if you're using CentOS as your DHCP server.