Usage Example
In networking every machine is given a unique IP address. Groups of machines with similar addresses are considered to be part of the same logical subnet. One method of assigning IPs is DHCP in which IPs are given out by single server machine. Normally this machine is on the same subnet as its clients and can answer to their broadcasted DHCP requests. However, in some situations the server is on a different subnet. The problem with this is that most routers in their default state do not pass broadcast messages to machines outside the physical subnet. Such messages are essential to the normal operation of certain network services such as DHCP.
To resolve this a UDP Helper Address is established in the router configuration to forward broadcast network traffic from the PCs to the DHCP server. The DHCP server responds with a unicast IP address from the given range. It reserves the IP address for the time it can calculate that it can get a response. If the client responds again with a broadcast it distributes the IP address. A helper address can also be used to forward certain other UDP network configuration messages. As a result a UDP helper address is sometimes created to allow two server machines to communicate across different subnets.
Read more about this topic: UDP Helper Address
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