About IP Helper

IP Helper is not supported for WAN interfaces or for interfaces that are configured for NAT.

Many User Datagram Protocols (UDP) rely on broadcast/multicast to find its respective server, usually requiring their servers to be present on the same broadcast subnet. To support cases where servers lie on different subnets than clients, a mechanism is needed to forward these UDP broadcasts/multicasts to those subnets. This mechanism is referred to as UDP broadcast forwarding. IP Helper helps broadcast/multicast packets to cross an appliance’s interface and be forwarded to other interfaces based on policy. IP Helper allows the appliance to forward DHCP requests originating from its interfaces to a centralized DHCP server.

IP Helper supports user-defined protocols and extended policies. IP Helper provides better control on existing NetBIOS/DHCP relay applications. Some of the built-in applications that have been extended are:

Extended Built-in Relay Applications

Protocol	UDP Port Number
DHCP	67/68
DHCPv6	546, 547
Net-Bios NS	137
Net-Bios Datagram	138
DNS	53
Time Service	37
Wake on LAN (WOL)
mDNS	5353 Multicast address: 224.0.0.251