Configuration restrictions and guidelines
The receiving of directed broadcasts to a directly connected network is disabled by default on the switch. As a result, UDP helper is available only when the ip forward-broadcast command is configured in system view. For more information about reception and forwarding of directed broadcasts to a directly connected network, see "Configuring IP performance optimization."
A UDP helper enabled device must not forward DHCP broadcast packets that use destination port 67 or 68. Therefore, the UDP port numbers set with the udp-helper port command must not include 67 or 68.
You can specify a port number or the corresponding parameter for a UDP port to forward packets. For example, udp-helper port 53 and udp-helper port dns specify the same UDP port number.
The configuration of all UDP ports is removed if you disable UDP helper.
You can configure up to 256 UDP port numbers to enable the forwarding of packets with these UDP port numbers.
You can configure up to 20 destination servers on an interface.