1-2Table 1-1 List of default UDP portsProtocol UDP port numberDNS (Domain Name System) 53NetBIOS-DS (NetBIOS Datagram Service) 138NetBIOS-NS (NetBIOS Name Service) 137TACACS (Terminal Access Controller AccessControl System) 49TFTP (Trivial File Transfer Protocol) 69Time Service 37Configuring UDP HelperFollow these steps to configure UDP Helper:To do… Use the command… RemarksEnter system view system-view —Enable UDP Helper udp-helper enable RequiredDisabled by default.Specify a UDP port numberudp-helper port { port-number| dns | netbios-ds | netbios-ns| tacacs | tftp | time }OptionalBy default, the device enabledwith UDP Helper forwards thebroadcast packets containingany of the six port numbers 53,138, 137, 49, 69 and 37.Enter VLAN interface view interface Vlan-interfacevlan-id —Specify the destination serverto which the UDP packets areto be forwardedudp-helper server ip-addressRequiredNo destination server isspecified by default.z You need to enable UDP Helper before specifying any UDP port to match UDP broadcasts;otherwise, the configuration fails. When the UDP helper function is disabled, all configured UDPports are disabled, including the default ports.z The dns, netbios-ds, netbios-ns, tacacs, tftp, and time keywords correspond to the six defaultports. You can configure the default ports by specifying port numbers or the correspondingparameters. For example, udp-helper port 53 and udp-helper port dns specify the same port.z You can specify up to 20 destination server addresses on a VLAN interface.z If UDP Helper is enabled after a destination server is configured for a VLAN interface, thebroadcasts from interfaces belonging to the VLAN and having a matching UDP port will be unicastto the destination server.
