C
HAPTER
44
| IP Interface Commands
IP Interface
– 1017 –
ip helper-address This command specifies the application server or subnet (indicated by a
directed broadcast address) to which designated UDP broadcast packets
are forwarded. Use the no form to remove a UDP helper address.
SYNTAX
[no] ip helper-address ip-address
ip-address - Host address or directed broadcast address to which
UDP broadcast packets are forwarded. (Range: 1-65535)
DEFAULT SETTING
None
COMMAND MODE
Interface Configuration (VLAN)
COMMAND USAGE
◆ Up to 20 helper addresses can be specified with this command.
◆ To forward UDP packets with the UDP helper, the clients must be
connected to the selected interface, and the interface configured with
an IP address.
◆ The UDP packets to be forwarded must be specifed by the ip forward-
protocol udp command, and the packets meet the following criteria:
■
The MAC address of the received frame must be all-ones broadcast
address (ffff.ffff.ffff).
■
The IP destination address must be one of the following:
■
all-ones broadcast (255.255.255.255)
■
subnet broadcast for the receiving interface
■
The IP time-to-live (TTL) value must be at least 2.
■
The IP protocol must be UDP (17).
■
The UDP destination port must be TFTP, Domain Name System
(DNS), Time, NetBIOS, BOOTP or DHCP packet, or a UDP port
specified by the ip forward-protocol udp command.
◆ If a helper address is specified with this command, but no UDP ports
have been specified with the ip forward-protocol udp command,
broadcast traffic for several UDP protocol types will be forwarded by
default as described under the ip forward-protocol udp command.
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