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
â—† Up to 20 helper addresses can be specified with this command.
â—† 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.
â—† The UDP packets to be forwarded must be specifed by the ip forward-
protocol udp command, and the packets meet the following criteria:
â–
The MAC address of the received frame must be all-ones broadcast
address (ffff.ffff.ffff).
â–
The IP destination address must be one of the following:
â–
all-ones broadcast (255.255.255.255)
â–
subnet broadcast for the receiving interface
â–
The IP time-to-live (TTL) value must be at least 2.
â–
The IP protocol must be UDP (17).
â–
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.
â—† 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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