Chapter 30
| IP Interface Commands
IPv4 Interface
– 921 –
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 specified 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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