Ip Helper; Ip Directed Broadcast - Allied Telesis SwitchBlade x908 Series Software Reference Manual

Internet Protocol (IP) Addressing and Protocols

IP Helper

The IP Helper feature allows the switch to receive UDP broadcasts on one subnet, and
forward them as broadcasts or unicasts into another subnet, so a client can use an application
which uses UDP broadcast (such as Net-BIOS) when the client and server are located in
different subnets. The IP Helper feature forwards UDP broadcast network traffic to specific
hosts on another subnet and/or to the broadcast address of another subnet.
When the IP Helper feature is enabled on a VLAN interface, the UDP broadcast packets
received on the interface are processed for forwarding out through another interface into
another subnet. Depending on the nature of the ip-helper addresses configured, the UDP
broadcasts will be unicast forwarded to a single host in the destination subnet, or unicast
forwarded to multiple hosts in the destination subnet, or broadcast to the broadcast address of
the destination subnet. Not all UDP broadcasts will be forwarded when IP Helper is configured.
The set of broadcasts to be forwarded can be defined by specifying the destination UDP
port(s) of the packets you wish to forward.
The command to enable the forwarding of UDP broadcasts received on a given interface is
helper-address
command specifies types of broadcast packets to forward.
Multiple different destination addresses can be specified by using multiple instances of the
helper-address
actually the broadcast address of one of the subnets directly connected to the switch, then the
UDP packets will be forwarded as broadcasts onto that subnet.
Likewise, multiple different types of UDP packet can be specified for forwarding by specifying
multiple different destination ports using the
Note:

IP Directed Broadcast

IP directed-broadcast is enabled and disabled per VLAN interface. When enabled a directed
broadcast packet is forwarded to an enabled VLAN interface if received on another subnet.
An IP directed broadcast is an IP packet whose destination address is a broadcast address for
some IP subnet, but originates from a node that is not itself part of that destination subnet.
When a directed broadcast packet reaches a switch that is directly connected to its destination
subnet, the packet is flooded as a broadcast on the destination subnet.
The
reach target subnets. The command affects the final transmission of the directed broadcast on
its destination subnet. It does not affect the transit unicast routing of IP directed broadcasts. If
directed broadcast is enabled for an interface, incoming directed broadcast IP packets intended
for the subnet assigned to interface will be flooded as broadcasts on that subnet.
If the no ip directed-broadcast command is configured for an interface, directed broadcasts
destined for the subnet where the interface is attached will be dropped instead of broadcast.
22.14
(entered in interface configuration mode). The
command under the same interface. If a destination address is specified that is
The types of UDP broadcast packets that the switch will forward are ONLY those
specified by the ip forward-protocol command(s). There are not other UDP packet
types that the IP helper process forwards by default.
ip directed-broadcast command controls the flooding of directed broadcasts when they
Software Reference for SwitchBlade® x908, x900 and x600 Series Switches
TM
AlliedWare Plus Operating System - Software Version 5.3.1
ip forward-protocol udp
ip forward-protocol udp command.
ip
ip
C613-50007-01 REV B