Users Guide

UDP Helper with Subnet Broadcast
Addresses
When the destination IP address of an incoming packet matches the subnet broadcast address of any
interface, the system changes the address to the configured broadcast address and sends it to matching
interface.
In the following illustration, Packet 1 has the destination IP address 1.1.1.255, which matches the subnet
broadcast address of VLAN 101. If you configured UDP helper and the packet matches the specified UDP port,
the system changes the address to the configured IP broadcast address and floods the packet on VLAN 101.
Packet 2 is sent from the host on VLAN 101. It has a broadcast MAC address and a destination IP address of
1.1.1.255. In this case, it is flooded on VLAN 101 in its original condition as the forwarding process is Layer 2.
Figure 46. UDP Helper with Subnet Broadcast Addresses
UDP Helper with Configured Broadcast
Addresses
Incoming packets with a destination IP address matching the configured broadcast address of any interface
are forwarded to the matching interfaces.
In the following illustration, Packet 1 has a destination IP address that matches the configured broadcast
address of VLAN 100 and 101. If you enabled UDP helper and the UDP port number matches, the packet is
flooded on both VLANs with an unchanged destination address.
Packet 2 is sent from a host on VLAN 101. It has broadcast MAC address and a destination IP address that
matches the configured broadcast address on VLAN 101. In this case, Packet 2 is flooded on VLAN 101 with
IPv4 Routing 436