Users Guide

3. Packet 2 is also forwarded to the ingress interface with an unchanged destination address because it does not have
broadcast address configured.
Figure 41. UDP Helper with Broadcast-All Addresses
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 42. 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.
IPv4 Routing 360