1. It is flooded on VLAN 101 without changing the destination address because the forwarding process is Layer 2.2. If you enabled UDP helper, the system changes the destination IP address to the configured broadcast address 1.1.255.255 andforwards the packet to VLAN 100.3. Packet 2 is also forwarded to the ingress interface with an unchanged destination address because it does not have broadcastaddress configured.Figure 38. UDP Helper with Broadcast-All AddressesUDP Helper with Subnet Broadcast AddressesWhen the destination IP address of an incoming packet matches the subnet broadcast address of any interface, the system changesthe 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 VLAN101. If you configured UDP helper and the packet matches the specified UDP port, the system changes the address to theconfigured 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, itis flooded on VLAN 101 in its original condition as the forwarding process is Layer 2.Figure 39. UDP Helper with Subnet Broadcast AddressesUDP Helper with Configured Broadcast AddressesIncoming packets with a destination IP address matching the configured broadcast address of any interface are forwarded to thematching interfaces.In the following illustration, Packet 1 has a destination IP address that matches the configured broadcast address of VLAN 100 and101. If you enabled UDP helper and the UDP port number matches, the packet is flooded on both VLANs with an unchangeddestination address.330 IPv4 Routing
