480 | IPv4 Addressingw w w . d e l l . c o m | s u p p o r t . d e l l . c o m In Figure 21-15, Packet 1 has the destination IP address 1.1.1.255, which matches the subnet broadcastaddress of VLAN 101. If UDP helper is configured and the packet matches the specified UDP port, thenthe system changes the address to the configured IP broadcast address and floods the packet on VLAN101.Packet 2 is sent from host on VLAN 101. It has a broadcast MAC address and a destination IP address of1.1.1.255. In this case, it is flooded on VLAN 101 in its original condition as the forwarding process isLayer 2.Figure 21-15. UDP helper with Subnet Broadcast AddressesUDP Helper with Configured Broadcast AddressesIncoming packets with a destination IP address matching the configured broadcast address of any interfaceare forwarded to the matching interfaces.In Figure 21-16, Packet 1 has a destination IP address that matches the configured broadcast address ofVLAN 100 and 101. If UDP helper is enabled and the UDP port number matches, the packet is flooded onboth 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 thatmatches the configured broadcast address on VLAN 101. In this case, Packet 2 is flooded on VLAN 101with the destination address unchanged because the forwarding process is Layer 2. If UDP helper isenabled, the packet is flooded on VLAN 100 as well.Figure 21-16. UDP Helper with Configured Broadcast AddressesTLV 1Chassis IDPreamble Start FrameDelimiterDestination MAC(01:80:C2:00:00:0E)Source MAC Ethernet Type(0x88CC)LLDPDU Padding FCSTLV 2Port IDTLV 3Port DescriptionTLV 4System NameTLV 5System DescriptionTLV 6System CapabilitiesTLV 7Management AddrTLV 0End of LLDPDUTLV 127Organizationally SpecificPacket 1Destination Address:1.1.255.2551/1Ingress interfaceIP Address: 2.1.1.1/24UDP helper enabled1/21/3VLAN 100IP address: 1.1.0.1/24Subnet broadcast address: 1.1.0.255Configured broadcast address: 1.1.255.255Hosts on VLAN 100: 1.1.0.2, 1.1.0.3, 1.1.0.4VLAN 101IP address: 1.11.1/24Subnet broadcast address: 1.1.1.255Configured broadcast address: 1.1.255.255Hosts on VLAN 100: 1.1.1.2, 1.1.1.3, 1.1.1.4fnC0048mpPacket 2Switched PacketDestination Address:1.1.255.255
