274 | IPv4 Routingw w w . d e l l . c o m | s u p p o r t . d e l l . c o m Figure 14-12. UDP helper with All Broadcast AddressesUDP Helper with Subnet Broadcast AddressesWhen the destination IP address of an incoming packet matches the subnet broadcast address of anyinterface, the system changes the address to the configured broadcast address and sends it to a matchinginterface.In Figure 14-13, Packet 1 has the destination IP address 1.1.1.255, which matches the subnet broadcastaddress of VLAN 101. If you configured UDP helper and the packet matches the specified UDP port, thesystem changes the address to the configured IP broadcast address and floods the packet on VLAN 101.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 14-13. 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 14-14, Packet 1 has a destination IP address that matches the configured broadcast address ofVLAN 100 and 101. If you enabled UDP helper and the UDP port number matches, the packet is floodedon both VLANs with an unchanged destination address.Packet 1Destination Address:255.255.255.2551/1Ingress 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, 1.1.1.4Packet 2Switched PacketTLV 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 Specific
