Dell Force10 MXL Blade MXL 10/40GbE Switch IO Module Configuration Guide - Page 277

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 the destination address unchanged because the forwarding process is Layer 2. If you enabled UDP helper, the packet is flooded on VLAN 100 as well. Figure 14-14. UDP Helper with Configured Broadcast Addresses Packet 1 Destination Address: 1.1.255.255 VLAN 100 IP address: 1.1.0.1/24 Subnet broadcast address: 1.1.0.255 Configured broadcast address: 1.1.255.255 Hosts on VLAN 100: 1.1.0.2, 1.1.0.3, 1.1.0.4 1/1 1/2 Ingress interface IP Address: 2.1.1.1/24 UDP helper enabled Packet 2 Switched Packet Destination Address: 1.1.255.255 1/3 VLAN 101 IP address: 1.11.1/24 Subnet broadcast address: 1.1.1.255 Configured broadcast address: 1.1.255.255 Hosts on VLAN 100: 1.1.1.2, 1.1.1.3, 1.1.1.4 fnC0048mp UDP Helper with No Configured Broadcast Addresses If the incoming packet has a broadcast destination IP address, the unaltered packet is routed to all Layer 3 interfaces. If the incoming packet has a destination IP address that matches the subnet broadcast address of any interface, the unaltered packet is routed to the matching interfaces. Troubleshooting UDP Helper To display debugging information, use the debug ip udp-helper command (Figure 14-15). Figure 14-15. Debugging UDP Broadcast FTOS(conf)# debug ip udp-helper 01:20:22: Pkt rcvd on TenGig 5/0 with IP DA (0xffffffff) will be sent on TenGig 5/1 TenGig 5/ 2 Vlan 3 01:44:54: Pkt rcvd on TenGig 7/0 is handed over for DHCP processing. When using the IP helper and UDP helper on the same interface, use the debug ip dhcp command (Figure 14-16). IPv4 Routing | 275