Dell Force10 MXL Blade - Port Channel Commands

IPv4 Routing | 275
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
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
When using the IP helper and UDP helper on the same interface, use the debug ip dhcp command
(Figure 14-16).
P
acket 1
D
estination Address:
1
.1.255.255
1/1
Ingress interface
IP Address: 2.1.1.1/24
UDP helper enabled
1/2
1/3
VLAN 100
IP address: 1.1.0.1/24
Subnet broadcast address: 1.1.0.255
Configured broadcast address: 1.1.255.2
55
Hosts on VLAN 100: 1.1.0.2, 1.1.0.3, 1.1.0.4
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
fnC0048m
p
Packet 2
Switched Packet
Destination Address:
1.1.255.255
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.