Setup Guide
UDP Helper with Congured Broadcast Addresses
Incoming packets with a destination IP address matching the congured broadcast address of any interface are forwarded to the matching
interfaces.
In the following illustration, Packet 1 has a destination IP address that matches the congured broadcast address of VLAN 100 and 101. If
you enabled UDP helper and the UDP port number matches, the packet is ooded on both 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 that matches the congured
broadcast address on VLAN 101. In this case, Packet 2 is ooded on VLAN 101 with the destination address unchanged because the
forwarding process is Layer 2. If you enabled UDP helper, the packet is ooded on VLAN 100 as well.
Figure 58. UDP Helper with Congured Broadcast Addresses
UDP Helper with No Congured Broadcast Addresses
The following describes UDP helper with no broadcast addresses congured.
• 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 for troubleshooting, use the debug ip udp-helper command.
Example of the debug ip udp-helper Command
DellEMC(conf)# debug ip udp-helper
01:20:22: Pkt rcvd on Te 5/1 with IP DA (0xffffffff) will be sent on Te 5/2 Te 5/3 Vlan 3
01:44:54: Pkt rcvd on Te 7/1 is handed over for DHCP processing.
When using the IP helper and UDP helper on the same interface, use the debug ip dhcp command.
Example Output from the debug ip dhcp Command
Packet 0.0.0.0:68 -> 255.255.255.255:67 TTL 128
2017-08-05 11:59:35 %RELAY-I-PACKET, BOOTP REQUEST (Unicast) received at interface
172.21.50.193 BOOTP Request, XID = 0x9265f901, secs = 0 hwaddr = 00:02:2D:8D:46:DC,
giaddr = 0.0.0.0, hops = 2
IPv4 Routing
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