Administrator Guide

Packet 2 is sent from the host on VLAN 101. It has a broadcast MAC address and a destination IP address of 1.1.1.255. In this case, it is
flooded on VLAN 101 in its original condition as the forwarding process is Layer 2.
Figure 55. UDP Helper with Subnet Broadcast Addresses
UDP Helper with Configured Broadcast Addresses
Incoming packets with a destination IP address matching the configured 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 configured broadcast address of VLAN 100 and 101. If
you enabled UDP helper and the UDP port number matches, the packet is flooded 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 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 56. UDP Helper with Configured Broadcast Addresses
UDP Helper with No Configured Broadcast
Addresses
The following describes UDP helper with no broadcast addresses configured.
• 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.
IPv4 Routing
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