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2. If you enabled UDP helper, the system changes the destination IP address to the configured broadcast address 1.1.255.255 and
forwards the packet to VLAN 100.
3. Packet 2 is also forwarded to the ingress interface with an unchanged destination address because it does not have broadcast address
configured.
Figure 46. UDP Helper with Broadcast-All Addresses
UDP Helper with Subnet Broadcast Addresses
When the destination IP address of an incoming packet matches the subnet broadcast address of any interface, the system changes the
address to the configured broadcast address and sends it to matching interface.
In the following illustration, Packet 1 has the destination IP address 1.1.1.255, which matches the subnet broadcast address of VLAN 101. If
you configured UDP helper and the packet matches the specified UDP port, the system changes the address to the configured IP
broadcast address and floods the packet on VLAN 101.
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 47. 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.
IPv4 Routing
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