Users Guide
1. It is ooded on VLAN 101 without changing the destination address because the forwarding process is Layer 2.
2. If you enabled UDP helper, the system changes the destination IP address to the congured 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 congured.
Figure 53. 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 congured 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 congured UDP helper and the packet matches the specied UDP port, the system changes the address to the
congured IP broadcast address and oods 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 ooded on VLAN 101 in its original condition as the forwarding process is Layer 2.
Figure 54. UDP Helper with Subnet Broadcast Addresses
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.
414
IPv4 Routing