Udp Helper With Broadcast-All Addresses; Udp Helper With Subnet Broadcast Addresses - Dell Force10 C150 Configuration Manual

UDP Helper with Broadcast-all Addresses

When the destination IP address of an incoming packet is the IP broadcast address, FTOS rewrites the
address to match the configured broadcast address.
In Figure 21-14:
1. Packet 1 is dropped at ingress if no UDP helper address is configured.
2. If UDP helper (using the command
the packet matches the UDP port configured, the system changes the destination address to the
configured broadcast 1.1.255.255 and routes the packet to VLANs 100 and 101. If an IP broadcast
address is not configured (using the command
packet is forwarded using the original destination destination IP address 255.255.255.255.
Packet 2, sent from a host on VLAN 101 has a broadcast MAC address and IP address. In this case:
1. It is flooded on VLAN 101 without changing the destination address because the forwarding process is
Layer 2.
2. If UDP helper is enabled, 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 21-14. UDP helper with All Broadcast Addresses
Packet 1
Destination Address:
255.255.255.255
Ingress interface
IP Address: 2.1.1.1/24
UDP helper enabled
Packet 2
Switched Packet

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.
ip udp-helper udp-port
ip udp-broadcast-address
1/1 1/2
1/3
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
) is enabled, and the UDP destination port of
) on VLANs 100 or 101, the
VLAN 100
IP address: 1.1.0.1/24
Subnet broadcast address: 1.1.0.255
Configured broadcast address: 1.1.255.255
Hosts on VLAN 100: 1.1.0.2, 1.1.0.3, 1.1.0.4
IPv4 Addressing | 479