Dell Force10 MXL Blade - UDP Helper with Subnet Broadcast Addresses; UDP Helper with Configured Broadcast Addresses

274 | IPv4 Routing
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Figure 14-12. UDP helper with All Broadcast 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 a matching
interface.
In Figure 14-13, 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 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 14-13. 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 Figure 14-14, 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.
P
acket 1
D
estination Address:
2
55.255.255.255
1/1
Ingress interface
IP Address: 2.1.1.1/24
UDP helper enabled
1/2
1/3
VLAN 100
IP address: 1.1.0.1/24
Subnet broadcast address: 1.1.0.255
Configured broadcast address: 1.1.255.2
55
Hosts on VLAN 100: 1.1.0.2, 1.1.0.3, 1.1.0.4
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
Packet 2
Switched Packet
TLV 1
Chassis ID
Preamble
Start Frame
Delimiter
Destination MAC
(01:80:C2:00:00:0E)
Source MAC
Ethernet Type
(0x88CC)
LLDPDU
Padding
FCS
TLV 2
Port ID
TLV 3
Port Description
TLV 4
System Name
TLV 5
System Description
TLV 6
System Capabilities
TLV 7
Management Addr
TLV 0
End of LLDPDU
TLV 127
Organizationally Specific