Udp Helper With Broadcast-All Addresses; Udp Helper With Subnet Broadcast Addresses - Dell S4820T Configuration Manual

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UDP Helper with Broadcast-All Addresses

When the destination IP address of an incoming packet is the IP broadcast address, Dell Networking OS

rewrites the address to match the configured broadcast address.

In the following illustration:

Packet 1 is dropped at ingress if you did not configure UDP helper address.

If you enable UDP helper (using the ip udp-helper udp-port command), and the UDP

destination port of 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 you

do not configure an IP broadcast address (using the ip udp-broadcast-address command) on

VLANs 100 or 101, the packet is forwarded using the original 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:

It is flooded on VLAN 101 without changing the destination address because the forwarding process

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.

Packet 2 is also forwarded to the ingress interface with an unchanged destination address because it

does not have broadcast address configured.

Figure 50. UDP Helper with Broadcast-All 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

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

IPv4 Routing