Configurations Using Udp Helper; Udp Helper With Broadcast-All Addresses - Dell Z9500 Configuration Manual

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Internet address is 1.1.0.1/24

IP UDP-Broadcast address is 1.1.255.255

MTU 1554 bytes, IP MTU 1500 bytes

LineSpeed auto

ARP type: ARPA, ARP Timeout 04:00:00

Last clearing of "show interface" counters 00:07:44

Queueing strategy: fifo

Input Statistics:

0 packets, 0 bytes

Time since last interface status change: 00:07:44

Configurations Using UDP Helper

When you enable UDP helper and the destination IP address of an incoming packet is a broadcast address, Dell Networking OS

suppresses the destination address of the packet.

The following sections describe various configurations that employ UDP helper to direct broadcasts.

UDP Helper with Subnet Broadcast Addresses

UDP Helper with Configured Broadcast Addresses

UDP Helper with No Configured Broadcast Addresses

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 is Layer 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.

IPv4 Routing