Reference Guide

432 | IPv4 Routing
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Figure 20-12. Configuring a Broadcast Address
View the configured broadcast address for an interface using the command show interfaces, as shown in
Figure 20-13.
Figure 20-13. Configuring a Broadcast Address
Configurations Using UDP Helper
When UDP helper is enabled and the destination IP address of an incoming packet is a broadcast address,
FTOS suppresses the destination address of the packet. The following sections describe various
configurations that employ UDP helper to direct broadcasts.
• UDP Helper with Broadcast-all Addresses on page 432
• UDP Helper with Subnet Broadcast Addresses on page 433
• UDP Helper with Configured Broadcast Addresses on page 434
• UDP Helper with No Configured Broadcast Addresses on page 434
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 20-14:
1. Packet 1 is dropped at ingress if no UDP helper address is configured.
FTOS(conf-if-vl-100)#ip udp-broadcast-address 1.1.255.255
FTOS(conf-if-vl-100)#show config
!
interface Vlan 100
ip address 1.1.0.1/24
ip udp-broadcast-address 1.1.255.255
untagged GigabitEthernet 1/2
no shutdown
R1_E600(conf)#do show interfaces vlan 100
Vlan 100 is up, line protocol is down
Address is 00:01:e8:0d:b9:7a, Current address is 00:01:e8:0d:b9:7a
Interface index is 1107787876
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