What for: use this command in the interface configuration to prohibit broadcast packet forwarded to network subnet which is different from source packet.

Example:
- Source: 12.12.12.2/24
- Destination: 13.13.13.255/24 → broadcast address

Topology:

Configuration:

R1(config)#interface fa0/1
R1(config-if)#ip directed-broadcast

default: no ip directed-broadcast

Testing:

R2 is doing ping to 13.13.13.255

With R1 “debug ip packet” enabled:

  1. Without IP directed broadcast (by default), let see what happen in R1:

2. With IP directed broadcast (by default), let see what happen in R1:

Source:

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