Directed Broadcasts & Security

What is a Directed Broadcast address?

An address used to target all devices on a specific, remote subnet.

What is an example of a broadcast address

If the network is 172.31.0.0 (Class B), the Directed Broadcast is 172.31.255.255.

How do you create a broadcast address for any specific network?

You turn ALL bits in the Host Portion to 1s.

Do modern routers forward Directed Broadcasts by default?

No

To calculate a Broadcast Address, you must turn all Host bits to 1. When you convert this to Dotted Decimal, what number does that octet become?

255. (Because 11111111 in binary = 255 in decimal)

Why don’t modern routers forward Directed Broadcasts by default?

They are disabled by default on modern Cisco IOS to prevent security attacks.

What is a Smurf Attack?

A Denial of Service (DoS) attack that exploits Directed Broadcast

how does a smurf attack work

The attacker spoofs the victim's IP as the "Source" and sends a ping to a Directed Broadcast address. Every device on that network replies to the victim, overwhelming them.

Why is a Directed Broadcast attack considered an "Amplification" attack?

Because 1 packet sent by the attacker triggers hundreds or thousands of replies (one from every device on the target subnet) directed at the victim.