topic IP Directed Broadcast in Network Security

IP Directed Broadcast

avilt — Fri, 21 Feb 2020 12:48:06 GMT

I have a 2901K9 router at a remote location. Insite Interface = 10.10.10.1/24 Outside Interface = 20.20.20.1/24

I have set "no ip directed boradcast" on both interfaces. ( I think it's the default settings)

But still when I ping 20.20.20.255 I get a reply from 10.10.10.1

How can I disable this?

IP Directed Broadcast

Amjad Abdullah — Thu, 13 Dec 2012 04:03:46 GMT

I think you need an ACL to disable this.

Modified as wrong info provided. Amjad

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IP Directed Broadcast

avilt — Mon, 17 Dec 2012 05:24:24 GMT

That's surprising, then what is the need to run "no ip directed broadcast" command at the interface level?

IP Directed Broadcast

turnera — Mon, 17 Dec 2012 16:57:48 GMT

Directed broadcasts allow a remote device to send a broadcast message to a network segment using a single unicast packet. Once reaching the layer 3 device directly connected to the network for which the broadcast is intended the message is sent as a link-layer broadcast to all hosts on a network segment. The directed broadcast feature is often targeted in a Distributed Denial of Service (DDoS) because a single unicast packet can result in a very large number of replies. The directed broadcast feature should be disabled.

Re: IP Directed Broadcast

Amjad Abdullah — Tue, 18 Dec 2012 03:02:16 GMT

Avilt: I fully mi-understood your question. Ignore my reply above and take the other answer from turnera which is the one describing directed broadcast accurately.
As this is a wireless forum can you move the thread to the appropriate forum so you get better help?

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IP Directed Broadcast

avilt — Wed, 19 Dec 2012 02:25:00 GMT

I am aware of ip directed broadcast. My question is why is it not affective inspite of having the command at interface level?

I have a router at the remote location.

Inside Interface = 10.10.10.1/24 Outside Interface = 20.20.20.1/24

I have set "no ip directed boradcast" on both interfaces. ( I think it's the default settings in the latest IOS)

But still when I ping 20.20.20.255 from my location, I get a reply from 10.10.10.1 which is the inside interface of the remote router.

IP Directed Broadcast

avilt — Thu, 06 Jun 2013 04:20:19 GMT

Can any one provide me the explanation?

I have a router at the remote location.

Inside Interface = 10.10.10.1/24 Outside Interface = 20.20.20.1/24

I have set "no ip directed boradcast" on both interfaces. ( I think it's the default settings in the latest IOS)

But still when I ping 20.20.20.255 from my location (remotely), I get a reply from 10.10.10.1 which is the inside interface of the remote router.

Re: IP Directed Broadcast

Richard Burts — Fri, 07 Jun 2013 22:46:24 GMT

The answer requires a correct understanding of what the command is intended to do. The command is intended to prevent receiving a packet with destination of broadcast address and forwarding it as a broadcast onto the local subnet. The command is working as intended since the packet is not forwarded. What you are observing is the router, acting as a host, responding to the packet but not forwarding the packet.

HTH

Rick

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