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Local Broadcast and Directed Broadcasts - Demo and Packet Captures
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- Опубліковано 14 сер 2024
- In this video we'll pick apart Broadcasts -- specifically the difference between a Local Broadcast and a Directed Broadcast (which is sometimes referred to as a Targeted Broadcast).
We'll run through a few demonstrations of either type of broadcast. Then fire up Wireshark and take a look at the packets as they appear on the wire. This will illustrate clearly the difference between Layer 2 Broadcasts and Layer 3 Broadcasts.
This is the "long version" of this video. In the shorter version we simply talk through the concepts and do a couple ping tests.
00:00 - Start / Topology Introduction
00:22 - Definition of a Broadcast
00:47 - L2 Broadcast vs L3 Broadcast
01:35 - Local Broadcast
02:12 - Pinging the Local Broadcast
03:21 - Wireshark - Looking at a Unicast Ping
04:10 - Wireshark - Pinging the Local Broadcast IP address
05:18 - Directed Broadcast (Targeted Broadcast)
05:49 - Wireshark - Pinging the Directed Broadcast IP of the Local Subnet
08:34 - Directed Broadcasts for Foreign Networks
10:29 - Wireshark - Studying a Unicast ping to a foreign network
12:00 - Wireshark - Pinging the Directed Broadcast IP of a Foreign Subnet
13:57 - Directed Broadcast starts as Unicast, then becomes Broadcast
15:59 - Summary
16:34 - Security Implication of Directed Broadcasts
17:18 - Enabling Directed Broadcast on Cisco Routers and Linux Hosts
18:31 - Outro
Link to correlating article which includes PCAP files you can download:
www.practicaln...
I'm doing something different with this... I'm releasing 3 versions of this content: An Article, a Short Video, and a Long video. Pick your favorite =).
Article www.practicalnetworking.net/stand-alone/local-broadcast-vs-directed-broadcast/
Short Video ua-cam.com/video/ZNXDbzaAM-I/v-deo.html
Long Video ua-cam.com/video/ny6MsSLb8_o/v-deo.html
Wish I could give you more likes. These are the kind of practical contents that I have been looking for, for so long. Thanks. Keep posting more videos like these. :)
Thank you for the kind words, Vidhya. Glad you enjoyed this content!
Your channel is digital gold, and I really mean it ...
Thank you for the kind words, Cokegen =). Much appreciated.
straight to the point !! thank Ed :)
Damn I tried explaining this exact information to someone over chat yesterday but this video illustrates it so much better! Thanks a million I have linked them to this fantastic explanation.
Thanks for your support =)
Great, great, great video. Thanks.
Very great video!
Thanks!
Great content. Thank you sir
Please keep uploading, this is great!
That's the plan =)
This lecture awesome ...keep going
Thank you, I will=)
Excellent video
Thank you very much!
Hi this is Noor one of your viewers thank you for shooting of such a nice videos, could pleas share how to install GNS3 and let me know about it, I mean could you please make a video on GNS3 installation and setup, how to configure it to function proper.
Hi Noor, glad you enjoyed the video =).
I don't presently have plans for GNS 3 installation videos, but David Bombal has some good resources on the topic:
ua-cam.com/users/DavidBombalsearch?query=gns3
Very informative
Thank you. =)
Awesome!
=)
If I connected a computer to Hub1 and addressed it with 10.1.2.2/24, would it receive a Local Broadcast (255.255.255.255) from 10.1.1.1? The two machines would be on the same L2 network and on different L3 networks.
Fun question... I would guess Yes, it would receive it. Sounds like something you should lab out =)
All your videos are awesome and very helpful to clear core network concept. I am waiting for your course on ipsec and ssl vpn(asa) , bgp on udemy.
Thanks for the kind words, Deepak. =)
Thanks for the video, it's great!
I'd like to ask you if I have to enable the direct-broadcast option only on the interface connected to the network I want to do the direct broadcast (for example the interface of the ip 10.3.3.3) or to every interface on every router on which the ping will make its way?
I've read your article, thanks!
Excellent question. You only need the `ip directed-broadcast` command on the router interface that would be expected to deliver directed broadcasts. So, in the example of the video it would be on R3's interface with the IP 10.3.3.3 -- the one facing Host 5/6/7.
Glad you enjoyed the video and the article!
In the case of a company's topology that contains branch offices with various subnets and VLANs, can Direct Broadcast be used to troubleshoot connectivity and reachability issues at Layer 2 and Layer 3 levels? If this is one use case, are there other use cases of using Directed Broadcast when troubleshooting issues in modern network topologies? I would think Firewalls, DMZs, Proxy Servers, VPNs, WLANs and WANs are security considerations which will block or drop a Directed Broadcast packet whenever a Directed Broadcast is used as a troubleshooting tool.
You're on the right track... but keep in mind:
(a) Most routers block directed broadcast to limit abuse
(b) Most hosts don't respond to broadcasts by default
So while in theory, you're right about the benefit for troubleshooting. In practice, the two points above would limit the effectiveness of troubleshooting with broadcast packets.
I've tried to replicate the same exact lab using eigrp but im not getting the same ICMP requests for broadcasts any idea why? Also what routing protocol did you use in this lab?
Hi Caesar. I'm fairly certain I just used static routes. Did you enable directed broadcast on all the Router interfaces? What about on the hosts?
If I want to ping all the L2 Switches of a single site (whose management IP addresses are in same as Core switch )from core switch of that site , how to execute it ?
If all the management IP's are in the same Subnet, it would be as simple as pinging the directed broadcast IP address of that Subnet. Keep in mind, not all switches respond to broadcast pings by default.
Does this Local Broadcast address, 255.255.255.255, come with a /32 mask?
It sort of doesn't have a mask. It's a single IP, so you could argue it has a /32 mask. But it's somewhat an independent concept from subnet masking.
😮