Multicast general question

Unanswered Question
May 20th, 2008

I am studying for BSCI and I wanted to see some multicast traffic. I've tried some LIVE radio and TV programs and they are sending data as unicast. What could it be the reason? Could it be an unoptimized setup/topology on they side or could it be something else?


I have this problem too.
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Kevin Dorrell Tue, 05/20/2008 - 01:36

You will find that a lot of, if not most, streaming of so-called "live" radio is actually unicast.

One way to generate multicast traffic for lab use is to ping the multicast address from one of your routers. For example ping repeat 100. This ping should also get a response from anything that has joined the IGMP group for that address.

Kevin Dorrell


Jon Marshall Tue, 05/20/2008 - 05:54


I nearly missed that one. Congratulations on a fantastic achievement and i know this means a lot to you.

Hopefully you won't be deserting us now you are a CCIE.


Harold Ritter Tue, 05/20/2008 - 04:34


The Internet, as it stands today, is still mostly unicast only, hence these streams being delivered via unicast.


Kevin Dorrell Tue, 05/20/2008 - 05:55

Thank you Paul and thank you Harold and Jon. It's all down to having colleagues who are patient enough to explain stuff when I didn't understand it. Thank you all, and thanks to all my other colleagues on NetPro over the years. Without you all, I don't think I ever would have made it.

I still have a lot to learn though! I've learned about MRM today!

Kevin Dorrell

(CCIE #20765)


aravindhs Tue, 05/20/2008 - 06:18

Many Congrats Kevin !!

It has always been very nice to have you around in Netpro. Hope you will still stay and provide your vaulable tips and inputs to all of us.

Very Well done !


wizassonic Tue, 05/20/2008 - 07:42

Hi there,

Thank you all for you answers !

I have 2 more questions:

1) Why are those streams delivered as unicast and not as multicast? They are well-suited for multicast, aren't they?

2) Can I see multicast traffic on the internet? How can I join as a normal user to a multicast group?


Harold Ritter Tue, 05/20/2008 - 10:02


1) The reason is that multicast capabilities are not ubiquitous in the current Internet. Some providers offer multicast content but it is usually their own and they are very protective of it.

Some streaming applications will attempt to deliver the content via multicast first and will revert to using unicast if the former is not available.

2) You could if your provider offers multicast services and if the source is connected to that same SP or to another SP to which your SP does multicast peering with, either directly or indirectly.



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