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DarkFiber

IP Multicast

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IP Multicasting

 

Why Do You Need Multicasting?

 

“Necessity is the mother of all invention,” a saying derived from Plato’s Republic, holds very true in the world of technology. In the late 1980s, Dr. Steve Deering was working on a project that required him to send a message from one computer to a group of computers across a Layer 3 network. After studying several routing protocols, Dr. Deering concluded that the functionality of the routing protocols could be extended to support “Layer 3 multicasting.” This concept led to more research, and in 1991, Dr. Deering published his doctoral thesis, “Multicast Routing in a Datagram Network,” in which he defined the components required for IP multicasting, their functions, and their relationships with each other.

 

The most basic definition of IP multicasting is as follows:

Sending a message from a single source to select multiple destinations across a Layer 3 network in one data stream.

 

If you want to send a message from one source to one destination, you could send a unicast message.

If you want to send a message from one source to all the destinations on a local network, you could send a broadcast message. However, if you want to send a message from one source to selected multiple destinations spread across a routed network in one data stream, the most efficient method is IP multicasting.

 

Demand for multicast applications is increasing with the advent of such applications as audio and video web content; broadcasting TV programs, radio programs, and concerts over the Internet;

communicating stock quotes to brokers; transmitting a corporate message to employees; and transmitting data from a centralized warehouse to a chain of retail stores.

Success of one-to-many multicast applications has created a demand for the second generation of multicast applications that are referred to as “many-to-many” and “many-to-few,” in which there are many sources of multicast traffic. Examples of these types of applications include playing games on an intranet or the Internet and conducting interactive audio and video meetings.

Check attachment for IP multicast summary explanation & cmds

IP_Multicast.doc

Edited by DarkFiber
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Hey Dark,

 

No Questions as i just downloaded the document and haven't read it yet :)

But just want to say thankyou for this and the other documents you have made. I have got the IPv6 one you wrote as well

 

Thankyou So much Great help. !

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I'm a big fan, I've been looking for a secondary source to read and this works out great. To tell you the truth, this document reads better then the chapter about "Multicasting" in the Cisco Press Certification Guide. You've got a knack for teaching.

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I'm sorry! I was unable to open the file. It seems the file is corrupt. Can I get it from anywhere else?

 

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Thanks again for these docos. Certainly helped me understand M/C more, which helped me pass my BSCI today.

 

Cheers!

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Thanks again for these docos. Certainly helped me understand M/C more, which helped me pass my BSCI today.

 

Cheers!

 

 

Congrats :)

Glad it helped you :)

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Hello Guys , any questions : )

 

Hi is it possible to have more than one eigrp ip summary address under one interface.

 

Thanks

Edited by rhamietron
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Hi is it possible to have more than one eigrp ip summary address under one interface.

 

Thanks

 

Kindly post your question in th EIGRP thread, thats the multicast :)

 

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Thank you... Is there any document for implementing IP MULTICAST OVER MPLS DOMAIN...plz send it to vijayaramaraju@ceeyes.com,vijayraju11@yahoo.com...urgent..

 

Thanks once again.

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Hello Guys , any questions : )

 

Hi

 

can you take a look at this post pls. h**p://www.sadikhov.com/forum/index.php?showtopic=172130

 

i am trying to find an easy way to chk if a network is capable of sending multicast traffic

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But i've got one question about BSR.

What is the difference between BSR and mapping agent (send-rp-discovery) ? I don't understand this part of the PIM. And what means the parameter hash-mask-length of the command ip pim bsr-candidate?

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But i've got one question about BSR.

What is the difference between BSR and mapping agent (send-rp-discovery) ? I don't understand this part of the PIM. And what means the parameter hash-mask-length of the command ip pim bsr-candidate?

 

(send-rp-discovery) = mapping agent for PIM auto-rp protocol

 

(ip pim bsr-candidate) = mapping agent for PIM BSR protocol

 

hash-mask-length for BSR is like a subnet mask so the RP can be responsible for multiple multicast groups

Length of a mask (32 bits maximum) that is to be ANDed with the group address before the hash function is called. All groups with the same seed hash (correspond) to the same RP. For example, if this value is 24, only the first 24 bits of the group addresses matter. This fact allows you to get one RP for multiple groups.

 

Hope its more clear

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So hash-mask-length is used for load balancing between two or more RPs?

And one more: AutoRP is for cisco devices, and BSR is for non-cisco devices. Am i right?

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So hash-mask-length is used for load balancing between two or more RPs?

And one more: AutoRP is for cisco devices, and BSR is for non-cisco devices. Am i right?

 

kind of, aut-rp is a cisco proprietary , BSR is not.

BSR can work with cisco or any other vendor

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I have had a look at this post, EIGRP and OSPF they are very nice. But where is IS-IS.

 

If you can provide one that would be great

 

:D

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I have had a look at this post, EIGRP and OSPF they are very nice. But where is IS-IS.

 

If you can provide one that would be great

 

:D

 

Thanks. will do so sooon, BGP, ISIS & MPLS in February

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HI Folks,

 

Nice website with bunch of good topics. I have a question regarding multicasting. I know what it is. Source sent a single stream to multiple recipients. How about receiving?

 

O.k For my home network everybody is constantly on youtube.com watching movies. I do have a cisco router 2610 for my router/firewall. Can I configure the router for multicast to send only a single stream from youtube to everyone in my LAN? (suppose everyone is watching the same movie).

 

How about if they are watching different movies but STILL ON YOUTUBE? Thank you for your replies. I couldn't fine anything doing searches and of course don't know what I am looking for.

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Hi,

 

If you say that you know what it is, that means you know the source announces itself by sending multicast traffic. The receivers announce themself by sending Join messages for the multicast group they are interested in (sparse mode deployment) or receive the multicast traffic by doing nothing and just waiting for the traffic to be flooded in the multicast network (dense mode deployment). One important note is that the network between source and receivers must be configured to forward multicast traffic. If the Youtube's servers would be the "multicast sources" (which I don't believe they are), than all the routers between those sources and your LAN must be multicast enabled. Not only yours, but your ISP's too and all the upstream routers until the last router directly connected to the source.

 

Today, multicast is not a feature world wide deployed, in the public Internet. Multicast is deployed in the operators' networks, in the corporates' private networks/backbones to support videoconference, IPTV and other services. I know there is a public network multicast aware being deployed, call Mbone, but currently it's in testing.

 

Youtube service is an "on demand" service. You choose the video (which is a record stored on the servers) and the servers start streaming the content. This is done by unicast means using Streaming protocols like Real Time Streaming Protocol (control protocol- setup, maintain, teardown the unicast session) and Real Time Protocol (transport protocol which actually carries the data packets). So for each user a different RTSP session is established, even if multiple users want to watch the same video. It's like you having a server with a multitude of videos/movies and you offer your friends the possibility to see any of those videos. But your don't play it continuously, you start playing it only when is it requested.

 

 

Edited by andr2ea_g
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Hi,

 

If you say that you know what it is, that means you know the source announces itself by sending multicast traffic. The receivers announce themself by sending Join messages for the multicast group they are interested in (sparse mode deployment) or receive the multicast traffic by doing nothing and just waiting for the traffic to be flooded in the multicast network (dense mode deployment). One important note is that the network between source and receivers must be configured to forward multicast traffic. If the Youtube's servers would be the "multicast sources" (which I don't believe they are), than all the routers between those sources and your LAN must be multicast enabled. Not only yours, but your ISP's too and all the upstream routers until the last router directly connected to the source.

 

Today, multicast is not a feature world wide deployed, in the public Internet. Multicast is deployed in the operators' networks, in the corporates' private networks/backbones to support videoconference, IPTV and other services. I know there is a public network multicast aware being deployed, call Mbone, but currently it's in testing.

 

Youtube service is an "on demand" service. You choose the video (which is a record stored on the servers) and the servers start streaming the content. This is done by unicast means using Streaming protocols like Real Time Streaming Protocol (control protocol- setup, maintain, teardown the unicast session) and Real Time Protocol (transport protocol which actually carries the data packets). So for each user a different RTSP session is established, even if multiple users want to watch the same video. It's like you having a server with a multitude of videos/movies and you offer your friends the possibility to see any of those videos. But your don't play it continuously, you start playing it only when is it requested.

 

 

Thanks, your explanation helped me put all the pieces together.

Edited by jthong555
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Thanks, your explanation helped me put all the pieces together.

 

I am glad if it helped.

 

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