Network devices

Hello everybody,

well, I’m a little bit new in the field and I am trying to get the max amount of information about multicast.
I wanna know how to chose the right switches for a topology that contains more than 400 guests in a local IPTV system?

thanks in advance :smiley: and excuse my English XD.

Hi Anas,

I would first figure out what your multicast design will exactly look like. You need to get some questions answered:

* Do you only need multicast within a VLAN or does it have to be routed?
* How many multicast groups will there be? Your devices have to keep up with the number of IGMP groups and if your multicast is routed, you have to keep track of all multicast routes.
* How many simultaneous receivers do you have?
* What are your bandwidth requirements?
* How many packets per second per stream?
* What is the packet size?

Once you have your numbers, you can check some switches and see if they support what you need and what they are capable of performance-wise. To give you a quick example, here’s a Cisco 3750 with the default SDM template:

SW1#show sdm prefer
 The current template is "desktop default" template.
 The selected template optimizes the resources in
 the switch to support this level of features for
 0 routed interfaces and 255 VLANs. 

  number of unicast mac addresses:                  8K
  number of IPv4 IGMP groups + multicast routes:    1K
  number of IPv4 unicast routes:                    10K
    number of directly-connected IPv4 hosts:        8K
    number of indirect IPv4 routes:                 2K
  number of IPv6 multicast groups:                  0
  number of directly-connected IPv6 addresses:      0
  number of indirect IPv6 unicast routes:           0
  number of IPv4 policy based routing aces:         0
  number of IPv4/MAC qos aces:                      0.5K
  number of IPv4/MAC security aces:                 0.875k
  number of IPv6 policy based routing aces:         0
  number of IPv6 qos aces:                          0
  number of IPv6 security aces:                     0

It’s capable of keeping track of 1K IGMP + multicast routes with this template.
You can find its performance statistics in the datasheet:

This will tell you how many packets per second the switch can handle and its maximum throughput.

Hope this helps to get you started :slight_smile:


thanks for your responsiveness Mr @ReneMolenaar,
can you please tell me when can we chose multicast within Vlan or routed and how can i verify the packets per second per stream that i will need?
it is required to use VLANs?
yeah i m a noob XD

Hi Anas,

The bandwidth required and packets per second depends on your application. It’s best to check with the vendor of the application what they have to say about this.

About routing and VLANs, that’s not a simple question to answer :slight_smile: This really depends on your requirements and network. Some things you might want to think about:

* Is this network only for multicast traffic or do you also have other traffic
* Is this for a local network or do you need to stream over WAN links to remote sites?
* How many multicast groups do you have
* Should all receivers be able to receive all multicast groups
* Should there be any separation between groups / receivers.


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Hi Mr @ReneMolenaar,

for example, if it’s about a local VDI network, with about 60 multcasts (TV services).

thanks in advance.

Hi Anas,

You mean 60 different multicast groups? And you mentioned 400 users?

If we only look at the multicast part and ignore other stuff (like security) then you could start by crunching some numbers to get an idea of how much bandwidth you need.

Just to give you a quick example, let’s say you have an 4K Ultra HD video that requires 25 Mbps of bandwidth.

Let’s say we have a simple topology that looks like this:


If you only have one multicast group and let’s say 60 users on SW2 then you only need to send 1x 25 Mbps on the link from SW1 to SW2.

SW2 still has to forward 60x 25 Mbps on its interfaces.

If you have 60 active multicast groups and let’s say 10 receivers on SW2 (each user is receiving multiple streams) then you’ll have 60x 25 Mbps = 1500 Mbps on the link from SW1 to SW2…quite a difference from the first scenario.


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in a real case from a friend who s working on a topology with 230 client; he told me that he has a problem with the switches (hp 1920 jg926a). as he told me, the stream stops for about 3 min.

what can he do in this case ?

Hello Anas

There is not enough information to be able to diagnose something like this. Do you have any more information about the implementation so we can get a clearer picture of the problem?


well i m a little bit new in multicast,so just tell me what kynd of info do you need?

Hello Anas

In order to be able to help in such a situation, we’d need to know the network topology, the subnets implemented and the configuration of the IGMP protocol and the multicast environment. Where is the multicast stream source, on the network itself or off site?

The other problem is that most of our experience here at Networklessons is centred around Cisco certifications and thus on Cisco devices.