Multicast assignment question

[CiscoPurpleBelt]

So if I need to reserve a multicast space let's say to be used for video monitors or something, what would be the best range to use as I know many 224.0.0.X are used for certain protocol comms. Any help guys?

[Harold Ritter]

Please refer to the following white paper.

https://www.cisco.com/c/dam/en/us/support/docs/ip/ip-multicast/ipmlt_wp.pdf

Regards,

[CiscoPurpleBelt]

I am getting a not found error

[Jon Marshall]

https://www.cisco.com/c/dam/en/us/support/docs/ip/ip-multicast/ipmlt_wp.pdf

Jon

[CiscoPurpleBelt]

Thanks buddy!

I am no expert at understanding all this but looks like 239.000.000.000-239.191.255.255 would be a good range to use.

Basically, each group of hosts would be pointing to let's say 239.0.0.1 meaning I have plenty of address space to use for groups of hosts that require multicast correct?

Is it best to limit the number of host pointing to a particular multicast IP to let's say under 254?

[Harold Ritter]

Sorry for the wrong URL. I posted from my phone ;-) I corrected the link. Thanks to Jon as well for sending the proper link.

Regards,

[CiscoPurpleBelt]

I am no expert at understanding all this but looks like 239.000.000.000-239.191.255.255 would be a good range to use.

Basically, each group of hosts would be pointing to let's say 239.0.0.1 meaning I have plenty of address space to use for groups of hosts that require multicast correct?

Is it best to limit the number of host pointing to a particular multicast IP to let's say under 254?

[Harold Ritter]

Yes, the block you mentioned should be plenty of space, even for a large enterprise network.

You normally assign 1 multicast group per multicast stream, not per group of hosst. So all hosts interested to a specific stream will request their interest for that group via IGMP for ipv4 or MLD for ipv6.

There are no hard limit to the number of hosts that can join a multicast group. In principal the more hosts you have the more efficient multicast is versus unicast.

Regards

[CiscoPurpleBelt]

Hey thanks!

So any host requesting the multicast stream would need to be configured accordingly and the router would dynamically assign any address in that range?

[Harold Ritter]

The multicast source, the application streaming the video for instance, would be configured to stream the information using a specific multicast group address. The receivers, the hosts interested in that multicast stream, could be statically configured or could receive the multicast group information out of band. These hosts would in turn signal their desire to join the specific multicast group to the directly connected router using IGMP or MLD as I mentioned previously.

Regards,

[CiscoPurpleBelt]

Awesome!

In general, is the multicast group address usually 1 ip (e.g. 239.0.0.1) for a group?

I am just trying to figure out how many IPs I would have available for groups in the 239 address space.

[Harold Ritter · Accepted solution]

That is correct. 1 ip address (i.e. 239.0.0.1) = 1 ip multicast group.

Regards,

[CiscoPurpleBelt]

Ok would it be wise/best practice to have 239.0.0.1 as group 1 multicast ip, 239.0.0.2 as second group, etc.?

[Reza Sharifi]

It makes sense if you can organize them that way.  It also helps during troubleshooting.

HTH

[CiscoPurpleBelt]

For the pim rp-address, I was thinking of using let's say a 1.1.1.1 address to make things simple and unique from other subnet addresses. Would you say this is a good practice or better to use let's say 10.0.1.1?