Multicast Video over IP

Daniel A-S

Daniel A-S

Member
Hi,

I'm on site and having a bit of difficulty with getting a multicast video stream to work.

I don't really understand multicasting, do multicast addresses work on top of standard IP address, for example we have a bit of kit with the IP address 192.168.1.10 which needs to talk to a multicast address, surely our equipment needs to be at least on the same subnet as the equipment multicasting?

So our kit (192.168.1.10/24) would need to be on the same subnet as the host multicaster which might be for example 192.168.1.20/24?

Multicasting does not operate outside of layer 3 rules does it? My receiver won't receive multicast packets from a device that's on a different subnet in a layer 2 network? I don't understand how multicast could talk across subnets?

Any anybody can share any informtation on this I'd appreciate it. I'd do some more searching around but I'm under time pressure, really just need some understanding of this.

Thanks
 
beers

beers

Moderator
Staff member
What kind of application are they implementing?

IP 224.0.0.0/4 is assigned for multicasting, the host side would be assigned by the client application to listen on the particular multicast address that's transmitting information. The NIC uses IGMP to join a multicast group from the upstream router. You don't have to change any current addressing, these sit on top of existing addresses.

Are they trying to multicast from multiple sites or is it just local?
 
Daniel A-S

Daniel A-S

Member
Ah ok, so it doesn't really matter what IP our host receiver has, just so long as it's looking at the correct multicast address?

The stream is unfortunately travelling through several locations quite a distance, it's a 20Mbit video stream encoded in mpeg2. The switch at our end is a juniper which is managed by some externally, I've asked them to make sure IGMP is enabled in the switchports configuration.

The stream is coming from a single location.

Thanks
 
Daniel A-S

Daniel A-S

Member
We are said to have a layer 2 direct transparent connection, no port blocking, just a straight forward layer 2 network. The chain unfortunately consists of a mixture of switches, these include Cisco and Juniper.

Apparently the mac addresses of either end can been seen.

Annoyingly we don't have control of the network side of things, this is outsourced, otherwise I'd have a tinker with the configuration.

We're pressuring the network administrators to look into this at the moment.

Thanks for your help anyway
 
beers

beers

Moderator
Staff member
Yuck layer 2 WAN :p

With everything on the same subnet you should be able to see the traffic from that particular multicast address in a capture like with Wireshark.
 
Daniel A-S

Daniel A-S

Member
lol Yeah layer 2 over that distance seems kind of crumby...

Turns out it was IGMP not enabled in the Juniper switch, the network admin enabled it and the stream came to life.

Thanks for your help
 
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