Re: Multicasting past routers?
Re: Multicasting past routers?
- Subject: Re: Multicasting past routers?
- From: Tomas Zahradnicky <email@hidden>
- Date: Thu, 25 Mar 2004 08:39:06 +0100
Josh,
Multicast has to be enabled in a router. A device and router use
IGMP to communicate memberships to multicasts. Most of "the
internet" does not support multicast routing to the best of my
knowledge.
OK.
The AirPort base station is not a router. It's a NAT device.
Well you're right but it behaves like router doesn't it?
The difference is that the NAT device mangles the packets in order
to make it appear as though packets from a number of machines came
from one IP address. I have no idea how or if most NATs support
multicast. My guess is that most NAT devices do not support
multicast.
Ari Suutari (natd's author): Since natd operates on IP level I think
that multicast UDP packets should work in similar manner as any other
UDP packet. If you run natd with -verbose flag you'll see what
happens when a packet arrives.
I'll definitely try to run it in verbose mode and see what happens
since my conclusions may be useful to other people.
You may also need to use the socket options to join the multicast
group before sending.
Even before sending? I thought I need to join the group in order to
receive multicast datagrams.
This will trigger the stack to use IGMP to join the multicast group.
If you have a router that does handle multicast routing, this will
notify the router you are interested in sending and receiving
packets on that multicast.
I'll try that.
Thanks,
Tomas
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