Multicast on loopback device?

Multicast on loopback device?

Post by Chris Willi » Sun, 08 Sep 1996 04:00:00

I'd like to work at home on my linux box on some multicast applications.
At work this is OK because I can test the programs using different machines on
the local network and to/from machines on other networks but this isn't possible
from home.

I am hoping that its possible to multicast to the loopback device from one shell
and receive the multicast messages from the loopback device in another shell?
What I've tried so far (but it doesn't work) is:
route add -net netmask dev lo

I then get from netstat -r:
Kernel routing table
Destination     Gateway         Genmask         Flags Metric Ref Use    Iface
loopback        *            U     0      0       11 lo       *            U     0      0        1 sl0

My sending program appears to send messages to the loopback device (the TX_OK
field of netstat -i increases correctly according to the amount of data I send).
However the receiving program gives a perror message:
ADD MEMBERSHIP: Cannot assign requested address
(for the case of itself looking for a suitable interface). If I tell it (via a
command line option to try interface lo, the perror message is:
ADD MEMBERSHIP: No such device
(which is very strange)

I have mrouted available but there doesn't seem a logical way to configure tunnel
endpoints in this situation - but of course I'm open to suggestions.

Output form dmesg includes:
Linux IP multicast router 0.06.
(I think thats enough isn't it?)

Kernel version is 2.0.11.

Any ideas anyone? I haven't found anything covering this in the HOW-TO's.



1. Multicast on loopback device? PS.

A small correction to the netstat -r output in my last post>

The device for the line is usually lo for the situation I described. I
inadvertently swiped an output from another experiment I was trying while I had a
SLIP connection (so it incorrectly said sl0 instead of just lo).


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