Multicasting and nat

[node@are-b.org]

Hi,

We've been offerd here to watch this seasons World Championchip Soccer/Football in HDTV via our ISP. In the letter received we where told it would be done via multicasting. E.g. we are a pilot for them to test their networking on multicasting possibilities.

Eitherway, they tell use to use VLC (videolan.org) and 'play' this file http://www.firstmovertv.nl/wk-hd.vlc so it should be quite linux friendly. Myself and friend both want to use this method and we are both behind a linux nat. nothing fancy here, except I use linux on my desktop and he uses windows.

Streaming directly to his windows laptop works fine, so everything is setup properly on his laptop, the problem arrises when we start doing it behind our linux boxen. I've read a lot about multicasting but it appears to be all about broadcasting, not simple receiving through a nat.

I've enabled
CONFIG_MULTICAST_IP=y
CONFIG_IP_MROUTE=y
CONFIG_NET_IPIP=y

on a 2.6.16-gentoo-r9 kernel. Tried it with and without mrouted. Tried it with and without the route 224.0.0.1/4 added, but don't even get a reply from ping 224.0.0.1/2/4 which I should. What else is needed to receive! multicasting on natted clients?

[thepustule]

I have been trying to do this for a while too - I set up multicasting as per the linux kernel multicasting documents and also the multicasting howtos (which are so out of date it is sad).

I tried both mrouted and smcroute, and just couldn't get it to work. mrouted would enter all of the necessary route entries in the mc_route cache but linux just wouldn't forward the packets. I tried leaving queries on this forum, and also kerneltrap. And I got no helpful replies but a lot of "I have this problem too" responses. I even found entries on the linux kernel mailing list about it. No response. No solution.

My only conclusion after wasting a lot of time and effort on this is that multicast routing is fundamentally broken in Linux 2.6 and there seems to be either no wish or no interest to fix it.

I found an old cisco router and used it instead. But it can't keep up to the bandwidth that vlc puts out.

[node@are-b.org]

So we are stuck without multicasting? That just don't sound right at all : )

Usually, this kinda 'net' stuff happens on linux before windows right? Multicasting is going to get quite some push with all the interest in offering TV via internet.

[thepustule]

I really hesitate to say "yes" because it seems like such a strange thing for the linux kernel guys to let such a big thing die. However, let me point out a couple of things to back this up in a way:

• One item is the following URL: http://www.uwsg.iu.edu/hypermail/linux/net/0601.2/0003.html Notice the references to other mailing list items from quagga and openvpn where people on those lists are also experiencing multicast weirdness.
  
  
• Also, if you look into the Documentation/networking directory in the Linux kernel source tree, and then go into multicast.txt, you will see quickly that this file has not been maintained for years. The NICs listed in that file are next-to-impossible to find these days, except in a museum.
  
  
• Same thing with the multicast howtos out there - the latest one is dated 1998. http://www.linux.org/docs/ldp/howto/Multicast-HOWTO.html
  
  
• The latest entry on the advanced-routing howto is marked "editor vacancy" and "to be continued" and some of the information found in there is quite inaccurate. http://www.tldp.org/HOWTO/Adv-Routing-HOWTO/lartc.multicast.html
  
  
• Check out my thread on kerneltrap about this http://kerneltrap.org/node/6565. Notice all of the other people with the same problem.
  

I don't know what to say, but it really seems like multicasting is dying a slow death when it comes to Linux.

[drobec]

I tried to work it out for a long time... It's working now... I just put cables from both NIC (WAN & LAN) from the server (router) to the switch together with WAN cable from the "wall" (sorry but I don't know how to explain it better). One day I just forgot to unplug them and it works

Sorry for my english

If I failed to explain how it works I could make a picture.