An Open Access Peon

11 June 2006

What the ping?

I've been trying to get multicast working on my home ADSL router (a Linux-based PC using a Speedtouch 'frog' USB modem). This is because the BBC and several UK ADSL providers are running multicast trials, including my own ISP Plus.net. While Plus.net seem to have multicast enabled (I see the IGMP messages on the ppp device), getting Linux to actually do something multicast routing wise seems to be one of those "if you're in the club" topics: the preserve of those who find command-line interfaces exciting.

Out-of-date documentation annoyances - if you've read the incomplete multicast routing howto it ends (before the "to be continued") with pinging the 'all-hosts' group (224.0.0.1) to see who'll respond, except sometime between when that was written circa 1999 and now, responding to broadcast packets was disabled by default. If you want your Linux-kernel machine to respond do:

echo 0 >/proc/sys/net/ipv4/icmp_echo_ignore_broadcasts

Now, assuming multicast is alive and well on the Linux router and my Windows XP PC the next step is to get some routing going between the LAN and ADSL. I'm currently battling xorp, which seems to get horribly confused by an interface on an IPv6 enabled machine but which doesn't have an IPv6 address. Like, say, like the ADSL PPP connection? (NB I have IPv6 courtesy of a tunnel to the BT broker service - not that there's much out there in IPv6 land. I'm not even going to go near the kernel patches required to make multicast routing work on IPv6.)

And the purpose of this fruitless exercise? In the UK the BBC and ITV terrestial stations are broadcasting the World Cup, both of which should be on the multicast ... laptop + multicast TV = portable World Cup!

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