If you are wondering why:

ping 224.0.0.1

does not give you anything back from your localhost or other hosts that are running Linux kernel 2.6, it is because, in Linux kernel 2.6, the capability of ICMP to reply to broadcast/multicast ping message is disabled by default. Whereas, it is enabled by default in Linux kernel 2.4.

Therefore, the solution will be to enable that capability by typing:

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

Now those systems should be able to reply the ICMP request packets that are sent to multicast address 224.0.0.1.

Archive: Linux Kernel's Networking Part (IPv4 Multicast)