How to configure Linux to Support Multicast IP

Most Linux systems have multicast IP capability turned off by default. In order to use multicast sockets on my Linux system, I had to reconfigure and build my kernel, and then run the following command as root after re-booting:

route add -net netmask dev lo

Make sure that this route has been added by typing route -e

You should see output like this:

markw@colossus:/home/markw > su
markw # route add -net netmask dev lo
colossus:/home/markw # route -e
Kernel IP routing table
Destination Gateway Genmask Flags MSS Windowirtt Iface
loopback * U 3584 0 0 lo * U 3584 0 0 lo
markw #

Please note that I ran the route commands as root. I don’t permanently add this route for multicasting to my Linux development system; rather, I manually add the route (as root) when I need to use multicast IP. Re-configuring and building the kernel is also fairly simple. On my Linux system, I use the following steps to configure and build a
new kernel with multicast IP support:

1. cd /usr/src/linux
2. make menuconfig select networking options check the box labeled “enable multicast IP” save and exit from  menuconfig
3. make dep; make clean; make zImage
4. cp /vmlinux /vmlinux_good
5. cp arch/i386/boot/zImage /vmlinux
6. cd /etc
7. edit lilo.conf, adding a new entry for the /vmlinux_good kernel
8. lilo

Posted on: 18/12/2009

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