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On Debian 12.04 LTS

I am trying to access the key net.ipv4.conf.all.mc_forwarding by doing :

sudo sysctl -w net.ipv4.conf.all.mc_forwarding=1

But every time I am doing this, I get the message

error: permission denied on key 'net.ipv4.conf.all.mc_forwarding'

Why do I get this message? How can I change this key?

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Because /proc/sys/net/ipv4/conf/all/mc_forwarding is read-only, even for root. It seems like you have to run a multicast router instead of turning this option on directly. – scai Jun 17 '13 at 12:24
up vote 3 down vote accepted

I believe this thread describes your problem

In a nutshell, the proc entry containing that value is read-only, and cannot be made writable easily:

$ ls -ln /proc/sys/net/ipv4/conf/all/mc_forwarding 
-r--r--r-- 1 0 0 0 Jun 17 08:20 /proc/sys/net/ipv4/conf/all/mc_forwarding
$ sudo chmod u+x /proc/sys/net/ipv4/conf/all/mc_forwarding
chmod: changing permissions of `/proc/sys/net/ipv4/conf/all/mc_forwarding': Operation not permitted

But you can run your own router daemon to (e.g xorp) to get multicast forwarding.

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